Shower Waterproof Membrane – Your Ultimate Guide

Comments (133)

• Steve · 11/2/2024

  Hi Onlyhirecertified, The scenario you are describing is not an easy one, but it does sound like your contractor did almost everything wrong. Putting aside the waterproofing issue for a moment, the first problem is that your masonry wall is very moisture permeable, and heat conductive. As such, it’s surface temperature will always be about the same temperature as outside. Whenever there is even a few degrees difference between the inside of your shower, and the exterior temp (the masonry wall surface, in other words), condensation will form on the cooler of these two surfaces. In your case, it will likely be the green board between the masonry wall and the backer board. The only way to avoid condensation would be to adequately separate the masonry wall from your shower wall, and thoroughly insulate the entire space to create a gradual thermal and moisture gradient between the two. This would require the construction of an insulated stud wall adjacent to the masonry wall which will become your new shower wall. Your backer board, waterproofing membrane, and tile would then be installed on this new stud wall rather than the masonry wall. It would also be important to seal the exterior facing side of the masonry wall as much as possible, to limit moisture penetration. As it is, your contractor could apply the “perfect” waterproofing membrane (there’s no such thing, btw), and seal all the seams and corners perfectly, and it still wouldn’t eliminate this condensation problem. A small amount of moisture will always make it through the best waterproofing membrane and condense on the masonry, if it’s slightly colder outside. If it’s slightly hotter outside, moisture from your masonry wall will condense on the back surface of the backerboard. Either way, it’s pretty much a disaster. I’m sorry to tell you this, but I think the whole shower needs to be redone by someone familiar with code compliant exterior shower wall construction in your area. Sorry for the bad news. Steve

• Onlyhirecertified · 11/1/2024

  We live in Arizona. We converted our tub and shower into a his and her shower. The reason for the remodeling was because the floor tile grout cracked allowing water into the shower pan. And to boot the shower pan was cut to make it fit. And the shower pan did not extend up the walls. Shower was installed by previous owner. My concern is that the longest wall in our shower with the bench is an exterior block wall finished with stucco. The bench is constructed of cement block. This wall had a large window that we removed and installed 4 glass blocks and filled in the rest with cement blocks. Because we removed the damaged green board the contractor patched the green board then installed cement board on top. They used some kind of tape on the seems then applied a red colored waterproofing. But, did not apply any waterproofing to the block bench. They did construct a new shower pan but, did not install any waterproofing. The only waterproofing was on the walls. There was not ANY kind of membrane visible from the floor up the walls. Where the cement floor meets the wall there is no gap or tape. We installed a cream and beige marble tile on the entire shower. We were forced to use a mesh floor tile or be charged $700. in addition to labor charges. We used a Chevron pattern so it has lots of grout. Because the contractor abandoned the job it’s still not finished. Based on the information provided did they properly waterproof the shower pan, take measures to prevent grout cracking, and tile discolortion?

• Steve · 7/15/2024

  Hi Phil, I don’t hear from pros that often so thank you for taking the time to read my article and for the compliment. As you probably gleaned from reading my post, I am not crazy about the traditional “water in, water out” shower pan waterproofing techniques. Not that I have anything against them per se. It’s simply because the modern under-tile waterproofing strategy is easier, and frankly better. So to answer your first question… Yes, I think that hop mopping is indeed a dependable waterproofing method for the shower floor as long as it was done correctly and carefully. If so, I think that you can be pretty certain that water will never make it past the membrane and into the framing. However, I cannot say for sure that you will not be getting cracks in your tile assembly, especially at the floor/ wall margin. The problem with this configuration is that it decouples the pan from the wall. As such, the pan moves independent of the wall tile assembly because the latter is connected to the framing; floor tile assembly is not. And as I describe in my post, I don’t think it is a good idea to combine a water-in, water-out system with an additional undertile waterproofing membrane system, either liquid or sheet membrane. As for question 2, I will refer you to my Tile Backer board post for the whole story. I know that it’s likely not what you wanted to hear, but I hope it helps. Good luck with it! Steve

• Phill · 7/11/2024

  Hi Steve, the technical knowledge presented in your articles e.g permeability of different products, make it clear that you are very knowledgeable on the subject of tile backers, and specifically, my most concerning issue, waterproofing/ vapor barriers. I have 39 years in construction experience, mostly commercial but tiling residential showers is certainly not my area of expertise. I have mostly completed rebuilding my residence (while working a full time job), which includes two bathrooms, each with a walk in shower, 4’x 5′ & 4′ x 6′. Now I’m starting interior finishes. I have read your articles and many of the Q&A’s but haven’t found anything touching my situation. Hopefully you can help. I have heard from several sources that the old tried and true method of hot mopping the shower pans is still a dependable method so limited on research time I found a local roofing contractor that specializes in this. This is done. He did a great job sloping to the drain and protecting the auxiliary drain holes around the adjustable drain base. Reading several DIY blogs on showers I haven’t read anyone talk about hot mopping. Question 1, do you feel this is a dependable method of waterproofing a shower floor? If not, what can be done on top of the hot mop surface such as a rubber liner or applied liquid membrane to add longevity to the system? The house has a raised floor, truss joists on 19.2″ centers, 3/4″ T&G plywood, very solid so I’m not anticipating enough movement with foot traffic to cause cracking in the hot mop but now I’m starting to question how long that material will hold up before shrinkage or ? allowing moisture to get to the subfloor. Question 2, regarding the walls. It seems that most tile professionals go to the cement board as a wall backer. One post said he prefers glass mat. A (waterproof?) glass mat made by National Gypsum is available in my area in 4′ x 8′ sheets as well as Denshield in 3′ x 5′. From my experience with any water intrusion situations the devil is always in the details, specifically the joints and material seams are where 99% of the trouble comes from. By using a 4×8 glass mat material it eliminates many of the seams I would have using 3×5 material. And once the seams are taped and a liquid membrane is applied it doesn’t seem to my that the backer material is all that critical as long as one is not practicing their hockey moves in the shower. 2×6 framing. 16″ o c. Very interested in your response. Thank you for the incredibly knowledgeable articles.

• Steve · 1/18/2024

  Hi Matt, Thanks for the comment and the recognition. Really appreciate it. Steve

• Matt Evans · 1/12/2024

  Thanks for the in-depth look at this. I am a contractor and always like to see more perspective and ideas.

• Steve · 12/20/2023

  Hi Steve, Thank you for your comment! The “concrete slab” on your second floor is most likely a cementitious material that is much lighter and much weaker than concrete. As such, it would be easiest if you just left it alone and installed your pan over top of this (above grade). This material is not very stable and will crack easily if you mess with it. If you choose this route, I would suggest that you install a prefab foam shower pan. The Wedi pans are great. They have both a recessed pan and a standard pan with curb. They come in many different sizes and can be modified. I really like these pans because they have a cementitious coating with imbedded fiberglass mesh, so the surface is very rigid & impact resistant compared to other foam pans. If you decide on a “curbless” shower with a custom mud pan, you’ll have to cut away your “slab” to install it. When installing the Wedi Fundo Ligno, you might also need to remove the “cement” subfloor, but it will depend on the depth of the surrounding floor materials you choose. A custom mud pan could work out quite well because you have a full 4 inches depth to work with. This depth will allow you to create a super solid mud pan (make sure framing beneath is fortified to take the extra weight). If you’re interested, here’s a great video by Schluter Systems. You’ll notice that a membrane bonding drain assembly is used in both of the above installs, and I would suggest that you use one as well. You can’t really go wrong if you use the materials suggested, and follow the directions. Good Luck! Steve

• Steve W · 12/19/2023

  Excellent information, thank you The RedGard is a way better option than the thick cumbersome rubber membrane the associate at my local warehouse store insisted I would need to install. Even more odd considering that they also sell the RedGard. I’m replacing a tub with a shower in a 2nd floor bathroom that has a 4″ concrete slab. Any advice for what type of drain to install to minimize the depth of concrete removal from the slab to install the drain or any other helpful advice for this project?

• Steve · 11/29/2023

  Hi Kim, Thank you for your comment! I like this board and have used it a fair number of times, but one annoying thing is that it’s around 1/16″ thinner than most other tile backers. Not a deal breaker but your contractor might complain. The reason you are applying thinset in the corners is only for installing the fiber mesh tape. This is extremely important in order to reinforce the joints. This is what James Hardie says: “Fill all joints with mortar (see “Materials Required”). While mortar is still workable, embed minimum 2 in. wide high-strength alkali-resistant glass fiber tape in the mortar and level.” The only extra step I would recommend is to cover the entire board surface with the liquid membrane. Even though they call this board “waterproof” it doesn’t really have a great moisture permeance rating (in my opinion), so enhancing it with a liquid membrane is a good idea. It’s also pretty easy to do since you’ll be applying the liquid membrane in the corners anyways. You can use any of the big name liquid membranes, RedGard, Mapei Mapelastic HPG, Laticrete Hydro Barrier, or others. You can also skip all of the liquid membrane stuff, and install a good sheet waterproofing membrane instead. This is always my preferred waterproofing method since I personally demand the highest perm rating possible, especially if your shower is on an outside wall. Good Luck! Steve

• Kim · 11/29/2023

  Hi Steve I am doing a shower remodel and plan on using Hardie backer board with HydroDefense. They say to just cover the joints with thinset and cover with a liquid waterproof membrane. Thoughts? Do you have a recommendation for the liquid membrane? They also say to use the same thinset as you will be using for the tiles.

• Steve · 10/7/2023

  Hi Angela, Thank you for your comment! Unfortunately, I can’t really provide much advice on this because I’m unfamiliar with any adhesive tile installation system that are designed for showers. I should say that none of the waterproofing membrane systems that I’ve mentioned in my article would be compatible with adhesive tiles. That much, I am quite certain about. Only thinset mortar and standard ceramic or porcelain tile should be installed on these membranes. Personally, I would not consider installing adhesive tiles in a shower, regardless of the system being used. Too big of a risk. Sorry for the bad news. Steve

• Angela · 10/5/2023

  I don’t think it can be said enough- thank you for this content! Do you have any particular membrane recommendations for a tile system that is affixed with adhesive rather than mortar? Thank you again Angela

• Steve · 9/4/2023

  Hi Ron, Thanks you for your comment! The drain assembly is most often the cause of shower pan leaks. You mentioned “we fixed that” but the drain might require some further investigation. Another problem I’ve seen a few times before is a hairline crack in the acrylic. These can be very difficult to see unless someone is standing on the base. To test both of these hypotheses, you should do a “flood test”. Plug the drain and fill the base with water up to the top of the curb. Then just wait a few hours to see what happens. Someone should also step into the shower during the test, to see if any cracks might open up when pressure’s applied. If there are no leaks during the test, then you can at least rule out the pan and drain as the cause. Good Luck! Steve

• Ron · 9/1/2023

  Great article! We installed a shower base 3 years ago and tiled the walls. We noticed a lot of moisture on the floors for a few years but assumed it was the water seeping out when the kids got in and out of shower. The bathroom is on the second floor & a few weeks ago water was dripping from the ceiling. We cut the ceiling to see what’s happening and figured it was the drain. We fixed that but the same problem occurred. We did a few tests and sprayed water on the tile in the shower & noticed the water is somehow getting between the acrylic base and subfloor. Upon installation we put Kerdi board on the wall (behind tiles) and house flashing tape over the flange. We can’t figure out what’s happening. The supply lines are not leaking. We ruled out the drain. We can’t understand how water is getting between the acrylic base and subfloor?..

• Steve · 8/27/2023

  Hi Barry, Thank you for your comment! Since you’ve read my post, you already know why I don’t like the traditional mortar base with shower pan liner beneath (water in / water out system). So if you are suggesting that floor heating system underneath may help alleviate the problems associated with this system, I would suggest that you’re barking up the wrong tree. It’s likely to cause more problems than it solves, in my humble opinion. I’m assuming that you’re thinking about a copper pan liner rather than rubber, for obvious reasons. But floor heating under a copper pan liner could also be problematic for many reasons. I can only image the horrors that could result from heating a moisture saturated mortar base from beneath. Some of these horrors… Rapid expansion of water into vapor, which will cause cracking and movement of the mortar base, and the entire tile assembly. Drying of the base from beneath could also likely cause dissolved calcite to re-crystalize, blocking the water from flowing to the drain weep holes. This along with a warm, & cozy place for toxic mold to thrive. Honestly, this is the stuff of nightmares for me. My recommendation… install some mesh on the subfloor, lay your mortar base, clad the walls, and waterproof over top. A simple, proven, bulletproof shower waterproofing strategy. Good luck with your project! Steve

• barry thompson · 8/26/2023

  I just discovered your website and I’m impressed. It looks like you went through a period of time thinking about successful shower-builds while you fell/fall asleep at night- THANK YOU for doing that!!!! I understand your thoughts and suggestions on selecting the the best shower build components and utilizing the best building practices- MUCH appreciated. While NOT trying to change your mind, I would like to offer up a potential option that ‘may’ lesson the risk of an eminent failure from a traditional cement and membrane shower base, due to the accumulation of moisture. Perhaps you have thought of this and ruled it out- if so, I would be very interested in your thought/rational process. For those of us who seem hell-bend on a traditional concrete/membrane shower base, if ‘floor heat’ was introduced under the mud bed, would THAT lessen your concern for an eventual pan failure? From ALL of us, THANK you in advance for a response!

• Steve · 8/21/2023

  Hi Dan, With an exterior wall of masonry construction, it’s even more important to have at least 3 1/2″ of space between the backer board and the outside wall surface. Regardless of the thickness of the masonry, the inside surface of this wall will be essentially the same temperature as the exterior, which makes it a perfect condensation surface (masonry is very efficient heat conductor). An additional confounding issue can result if the exterior masonry surface is directly exposed to the rain (if the wall doesn’t have any exterior cladding or rain-screen). If this is the case, the wall can be permeated with a relatively high degree of moisture all year round. This adds to the moisture concentration within the interior wall space, making your shower waterproofing efforts nearly futile. My recommendation would be to make sure you have some sort of cladding or rain-screen that keeps rain off the exterior of your masonry wall. Without getting into great detail (I could write an entire essay about this)…You really need to do this, not only for your shower remodel project, but for the “health” of your entire home and its occupants. Second recommendation would be to build at least a 3 1/2″ stud wall between the shower and the outside wall, and fill it completely with insulation (no gaps), preferably spray foam (for its higher R-value & lower moisture permeability). Then board it and waterproof the shower in the usual way. I would suggest that you talk to a waterproofing expert in your area. They will know the best way to do this, based on your local climate and building code. Good Luck with your project! Steve

• Dan · 8/16/2023

  I am wondering about what vapor barrier to use when the external shower wall is concrete block and only allows 1/2 inch of rigid foam and 1/2 off backer.

• Steve · 7/7/2023

  Hi Rebecca, Thank you for your comment! A curbless shower is a tricky thing when it comes to the building code, because it varies so much between jurisdictions, and has often not been updated to accommodate this type of installation. You should always enquire with your local building authority to ask for written AND verbal instructions about the local code regarding building curbless showers (and the flood test). If there is no specific written requirements for CS’s, the code will likely be interpreted by the inspector at his/her discretion. In my experience, the safest approach is to treat your entire bathroom as the shower pan. In other words, installing a “wet room”. There are a lot of articles online about this, so make sure to do your research before you begin. On some of my CS projects, there was no flood testing because the inspector didn’t really know how to deal with it, but I’ve also been required to flood the entire bathroom on other jobs. As I said, this will totally depend on the local code and the inspector. Whenever I build a curbless shower, I pretty much always waterproof the entire bathroom floor (sheet membrane, always) and bring it up the the wall a few inches. Even if I’m installing a floor heating system (like Ditra Heat), I always overlap the shower base waterproofing over the Ditra Heat mat, and seal all the seams. If you guys are attempting the shower base installation yourselves, I would strongly recommend installing a pre-formed foam shower pan like Wedi Fundo Ligno. It’s much easier because you don’t need to waterproof the pan itself, only the margin between the pan and floor membrane. Good luck with your project! Steve

• Rebecca · 7/7/2023

  My husband and I are building a house, and we’re trying to get ready for our pre-drywall inspection. We were told that we have to have the shower waterproofed to do a flood test before the inspection. We are doing a curbless shower. It is about 8 ft. long and 3 ft. deep. We will have a glass panel covering about 5 ft. of the opening, but no door. We will probably do a dry mortar bed to make the slope, and then some kind of membrane for the waterproofing. My question is, how do we get it ready for the flood test? Since it’s curbless, it will be level with the bathroom floor, so what do we need to do to prepare it? Also, how would we install the waterproofing membrane without a curb? Every video we have found has a curb for the shower. We would really appreciate your advice! Thank you!

• Steve · 6/15/2023

  Hi Kaitlyn, During a “repair” motivated shower remodel, there’s always a desire to keep a perfectly good shower pan that seems to be in good shape, rather than ripping it out and starting over. I get where you’re coming from, and I’ve been there… many times. However, as you’ve probably gleaned from my posts, I am not a fan of classic shower pan engineering, especially when it’s combined with the newer shower waterproofing techniques. In short, I would say that combining these two systems is a bad idea. In your situation, there’s a little more latitude, because there are no outside walls, but you will still likely have problems at the margin between the wall membrane and rubber liner because there’s too much movement in shower pan and tile assemblies with rubber liners beneath. And there’s no safe way to make the transition between the rubber liner, and the newer style decoupling/ waterproofing membranes, regardless of whether a sheet or liquid membrane is used. It makes me shudder just thinking about it, if I’m honest. I know you don’t want to hear this, but I would tear out the shower base and install a new mortar base directly over the substrate (with a membrane bonding drain assembly), OR install a prefab foam shower pan. That way, you can install a completely compatible and unified sheet or liquid waterproofing/decoupling membrane on the pan AND walls with no worries about the margin between the two. Good luck with your project! Steve

• Kaitlyn · 6/15/2023

  I am one of those whose shower niches leaked … probably for a very long time. The unused storage closet that backed to the shower was totally molded. I demoed everything and elected to use shower baskets. I am remodeling a different shower and want a larger niche if possible. I do not plan to remove the existing mortar and rubber pan, which extends almost 18” up the wall. Is there a reason not to do the following Run a piece of the rubber pan material from about 10-12” above the bottom of the niche, around the edges and down to the inside of the existing pan. Then frame out the pan, apply cement board, an unlocking membrane and then tile. Since the perm on everything except stainless is greater than 0 and since I already enjoyed the prior mess, would this cause a problem? It is an interior wall in the south (rarely freezes). I think it would guide any moisture down to the pan and not to the studs. I’m probably missing something though.

• Steve · 5/9/2023

  Hi Lori, Thanks for the comment! If I’m understanding you correctly, you are concerned about the margin between the tub skirt and the tile floor mainly because water from the adjacent shower may/will be splashing on this margin. If that is the case, I would have first waterproofed the entire floor in this room (creating a “wet room”), before installing the tub. I’m also assuming the shower is “curbless” and there’s some floor space between the edge of the “shower pan” and the tub. In this situation, the tub would be installed on the membrane after the shower pan was installed and the wet room was created. The floor tile would then be installed outside the tub and against the tub skirt in the standard way. A simple silicon bead would then be applied at this margin, in the same way it would have been applied had the tub not been installed in a shower room. In other words, it is the waterproofing membrane beneath the tiled floor (and tub) that ensures the waterproofing integrity of this margin (and the room). The silicon bead simply prevents liquid water from penetrating the gap. I hope that helps. Good luck with your project! Steve

• Lori · 5/8/2023

  Installing a,shower room with alcove acrylic tub and tile shower inside shower door. everyone is stumped how to waterproof/seal shower floor against the tub! help!? It is a,skirted tub not drop in acrylic.

• Steve · 4/23/2023

  Hi Pete, Thank you so much for the comment and the compliment! 1. I ONLY way I would extend a foam shower base is by using dry pack mortar. Here is an awesome Schluter video showing how to do it. Another thing to consider is simply ordering a custom foam shower pan that fits your space. I have installed a Noble custom shower pan several times for custom showers. Noble Company is a super solid company, but there are others out there doing the same thing. 2. I’m not sure exactly what you are asking here, but I would say that combining different membranes is generally not a good practice. I would also say that the margin between the shower base and the wall should ALWAYS be sealed with a sheet membrane (ex: Kerdi Band & Kerdi Kereck), not a liquid membrane. There is always some movement in this joint, and it’s way too important to rely on a liquid membrane. Personally, I rarely install liquid membranes. The results are too variable. Use a good sheet membrane. A little more hassle is worth the peace of mind. 3. I would suggest that you just follow the linear drain install instructions carefully. It would really help if you used a linear drain brand that matches the shower pan you buy, then the instructions will be complete & detailed enough for any DIY’r. 4. Yes!! I would wholeheartedly recommend that you do this yourself! Installing shower pans is definitely intimidating for most DIY’rs, but it’s actually quite easy if you take it step by step. AND… it comes with a great sense of accomplishment when your done. Good luck with your project! I’m rooting for you! Steve

• Pete · 4/23/2023

  Steve, this is an amazing blog! I learned more by reading it in 30 minutes than in countless hours of watching youtube videos! My problem is more labor related than anything: I’m building a vacation house in a remote area, where skilled trades are tough to come by. The tile/flooring contractor that entire area was using discovered wonders of dating services and decided to move to the other coast (how could he dare :))! I talked to a couple of more local guys but their knowledge of tiling and waterproofing seemed to be at my level. I convinced a friend of mine, who is a general contractor, to take a break from his busy schedule and drive 6 hours to install the tiles in my 2 bathrooms. But he neither has time nor is willing to waterproof them. So, I’m thinking of doing the prep and waterproofing work on my on. The problem is, the master bathroom’s walk-in shower is oversized (7’x4’) with a linear drain (all rough-in plumbing for it is completed too). I would love to use the foam shower base and cover it with a membrane, but the biggest ones I found are 76”x38”. So my questions are: 1. for the remaining 10” at the perimeters, am I OK just to use a flat foam (no slope) to cover the gaps to the side walls and the curb? 2. As the shower is oversized, is it OK to combine the membrane (base and around it, along the shower fixtures wall, corners) and use the redgard for the rest? 4. Do you have any advice re the linear drain connection to the p-trap and the foam base? 3. I’m very handy but for this work I wonder If I’m too crazy to take on it?

• Steve · 3/4/2023

  Hi Linda, Thank you for your comment! If the walls surrounding your alcove bathtub are not exterior walls, you shouldn’t have to worry about any vapor retarding plastic sheet behind the backer board. If by chance, you know that there is one there, you need to remove it. Simple as that. It will only cause problems if you leave this sheet in place, RedGard or not. If there’s no plastic sheet behind the existing Backer Board, and the BB surface is in good shape, you shouldn’t really need to replace it, but… I would be concerned if there was a lot of adhesive stuck to it’s surface (from the original vinyl panel installation). If you can’t clean off most of this glue, I would replace the backer board. You can’t assume that RedGard will stick to it. You should always apply your waterproofing membrane on the entire shower surround, from tub to ceiling. No exceptions. There should be a flange around the perimeter of the tub (about 3/4″ above the tub rim) that allows it to be attached to the studs. The backer board should terminate just above this flange. The margin between the flange and the BB should be sealed somehow (silicon or some other sealant). This limits water vapor from penetrating this gap. Only the wall tile should extend past the edge of the BB, down to the tub surface (with a bead of silicon to seal it). If the backer board extends down to the tub surface (tub rim), that means it’s installed incorrectly, OR the tub has no flange around it’s perimeter. If the tub has no flange, the tub should be replaced. Good Luck with your project! Steve.

• Linda · 3/4/2023

  Hello! My house was built 22 years ago. We have a cast iron bathtub with a vinyl tub surround. The builder never got around to tiling before he left . I am finally planning to remove the vinyl surround and install subway tiles. We are also adding a rain shower head and a glass shower door. We have never showered in this bathroom and the cement board is in perfect shape. Can I just apply Redguard the current backer board? Or do I need to install a newer type wallboard? I don’t know what kind of vapor barrier is behind the wall. Would I find it just underneath the backer board or underneath the insulation? I know you should not have 2 vapor barriers but I definitely want to apply Redguard. If I only tile up the wall to above the shower head, will the wall above the tile allow for moisture to escape and prevent mold? The tub is on inside walls. Also, how do I address where the backer board meets the silicone caulk line at the bathtub edge? Thanks so much !

• Steve · 2/13/2023

  Hi Sheldon, No worries about the long message. Unfortunately, the situation you are describing is a bit more complicated that it may seem. It’s great that your shower doesn’t have any obvious “leaks”, but it doesn’t mean that you don’t have moisture problems within the wall cavity and in the roof line. In a 1960’s home, I can guarantee that moisture (water vapor) has permeated the walls surrounding your shower (and the rafters above it) ever since the shower was installed. And I can also guarantee that this moisture is condensing (into liquid water) in these spaces, especially during the cooler months of the year. This doesn’t necessarily mean that there is a lot of nasty black mold growing in your walls, but there is definitely some degree of problem there. In other words, I can’t really recommend this kind of surface treatment because it doesn’t really address the problem I described. A sealer might help prevent future “leaks” but you already seem to have that problem well in hand, with your periodic caulking efforts. So… unless you are interested in taking on a full shower remodel, I would suggest that you just leave it the way it is for now. Let the next generation deal with it! Steve

• Sheldon · 2/12/2023

  Hi Steve, What an amazing report and gift to installers and their customers! I came across your work when googling to see what I might put/paint on the inside of an old shower to add years before it needs to be totally ripped out and rebuilt. At 80 years old I’m glad to have it last however many more years I may have and leave a lovely rebuild to the next generation. The shower is on the second floor of a retreat home and was installed in former attic space — along with the rest of the bathroom and two bedrooms — by my parents around 1960. So 60 years ago. The shower has an exposed cement floor that is solid and doesn’t leak. The walls are the old fashioned tile hardboard that came in sheets — shiny on one side (the waterproofing) and imprinted with 3″ or so squares with deeper imprinted fake grout lines between. The corners where panels meet has a metal 90 degree molding for the panels to slip into. In recent years I’ve used silicone in a caulking gun to give extra waterproofing to the joints. Same silicone along the floor where panel meets cement base. The bathroom is really weird — due to slope roof and other constraints — and the shower is quite small and the door is positioned so you have to go round a corner to step into the shower. Being tucked away we don’t much care what it looks like, as long as it is functional, can be cleaned and is waterproof. So far the shower hasn’t leaked but we’d feel better IF we could do something like paint a clear coating of something over top of the existing hardboard that would last 10 years — at 80 likely a lifetime guarantee! — that would be great. Do you know of such a product? Sorry for such a long message but figured the more you knew the more likely you could help. Thanks! Sheldon

• Steve · 3/29/2022

  Hi Paul, Thank you for your comment! I’m happy to hear that your taking on such an involved project! First of all, NEVER use standard gypsum wallboard on the curb or walls of your shower. Even with a good membrane, this board will absorb/ retain moisture, and has very poor compressive strength. Use only shower tile backer board. I would suggest that you install a prefab foam board niche or custom modify your own custom sized foam niche. No need to worry about sheet membrane corner waterproofing of your shower niches! I would also suggest that you install a cement coated prefab foam shower pan but if you really want to install your own mortar pan, here’s another good video. I would not recommend overlapping liquid/sheet membranes but if you need to for some reason, always install sheet membrane over liquid. Almost all the sheet waterproofing brands sell “valve and pipe seals” (Durock, Mapei, Wedi etc.), but they’re a bit harder to find. You might have to visit a tile supplier/ wholesaler for some of the less common brands. Good luck with your project! Steve.

• paul · 3/27/2022

  What a great article! Awesome, useful information! Planning our fairly simple, not very large shower stall and have been obsessively watching hours and hours of YouTube videos! Looking at the options, I am wondering which materials are most compatible. I am framing in a pretty large and deep double niche (framed with 2 x 6 thanks to a deep wall which the previous installer made to accommodate a smaller shower pan) From videos I’ve seen, the corners and edges can really build up with all the overlapping membrane material. Wondering what you think about the following combination of materials, and I’m not totally clear on the exact order of operations: 1. Build curb, cover curb and walls with a wallboard (cheap 1/2″ drywall ok, or do I need to use another backer for the membrane? 1a. Going to tilt the wallboard of those lower niche sills with thinset underneath 2. Hand slope a mortar pan (I want to use the Flo fx drain flange) (ok for the mortar bed to contact the wall backer (which goes down to the slab) right?) 3. Wedi or hydroban membrane on the floor first, then all the walls 4. Wondering if I could use a liquid membrane for the niche only, in order to avoid trying to wrap all of those corners?? If so, how does one interface the sheet and liquid membranes? Paint the liquid a few inches over the sheet where they meet? And finally, does anyone besides kerdi make those rubber flange pieces that fit around the valve control? How do you address this when using the other membrane systems? Thanks again for all of the info and any guidance!

• Steve · 3/14/2022

  Hi Marika, Thank you for your comment! This is an interesting and surprisingly complex waterproofing question. Corian’s claim that it’s “100% WATERPROOF” isn’t really that helpful. This would be a very basic expectation of any solid surface wall material. Moisture transmission is what you need to be concerned about when considering shower wall surface materials. Moisture will ALWAYS move through the shower wall and enter the wall cavity no matter what material you use, it’s just a matter of how much will get through. That’s why “moisture permeance” ratings are so important and why all waterproofing membranes have a perm rating – it’s the only way that you can compare their effectiveness. Corian “can be installed over most existing surfaces” using regular silicon as an adhesive, according to their instructions. They mention nothing about any additional waterproofing requirement beneath this product. As such they should really be publishing a perm rating for this product, and I can’t find any mention of it anywhere. In other words, it’s impossible to say how good Corian is at limiting moisture transmission, but I would not recommend applying a waterproofing membrane behind it regardless. Sheet waterproofing membranes are designed for tile and mortar application, not silicon. Silicon might stick well to a liquid membrane, but I wouldn’t recommend this either because the air gaps between the Corian & the membrane would trap moisture. I would recommend taking all the additional precautions I mention in my post (increase stud wall depth, lots of insulation), to minimize the risk of condensation in the outside wall cavity. And if the material comes in different thicknesses, I would try to get something thicker if possible (thicker than 12mm), since this will be your only waterproofing layer. Yes, Kerdi or Wedi board would be a great idea for the ceiling. Good luck with your project! Steve.

• Marika · 3/14/2022

  Wonderful article, so very informative! We will embark on a master bath reno soon, and hoping you can answer some questions before we start. Waterproofing is our main concern and would like to get it right! We will remove the existing tub/shower combo from the 80’s, and plan to replace it with a walk in shower. The back wall is an exterior wall, and the side wall is not. 1) What would you recommend for water proofing, so that we can use the same product on both walls. We decided not to install tile, and have chosen corian walls instead – seamless, no grout lines and waterproof. 2) Current ceiling over the old tub/shower combo is the standard dropped ceiling common in the 80’s. We’d like to remove the drop and raise it, so the bathroom ceiling is all the same height. Would you recommend a Kerdi/Wedi/etc board for the ceiling above the new shower? The plan is to paint the entire ceiling a white color. 3) Will be installing a corian shower base as well, and wondering about any waterproofing requirements below it on the subfloor. We’re skilled DIYers, but this is our first bathroom reno.

• Steve · 3/11/2022

  Hi Louis-pascal, Thank you for your comment. I would recommend against using anything other than sheet or liquid waterproofing membranes designed for shower waterproofing. The biggest problem with blueskin is that its surface is not designed to be tiled upon. I suppose you could apply a sheet waterproofing membrane over it, but this would just amount to a bunch of extra work for no additional benefit. Stick with the materials that have been engineered and tested for shower wall waterproofing. That would be my advice. Good luck with your shower remodel project! Steve.

• Louis-pascal · 3/11/2022

  Thanks for all the info . I was wondering if I can use blueskin membranes for my shower tiling project ?

• Steve · 2/14/2022

  Hi Angie, The best way to answer your questions is to refer you to a great video from Schluter Systems. This video shows exactly how to properly waterproof an entire shower with a mud shower pan, using their Kerdi waterproofing system. The “under tile” waterproofing with the integrated membrane bonding drain assembly is the key to this system. It eliminates the flawed pan liner and drain system that many “old school” installers still use today. To avoid the many problems associated with this backwards pan assembly, I would MAKE CERTAIN that your installer uses the install method in this video. He/she does not necessarily need to use the Schluter system, but a sheet membrane system with an integrating drain assembly is essential in my opinion. Don’t be afraid to ask your installer to watch it as well. This is a procedure that requires a careful attention to detail so it’s worth damaging his/her pride a little bit. It sounds like a fun project. I wish you the best of luck with it! Steve

• Angie · 2/14/2022

  We have torn out our shower and tub in the master bath down to the foundation. We are building two 4′ enclosure walls that are 7′ for 2′ the descends to 4′ over the next 2′. The walls will have a slight curve inwards at the end and attach to interior side wall both witb plumbing in them. Turning it into a his/her shower. We are using 2×6 studs because we were told that the wall had to be 6′ wide to install nitches. The reason why we are doing this remodel is because the shower was leaking into the exterior block walls. Whomever installed the shower pan cut it to fit. In doing so the pan didn’t go under the wall panels. “Waterptoofing” is important to us. We are using a mud man to install the tile. As our shower pan will be custom what waterproofing precautions should we take? Should the waterproofing on the floor go under the new enclosure walls as well as the threshold ledge. Maybe a dumb question but, does the waterproofing membrane go on top of the green board on both sides?

• Steve · 9/11/2021

  Hi John, Thanks so much for your kind words. I’m glad you got something out of it. Good luck on your project! Steve

• John Chipman · 9/10/2021

  I am doing a bathroom remodel right now. Your article was incredibly well written and thorough. Thank you!

• Steve · 8/31/2021

  Hi Daniel, Good questions! It’s always the best idea to stay with one shower system and not mix products. It doesn’t mean that this can’t be done safely (I have been forced to do this on a few occasions) but it does have warrantee implications. You will have to make the judgement yourself whether it’s worth the risk, but it would likely be impossible to start any warrantee claim if products are mixed in this way. But I should also say that even if you install all the same shower system components, a successful warrantee claim of this kind is very difficult if things go sideways. There are a lot of burdensome conditions on most of these warrantees. It’s not a terrible idea to use Kerdiboard (I would use Wediboard instead) but if he plans to waterproof the corners with a liquid membrane instead of Kerdiband, I would fiber tape the corners first. In my opinion, liquid membrane without fiberglass reinforcing tape is a bad idea no matter which board you choose. A prefab foam bench is the best idea for the shower. No matter how good your membrane is or which board you choose, a wood framed bench will absorb a tiny bit of water vapour and expand / contract with changes in temperature. Water may never get past the membrane and into the framing, but you would eventually end up with grout line cracking and possible tile delamination. Good luck with your project! Steve

• Daniel · 8/30/2021

  Hey Steve, My parents recently moved in with us (in-law suite) and my father has hired someone to renovate their bathroom. The main issue is my father has poor mobility and the shower is a tub/shower combo. The guy doing the work spec’d cement board. I began doing some research and discovered your blog along with various YouTube tutorials. Anyways I spoke with the guy doing the work if he had installed a Schluter system and he said yes. However, he claimed that he could do it with Kerdi Board and liquid membrane sealer (marpei iirc). My question is, is it okay to mix and match these various membrane waterproofing systems? Could one use a liquid membrane over seams instead of tape? Could one use kerdi board on the floor and a different brand membrane for the floor? Or are these products (and warranties) built so if you buy into one part you are stuck with everything? Last question. Is there a reason to buy a prefabbed foam bench, or could one build it out of wood, cover in a membrane board and sealed as a shower seat? Sorry I’m a novice here and appreciate the info.

• Steve · 8/4/2021

  Hi Brennan, Thank you for your comment. I always install a single layer of backer board about 1/8″ away from the top of the tub mounting flange. The tub mounting flange is slightly less than 1/2″ in thickness which makes the 1/2″ backer board surface slightly proud of the flange. It was engineered this way so that your waterproofing membrane and tiles can overlap this flange, creating a drip edge. The only additional thing I would suggest is to fill the 1/8″ gap between the board and tub flange with polyurethane sealant. Since you are installing glass matt board, I would pre-seal the bottom of the exposed gypsum end with a bonding agent like Weldbond (diluted) so the sealant adheres to it. A simple rule to use is to remove the vapor barrier plastic from the stud face in all areas where your undertile waterproofing membrane will be applied. This should be done regardless of the membrane you decide to use, but I always recommend using a really good sheet membrane on any outside wall (like Subliner Dry, Kerdi DS) to reduce moisture permeance as much as possible, especially if it’s a 2×4 stud wall. If you overlap the waterproofing membrane (on the backer board surface) over the plastic vapor barrier sheet (on the stud surface), moisture will likely be trapped between these layers and condense into water on the surface of the plastic sheet. You don’t want that. Good luck with your project! Steve

• Brennan · 8/4/2021

  Hello, my name is Brennan and I am currently undertaking a bathroom renovation in the Okanagan. 1) I had a look in the TCNA, and it says to over lap the tub lip with the tile backer board minus 1/4″ from the tub surround, from your experience is this correct? Further, is it problematic to double up the tile backer board to achieve this over lap off of the stud wall? I am using a USG glass matt tile backer, I called the manufacturer and they said, ” it should be fine”. What do you usually use to space it past the tub lip, plywood? In one of your posts you mentioned to remove the plastic vapour barrier if you have an exterior wall in your tub surround, I have an exterior wall in my tub surround, the layers are as follows… vapour barrier, aqua board (green board), USG glass matt tile backer board. 2) Do I need to remove the vapour barrier behind these layers of wall board, seal the vapour barrier on the exterior studs around this wall panel, then install 1 layer of tile backer? Do you recommend a vapour barrier behind the glass matt tile backer board on the other walls or is it the same concept, just one vapour barrier (glass matt tile backer)? I noticed a guy on youtube putting vapour barrier half way up, thoughts? Kind regards, Brennan

• Steve · 6/29/2021

  Hi Marcus, Thank you for your comment! I’m not sure what the people at Schluter would say about your idea but I would say that its not a good idea. Because the Ditra matt was designed as a “decoupling membrane” as well as a waterproofing membrane, it wouldn’t be an appropriate substrate for a shower base. A shower base should always be structurally connected to a non-deflecting subfloor. The “decoupling” part of this membrane violates that rule. The standard Ditra install is fine in your situation with 1/8″ to 1/4″ gap between the Ditra and pan and Kerdi-fix is a fine idea too. Good luck with your project! Steve

• Marcus · 6/28/2021

  Such a fantastic post thank you so much for your efforts. When i first came here to have a read i was already dead set on kirdy Ditra floor membrane and either the foam backer boards or the kirdy 200 wall membrane (not decided yet) for the walls. But! My question is.. I want to fit a resin cast shower tray (Mira flight). I’m thinking to cover the ENTIRE floor and walls with Kurdy including sealing – all joints, corners and wall to floor transitions. And then set a mortar bed and set the resin tray – ON TOP of the kirdy ditra? Or should i set the mortar bed and tray straight on to a primed subfloor first. Then kurdy ditra up to it, leave a quarter inch expansion gap and fill that with kirdy fix? I think the first option would be best so the tray is fully waterproofed underneath, but.. will that cause the mortar rott problem you mentioned with mixing two systems (although i think you were just talking about putting a membrane on top of a tray, and i’m talking about continuing the ditra under it) What do you think?

• Steve · 6/5/2021

  Hi Tana, That sounds like a very interesting shower install project however it may be problematic managing moisture in such an enclosed and poorly insulated space as a bus. Generally speaking, a shower wall made from corrugated metal will have an extremely low vapour permeance rating, so you don’t really need a “waterproofing membrane” as such (this is assuming that the panels will be installed with gasketted screws and have no significant penetrations). Your biggest problem will be water vapour management in the room in general. One thing is quite certain… You’ll need a very good ventilation system! Even with great ventilation, it will be extremely difficult to prevent moisture from condensing on all the uninsulated metal and glass surfaces in your bus. To start with, you definitely need to fill the gaps behind the shower panels with spray foam because moisture will surely be condensing in this space. Your main goal will be to isolate, insulate, and ventilate the shower area as much as possible to keep the moisture from reaching and condensing on the many metal and glass surfaces in the bus. I don’t envy you because this is going to be difficult! But I wish you the best of luck! Steve

• Tana · 6/4/2021

  Hi there! I am installing a shower in a converted school bus. I had originally planned on using tile but have decided to use corrugated metal as the siding for the bathroom due to weight, cost, logistical, and aesthetic considerations. Currently the bathroom is only framed with water seal painted plywood. Could I use the methods explained above on the plywood walls under the metal and then seal the metal edges with silicone or do the methods above require a grout layer to be applied directly on top to seal them in? Any suggestions on a method to use as there will obviously be an air gap between the metal and the walls/curved ceiling?

• Steve · 4/30/2021

  Hi John, Thank you for your comment! I think your concern is justified. You might as well make your best attempt at doing it correctly and carefully, now that you have a chance. A regular vapour retarder sheet plastic is still a good idea under the tub. There is little chance for condensation in this area since there is no trapped air. So yes, you should cut away the vapor retarder plastic where the Durock is being installed. I would prefer that you use a good sheet waterproofing membrane instead of Redgard, especially if your outside wall is only 2×4. By removing the vapor retarder you are allowing some water vapor to enter the stud cavity so you need to limit this as much as possible with a good membrane. In my opinion, even with adequate insulation there’s not enough distance from the shower wall to the outside wall to allow the vapor to dissipate & prevent condensation (when using a liquid membrane). I would be OK with the RedGard if you fully insulated the wall with polyurethane spray foam, but not otherwise (if it’s 2×4). You can overlap the Durock over the edges of the vapor retarder plastic to create the seal as long as it’s outside of the shower area and the membrane extends to this point. In other words, the Durock-drywall margin can be slightly outside the shower zone because it can taped, mudded & finished just like regular drywall (even over the sheet membrane). With any liquid membrane I always recommend taping the corners. The Durock should be mounted on the stud surface, about 1/8′ above where the tub flange is attached. Because the Durock is slightly thicker than the mounting flange, your wall tile can be extended below the bottom of the board to the tub surface. The Durock/ tub flange gap should be sealed with polyurethane sealant to prevent moisture from entering. Silicon wont stick to the Durock. The tile/ tub margin is then sealed with regular silicon after grouting. Good Luck! Steve.

• John West · 4/29/2021

  Hi doing a alcove tub rebuild, to replace a leaking whirlpool tub. One side of the alcove IS AN OUTSIDE WALL. Originally there was the vapour barrier over the studs and insulation, with cement board on top with tile applied to it. Im replacing the cement board with Durock and then apply 2 coats of Redgard. In reading your article (great by the way) Should I cut out the plastic barrier just in the area here the durock will be installed? Do I need to try and attach the plastic to the back side of the durock edges? Silicone calk? Normally with a vapor barrier you want to keep the integrity. So cutting it makes my head hurt. There would still be the plastic below the tub, again trying to figure out how to keep some integrity to the barrier. Perhaps I’m overthinking it. Is there a tape that should be used in the corders with the redgard? I know you like the sheet barriers, redgard just seems faster and easier. On another note On this outside wall I was just going to butt the durock to the tub flange. To keep the durock even with the adjoining drywall. What do you use to join/cover the seam between the drywall and durock? Compound? Thinset? On the back and inside I was going to build out the wall 1/4″ so the durock could go over the flange. Thoughts? Do you like the durock to sit on or over the flange? Does it matter? I’ve seen both done on the web. Thanks for your help.

• Steve · 4/25/2021

  Hi Kenneth, Thank you for your comment! Yes, I would say it’s not necessary (or appropriate) to apply RedGard around the Hydro-Blok drain. Good luck with your project! Steve.

• KENNETH ADESSA · 4/23/2021

  Hydro Block seems perfect. Would it be overkill to use Redguard around the drain?

• Steve · 4/3/2021

  Hi Travin, Thanks for your comment! If it’s a shower that you’re building, I would recommend that you waterproof it identical to a regular home shower. That would mean starting out with a good tile backer board. Plywood is Ok if you install a really good waterproofing membrane, but a real tile backer board is better because it’s slightly more rigid and will not retain water vapor like plywood. As well, I would install a good sheet waterproofing membrane instead of a liquid membrane. It’s not a huge issue but as I say in my post, sheet membranes are more reliable and less prone to install error in my opinion. Good luck with campervan shower! Sounds like a fun project and a great upgrade! Steve

• travin Silvers · 4/1/2021

  I am building a campervan shower/mud room. Can I build the entire thing out of marine grade plywood and then paint on the redguard liquid membrane then put tile and grout on top of that? What would your recommendation be for this application?

• Steve · 3/29/2021

  Hi Jie, Thank you for your comment! Durock is a great tile backer board. I also prefer sheet waterproofing membranes over liquid. Liquid membranes can be problematic if not applied perfectly.

• jie · 3/26/2021

  Hi steve Thanks for your information. I plan use Durock cement board for my shower wall. for waterproof redgard and Kerdi membrace sheet which is better? l like sheet. thanks.

• Redblock · 2/23/2021

  Hi Ed, Thank you for your comment! I have not installed this type of panel in a shower. It looks interesting. I think it would be best to treat the walls behind the panels just like you would if you were installing tile, except you could probably get away with installing regular drywall on the shower wall studs instead of tile backer board. I would suggest that you apply a sheet waterproofing membrane (like Schluter Kerdi) to the drywall surface and simply cut the bottom of the membrane to hang just over the tiling flange of your shower base. You can create a seal between the membrane and your shower base by applying a silicon bead on the tiling flange and pressing the bottom of the membrane against it. I’m not sure I agree with the use of silicon to attach the metal panels to the waterproofing membrane. I don’t think this will work. Silicon takes forever to dry and it probably won’t stick to the membrane. I think you need a more effective adhesive like polyurethane sealant. Regardless, these panels will likely need some mechanical attachment method to keep them in place while the adhesive dries. I think this will be your biggest challenge. You should probably inquire with the manufacturer of your panels to see if they have a better attachment method than the Australian one does. Good luck with your shower! Steve

• Redblock · 2/22/2021

  Hi Skyler, Thank you for your comment! As you indicated, it’s important not to mess with the fire wall but you can attach some backer board over the Type X wall board if you use a stud finder to mark the studs and buy some longer backer board screws. You also have the option to build a new stud wall in front of the firewall if the drywall is too thick (I have seen a firewall with two layers of 1″ drywall!). If you want to tackle the job of installing a mortar base, I would suggest you look at a few blog posts and videos on the subject in order to get familiar. Just Google “dry pack shower base”. Fine homebuilding is a pretty good post that utilizes a Schluter Kerdi drain. This drain has an integrated membrane bonding flange so your under-tile sheet waterproofing membrane can bond to it. To find out more about the drain, you can look it up on the Schluter Systems website. Here’s a product that may help you create your slope. It’s called Quick Pitch. I’ve never used it but I’ve heard that it’s great for DIYers. After your research, if you’re still not comfortable tackling this kind of job, I would suggest you hire a professional to install your mortar base for you. You really need to do this step correctly. Good luck with your project! Steve

• Redblock · 2/21/2021

  Hi Ted, There a lot of people that want to avoid tiling these days because of the work, cost and maintenance so don’t feel bad! I would say that an acrylic/ fiberglass shower system does not require any additional waterproofing but a “plastic” shower kit could mean a lot of things. I have seen some plastic panel systems that glue to the tile surface of an old shower that I would not trust to keep moisture out of the stud wall because the sheets are so thin with too many joints. Installation strategy could also be an important consideration if there a lot of separate pieces where water could get through if poorly installed. Sorry I couldn’t be of more help but it’s really difficult to say without seeing it. Good luck with it! Steve

• ED · 2/20/2021

  Hi Steve, Thanks for your article. I have lots of carpentry experience but basically zero with plumbing/showers/tiling – I followed most of what you wrote (but maybe not everything, I’m still learning). My partner and I are renovating/restoring an old house/mortuary. After talking with folks and doing some research, we’ve decided to go with pressed aluminum panels for shower walls and an enameled metal shower base (Bootz showercast). I saw the comment/response about prefab shower bases, that you didn’t recommend a moisture barrier underneath. In that case, would the waterproofing just go along the walls (behind, in our case, pressed metal panels) down to the floor, meeting the wood subfloor? It seems so counterintuative! But I can appreciate that moisture could get stuck between and that could cause problems. I’ve read/seen that folks put something (like a tape, I forget what it’s called) along the tiling flange and then up and attach to the waterproof barrier on the walls (if that makes sense; to prevent any moisture that might get between the tiling flange and the tile from getting to unprotected walls/subfloor). Do you have experience with this? Also, is there a system you’d recommend over others for waterproofing behind these pressed metal panels? We’ll plan to glue them up with silicone adhesive/caulk (it will be something like this /docs/PTP-Bathroom-wet-area-installation-guide-2019-PRINT-05-2020.pdf though this is not the company we’re using because we don’t live in Australia). I haven’t been able to find much on what the best way is to waterproof behind for this specifically. I suppose it would just need to be something that the adhesive will stick to. Any thoughts would be appreciated. Thanks so much for your informative post. Cheers, ED

• Skyler G. · 2/19/2021

  Steve, thank you for sharing a plethora of knowledge and pro-tips. It makes a somewhat daunting task seem possible. I do have a couple of questions concerning my shower remodel. I previously had a fiberglass shower/tub combo that I just tore out. After getting it removed I realized that I have 5/8” Type X drywall behind one of the side which is there as a fire barrier which I can’t remove. I live in a townhome and this wall separates me from my neighbor. I’m currently at a loss on how to best approach this dilemma. Any recommendations would be great. Secondly, I can’t seem to get my hands on a Wedi or Hydro-Blok shower base. Therefore I’m planning on installing a mortar shower base. I attempted to watch a video you had linked but it’s no longer available. How would you recommend I install it and what products would you suggest? Thank you in advance!

• Ted Emery · 2/19/2021

  Sir, I am one of the minority that is not going to tile my shower, (wife hates tile). I am installing a shower kit with the rigid plastic wall panels. There is also a glass door which I won’t use. When using a “plastic” shower wall kit, is any additional waterproofing needed, or recommended, to go behind it? Thank you.

• Redblock · 2/18/2021

  Hi Robert, Thank you for your comment. I’m getting the impression that you really don’t want to take out that old shower pan. I know it’s a lot of work to remove it, but the condition of the vertical section of the old rubber membrane is not likely representative of what’s happening below the pan and around the curb. I think it would be very risky to keep it especially now that you have demo’ed the upper half of the shower. I’m not sure what the people at Fine Homebuilding were thinking but applying a sheet membrane over the tile would be a bad idea for the reasons mentioned in my post. But the solution is not to eliminate the membrane altogether and install the new tile over the old tile. Sorry for the bad news but this would be even worse than the Fine Homebuilding suggestion in my opinion. I realize that it creates a bunch of extra work for you but you’ve already got it down to the studs on the shower walls. If I was you I would rip out and start anew! Then you can do it right by installing a mortar or foam shower base (with an integrated membrane bonding shower drain) and an under-tile sheet membrane over the shower walls and base. Good luck with your project! Steve

• Robert Stephens · 2/18/2021

  This is a great web site, I’m glad I found before getting any further along with my project. I am cutting down two fully tiled shower walls to create knee walls with glass above. The idea being to make the bathroom feel bigger. I removed all the wall tiles and cement board down to the joists and am planning on installing plywood followed by Kerdi waterproofing membrane and tiles. The shower pan is”old school”with a rubber liner. It has never leaked and when I exposed the liner coming up the wall it looks and feels fine, was dry and no mold. I was planning on roughing up the existing pan tiles, installing Kerdi membrane on top and tiling over. This method was recommended in Fine Homebuilding as a method of retiling over existing shower pan tiles.The article did not address the type of pan. Now having read your advise about not installing a new undertile membrane on top of the old I was wondering if you could recommend a way of installing new tiles directly onto the existing tiles? If this could be done it would save me a lot of work. Thank you.

• Redblock · 1/13/2021

  Hi Christine, Thank you for your comment! In my opinion, installing a waterproofing membrane is the most important step in any shower installation. So I would say yes, it is definitely a big deal that they didn’t install a membrane. Unfortunately I don’t have any suggestions on how to fix this after the fact. Grout sealer is certainly not going to take the place of a waterproofing membrane, especially if there are shower niches installed. As you probably read in my post there can be problems if custom niches were installed or they were mounted on an outside wall. I’m sorry I couldn’t be of more help. Steve

• Christine Pearson · 1/13/2021

  Hello, and thank you for your definitive guide on waterproofing membranes. We recently hired a licensed contractor to remodel 2 bathrooms, one with a tub, and one with a steel shower pan. Both rooms got tiled walls in the bathing area and on the floor. We specifically requested waterproofing and have it in the contract, but for some reason their tile guy skipped it entirely, and now we have 2 bathrooms with zero waterproofing. To make matters worse, they each have a large niche. The contractor is trying to tell me it’s not a big deal, and the tile is enough protection for the walls, and suggested a grout sealer. I do not think this is adequate, but I am not an industry expert or a contractor myself. What is your advice for this situation?

• Redblock · 1/9/2021

  Hi Patrick, Thank you for your comment! As I said in my post, I prefer installing only the cement coated pans like the Wedi or Hydo-Block pan. I also mentioned that mortar does not adhere to bare polystyrene so I would not recommend that anyone install these shower pans when there are other pans available with tile bonding membranes. Schluter foam shower pans were originally bare foam but now include a tile bonding membrane on top and bottom. As far as I can tell, Prova is a bare foam shower pan. Even the coated foam pans have warnings about installing tiles that are too small. I talked about the possible reasoning for this in my Shower Membrane post. I would recommend that you follow the manufacturer’s install directions. You don’t want to take any chances. The Wedi shower system requires no membrane layers in the corners at all. With the Schluter shower system, the extra membrane thickness can easily be accommodated with a slightly thicker mortar bed beneath the tile. Good luck! Steve.

• Redblock · 1/9/2021

  Hi Mike, I have very little experience with Tile Redi plastic shower pans so I can’t really comment based on personal experience. Although it’s uncommon, the concept of using an epoxy based bonding method for tile also seems fine to me and I’ve not heard anything that would suggest otherwise. Good luck with your install! Steve.

• Redblock · 1/9/2021

  Hi David, Thank you for your comment! It’s always nice to see a detail oriented DIY’er doing their homework and trying to do it right. Congrats! 1. Ya….don’t want to mess with any structure in the slab – good call. This is a tough one and you will get many different opinions on this. I never want to go less than 2″ on any section of the mortar bed (with reinforcement) but there are guys that go thinner. I really think this is something you need to talk about with your local building authority because code requirements in many jurisdictions have not changed to accommodate the curbless shower. It comes down to a judgement call by your local building inspector so it always helps to discuss your options with them so they recognize that you are trying to do it right and not trying to get away with something sketchy. 2. As I said before, you should always talk to your local building authority about this because you can get the very best advice online and it could still be wrong according to your local code. Unfortunately, the 2″ code requirement likely refers to the top of the curb structure (with waterproofing applied). This would likely be considered as your “constructed waterproofed shower pan assembly” and it would be tested at this stage. 3. It’s great that you applied closed cell spray foam in the shower wall and ceiling. This is literally the best you can do in an outside wall to reduce the chance of condensation in this space. Spray foam is such an exceptional insulator that the temperature on the foam surface should be nearly the same as that of the tile and backer board assembly. This means a very low chance of condensation even with an above average vapor concentration. And…. NobleSeal TS is one of the best sheet waterproofing membranes out there so vapor concentration will be exceptionally low. In other words, I believe that you have nothing at all to worry about. 4. I can’t really explain what is going on in that Noble Company steam shower install doc. I guess the only way to find out is to ask the engineers at Noble Company. There are a couple great ways to install steam shower ceilings using a membrane over cementitious backer boards or simply installing steam shower rated foam board. Here are a couple of helpful links for installation of Kerdi DS and Wedi foam board installation. Good luck with your steam shower! Steve

• Patrick · 1/9/2021

  Hi, thank you for this great explanation. I’m about to install a foam shower base after removing an old tub. I’m looking at the Prova brand, wondering if you have any thoughts on their products? Also I had already bought some mosaic tile for the floor, but it’s quite small, each rectangular piece being 1/2” x 1”. You mentioned this is a no-no for the foam shower bases…is that because the tiles could compress into the foam even after the mortar sets? Lastly I’ve read that smaller mosaics can be tough to lay flat in the corners of the foam bases because of the multiple layers of membrane and mortar. Thanks!

• Mike · 1/8/2021

  Steve I’m using a shower base from a company called Tile Redi. They sent an epoxy mixture to adhere the tiles to the shower base. Have you heard of this product and would you recommend another product? Thanks Mike

• David · 1/7/2021

  Thank you for a great article and comments! Very helpful! I am replacing tub/shower with a walk in shower/steam room, using NobleSeal TS on thin bed mortar floor. I have some questions: 1) I was planning to remove some concrete and go curbless and ADA wheelchair compliant, but my slab has a post tension cable in the way and I am afraid to mess with that so I will be building up from unmodified slab. I want to minimize the curb height. What is the minimum thickness the mortar can be and still be strong enough? Any recommendations for minimizing curb height much appreciated. 2) Code says waterproof curb must be 2″ above drain. Why? How is this code accommodated with a curbless entry? Also, is it 2″ to top of waterproofing of curb structure or to top of 3/4″ thick marble threshold which will have 100% silicone bead to NobleSeal TS on curb? I would like to build a mortar curb the same thickness as the mud bed and put the marble threshold on top as this is as close as I can get to what I was planning with curbless entry. 3) I am planning on fully filled closed cell spray foam in all walls and ceiling but this is also a vapor barrier. Does this create a hazardous vapor barrier sandwich or a void where condensation can occur between insulation and cement backer board? 4) NobleSeal TS instructions say for steam room to sandwich TS between two cement backer boards on ceiling. This makes no sense to me as I don’t see how this forms a vapor barrier since it will have many screws perforating the TS. Can you explain what is going on with this? See /docs/STEAM_SHOWER-ROOM__NOBLESEAL_TS.pdf

• Redblock · 12/21/2020

  Hi Rich, Thank you for your comment! I understand your dilemma. When joining the Wedi shower board to your Schluter shower pan, it’s a bit confusing because the two products use different techniques to seal the corners and margins. Wedi uses their Wedi joint sealant and Schluter attaches their Kerdi band with thinset. Personally, I would use the Wedi approach for the corners. You are already using the Wedi joint sealant to join the Wedi wall panels together and for covering the screw holes. I would also apply a 1/2″ bead of sealant to bond and seal the Wedi panel to the Schluter shower pan. I would then apply the Wedi sealing tape on the joint using the Wedi joint sealant instead of thinset. It’s a great idea to apply the Kerdi membrane (or Wedi Subliner Dry) to your mud pan extension but you don’t need to wrap it up the wall. You can just use the Wedi joint sealant and sealing tape on these corners as well. Just make sure you are applying the joint sealant to the mud extension after the Kerdi has been applied and the thinset has set. If you are uncomfortable joining the corner tape to the Kerdi base with Wedi sealant, you can attach this side with thinset if you prefer. You can see the technique I’m suggesting in this Wedi sponsored video. The last 1/3 of the video shows the corner tape attachment. Good luck with your project! Steve

• Rich Keeler · 12/21/2020

  I have installed a schluter shower base but have Wedi walls. What is best way to waterproof the wall/base joint. Figured the schluter band but do I use modified thin set or unmodified thin set on both the schluter base and wedi walls? I did have to extend the shower base with a mud bed and figured I would cover with kerdi sheet. Can this too be wrapped up the one wedi wall

• Redblock · 12/6/2020

  Hi Ali, Thank you for your comment! If you’ve purchased your acrylic/fiberglass shower base from a reputable manufacturer (like the ones you mentioned) and it’s installed correctly, you should not have to worry about it cracking. Eventually the surface will become faded and somewhat brittle, but I have seen these types of shower pans last for decades with no problems at all. That said, I have seen these shower pans crack and leak when they were installed incorrectly. For example, because the tiling/ mounting flange is attached firmly to the wall studs, these bases will definitely crack if your subfloor deflects even a tiny amount….. so make sure the subfloor under the pan is rock solid! Many times I’ve also seen these pans leak around the drain simply because the drain assembly was not attached firmly to the pan. Personally I would not be concerned about waterproofing under the shower base. This is not a standard practice because these assemblies are designed to last for many years without worry. If the worst case scenario happens and your shower base cracks and leaks, it will likely be a slow leak that you will identify soon enough. In fact if you would waterproof the area beneath the pan, water would pool below the pan, possibly causing bigger problems when this water escapes. I hope that helps. Steve

• Ali · 12/3/2020

  Hello If I were wanting to install a prefab shower base (Delta, Kohler) is there an underlayment that should be put below the shower base? A Kerdi membrane? Vinyl water liner? I’ve heard so much about pans cracking especially acrylic so I’ll try my best to find something more durable but in the worse case scenario it cracks how to mitigate the water that leaks…and make the floor more waterproof before installing the prefab shower base pan/tray Thank tou

• Redblock · 10/31/2020

  Hi Jim, Thank you for your comment. I’m not really sure what product you’re referring to but the USG Durock sheet waterproofing membrane that I’m aware of is attached to the substrate with unmodified thin set mortar. Here is the USG Submittal Sheet for this product. If you are referring to another USG product that I’m not aware of, I’m sure a local USG rep would be happy to help you out. Good Luck! Steve

• Jim McClelland · 10/31/2020

  Hi Steve, I have some leftover Durock Tile Membrane (two or more rolls) from a couple of projects. I would like to use it but the adhesive is no longer available. Is there a suitable adhesive that will give me the same great results? Jim

• Redblock · 10/22/2020

  Hi Dona, Thank you for your comment! Firstly I have to admit that I have absolutely no experience with this type of installation. It makes some sense that vinyl floor planks could be used to create a “waterproof” shower wall, however I think it would be naive to assume that there was no risk to this install. For starters, you have to be pretty certain that the adhesive that you choose to join these boards is appropriate for the unique stresses of the shower environment. As well, I think that these panels have an air space in between the top and bottom layers. I would wonder if this might accumulate condensation and eventually mold……. it would really depend on how permeable these planks are. Remember that there is no such thing as a truly “moisture-proof” material. As for your choice of backer boards, this also depends on how permeable the vinyl is. I would assume that the permeability is very low so backer board choice (or waterproofing membrane for that matter) would not be that important, but that is just a guess. I’m sorry I couldn’t be of more help. It’s just a bit too unconventional for me to be qualified to advise you on this. But I sincerely hope that it all works out for you! Steve

• Dona Mapston · 10/22/2020

  Hi Steve Great and informative article – thanks! Long question here but we doing something unconventional so I want to fully explain. We are remodeling (DIY – we are moderately experienced) our master and putting in a large walk-in shower where the tub used to sit next to the current small “normal” square shower. We’re going to take advantage of the fact that we already have drain plumbing from the original shower to remake that space as a drip-dry area at the new shower entrance and use a teak shower floor mat there. We have yet to rip out the current shower so not completely sure of the condition of the concrete slab under there but it was new construction 15 years ago so hopefully in good shape as the is the slab area under the old tub/new shower space. We are currently planning to red guard under the teak mat but we’ll assess after the tear out. We are strongly considering using a hydro blok shower base as the walk in will have an odd shape (old tub was corner roman) and we like that the hydro blok can be cut to fit easily. We are going to be using large flat cut river pebbles for the shower floor ( properly sealed of course). The walls however will be somewhat unconventional although we are reading about more folks going this direction: we will be using waterproof luxury vinyl planks. We will be additionally sealing all the plank seams as they are installed. With this in mind we are wondering about the denshield we were planning to use for the wallboard – you mention in a comment above that denshield does not have a good perm value and recommend red guard over top. Since we are not going to have permeable tile/grout but instead a waterproof vinyl surface is this still something we would need? Also, based on our plans are the other factors we should be aware of that you can imagine? TIA!!

• Redblock · 10/16/2020

  Hi David, Thanks for your comment! It’s great to hear from a fellow tradesman. I applaud your innovation. These are things I have also considered many times in order to save a bit of money for the client, but still maintain the integrity of the entire assembly. As you probably gleaned from my post, I think the Wedi pan is the best because of its cement coating. Hydro-Blok is another (slightly cheaper) manufacturer of cement coated pans but they have limited distribution in the US for some reason. Perhaps this suggestion is a bit obvious but if you’ve not already tried this, you should first attempt to open a trade account with one of the local tile suppliers. I realize that you are a mason and not a tile setter, but as a business owner I believe they would grant you a trade account. The discount may not be huge on your first purchase but I recently received 40% discount from a supplier that I’ve never done business with before and they didn’t even check my references. This might tip the scales in your decision about the Wedi pan! Regarding your technique of taping & Redgarding your seams…..Whether you extend your pan or not, I would suggest using a slightly different approach on the pan transitions because pan transitions are more vulnerable than wall seams. You would need to buy a roll of sheet membrane seam tape and the adhesive joint sealant to attach it. You don’t necessarily need to get this brand but the technique is sound. The exact technique I’m suggesting is shown in this Wedi video. (Make note of the pan to wall transition). I think Durock on the walls would be great and your Redgard idea would also work very well. The only modification to this would be my suggestion above for the seams/ transitions. I know that I mention that I don’t like mixing products/brands, but I think this particular technique would work well in your situation. One last thing….. I have not used KBRS products before but I believe that they make custom size shower pans and their pricing might be better than Wedi. And they also seem to put a bit more effort into reinforcing the upper (tile bonding) layer than other pan manufacturers and that can only be a good thing to reduce point source compression risk. I really hope that helps, and good luck with your project! Steve

• David Atilho · 10/16/2020

  Hey Steve, We just bought a home that needed extensive remodeling. 2 of the 3 bathrooms were easy rip and replace alcove tubs. I used regular Durock, sealed the seams with tape/mortar, and 2 coats of red guard (3 on the screws and seams). Now for the Master Bath… I have multiple sheets of the duraock left over and plenty of red guard (purchased the 3.5g bucket). I am a mason and had planned on doing the shower pan the “old school” way until my plumber suggested use of the Preslope. After about of week of research (your article being very helpful) I think I’m ready to purchase one. I’m torn between wedi, hydro ban by laticrete, or KBRS. Issue I am having is finding a 42”x60” with a linear drain. 36” seems to be most common. I’ve seen dry pack extensions to the standard foam pans but can you extended one such as the hydro ban one. My initial assumption would be to tape the seam and red guard it, but it seems like your not a fan of mixing products/brands. If I so happen to find one to size (hrydroban has a 44”x72” I’m hoping I can trim depending on if the linear drain allows). Wedi has one in the size I need but it’s $1200!! So options are to get a standard 36”w and extent to 42” if you think my method of redguarding the extensikn works, trimming the 44” hydro ban down to 42” or worst case splurging on the wedi. Once the pan is figured out, is it possible to use standard durock on the walls, adhere/seal the first sheet where it meets the pan, taping the seams, and finally 3 coats of red guard? I know I’m trying to get a little creative to be cost effective and use the leftover product I have. Any suggestions concerns with my madness?

• Redblock · 9/15/2020

  Hi Denise, If you’re referring to the prefabricated foam shower trays, then the quick answer is yes! You should download the shower tray brochures from Durock and Wedi to see what sizes they offer and the different drain positions. If your shower size does not conform to these standard sizes, they also offer extension pieces that allow you to extend the length or width of these bases. This is super easy but is also fairly expensive. A much cheaper way to extend one of these bases is with dry pack mortar. This is usually a job for a professional, but if you do a bit of online research and you’re motivated, you could easily do this yourself as well. Here is a video I found online that shows this type of tray extension using a Schluter Kerdi shower tray. The process would be the same no matter what tray you install. Let me know if you need anymore info. Good Luck! Steve

• Denise · 9/14/2020

  Hi there, I have a particularly large shower 75×48 does Wedi or Durock come in a variety of sizes? thank you

• Redblock · 9/7/2020

  Hi Ramon, Thank you for your comment! I have not used the Proflex waterproofing membrane products so I can’t really comment on how they install, or how effective they are. One thing that does concern me though, is that they don’t seem to mention anything about perm ratings of either of these products. Maybe I just missed it, but every company that makes a waterproofing membrane should make these ratings very clear in their specs and promo materials. These guys have dropped the ball in that regard. There are plenty of great membranes to choose from out there. You don’t need to take chances with those that don’t want to publish their perm ratings. Just my opinion. Good Luck! Steve

• Ramon · 9/6/2020

  Do you know much about proflex products they seem to offer a product similar to this they are a company out of florida both a liquid and sheet product for waterproofing. Im getting ready to remodel my master bathroom?

• Redblock · 8/24/2020

  My pleasure! Good luck with the repair! Steve

• Debra B · 8/23/2020

  Thank you so much, Steve, for this information. The tiling has not been installed, so it is better to find this out now than later. Very grateful!

• Redblock · 8/23/2020

  Hi Debra, Thanks for your comment! As you probably already know after reading my blog post, I’m not a fan of the “old school” mud base with liner. That said, you may still be ok with a Redgard coated mud base and curb, even with the penetrations in the liner. The thing is…..the traditional mud base was never intended to be covered with a sheet or liquid waterproofing membrane. This has always been a stand alone “waterproofing” system. The introduction of a “undertile” membrane confuses matters significantly because it combines two incompatible systems (as I mentioned in my post). The Redgard membrane may very well prevent moisture from getting through your compromised shower curb (with adequate thickness and corners taped), because that’s what it was designed to do. This however, is not your only problem. The bigger problem is that a “undertile” membrane will only work optimally if it’s installed without the pan liner and with a compatible “membrane bonding” drain assembly. The perimeter of the drain will still not be protected from moisture infiltration because it was never designed to do this. Here is a good article describing the differences between the two systems in detail. The bottom line is that your shower base has not been built correctly according to either of the two systems. So if I were you, I would remove it and start over. But if you are not in a position to do this, you could consider altering the traditional “clamping drain” with an adapter kit that would allow it to be compatible with the Schluter Kerdi sheet membrane (described in the link above). Just keep in mind that this will not correct the problem entirely. Sorry for the bad news. Good Luck! Steve

• Debra B. · 8/22/2020

  Thanks for this blog! So we are in a bind. We are getting our shower rebuilt. The new pan had been installed. The mortar on the shower floor had been installed. The tiler came in and put screws on the top of the curb and the inside side of the curb in order to secure the cement board on top of the liner . We did not notice this until two thin layers of red guard had been painted over them. But hubby noticed and we freaked out because putting holes in the liner, especially on the inside of the curb, we had been told by many folks is a total no-no. When we asked the plumber, he said he would not warrant the work any longer; his pan had been compromised. The Tile guy said that the liner had not been properly glued in, so screws were necessary. He claims that that’s what red guard is for, to waterproof the screws, and that the curb is good. Now we are torn. Red guard is there so it should be sealed up. Surely it won’t cause problems. And yet … Should we just go with the curb as is, or should we tell the tile guy to rip it out and redo? Thank you (from people too long without a shower now…)

• Redblock · 8/5/2020

  My Pleasure! I hope it all goes well. Steve

• Dees · 8/5/2020

  Thanks Steve. I spoke to the contractor and he says his sub will be using the Hydro Ban Sheet and that they are very experienced in using the different Laticrete products. Thanks for having this blog that being so responsive.

• Redblock · 8/3/2020

  Hi Dees, Thank you for your comment! Hydro Ban liquid membrane is generally a good waterproofing membrane. I would only be concerned if one of your shower walls is an outside wall and the stud wall is only 3 1/2″. If so, moisture will likely condense in this wall in the winter months if you use a lower Perm liquid membrane like Hydro Ban. In this case I would generally recommend one of the sheet membranes with the higher perm ratings. Hydro Ban Sheet Membrane has a .06 perm rating which is extremely good. I would recommend this product wholeheartedly, as long as your contractor is comfortable installing it. Good Luck with your project! Steve

• Redblock · 8/3/2020

  My Pleasure! Glad I could help! Steve

• Dees · 8/2/2020

  Hi Steve, Learn a lot in reading this blog. My bathroom remodel will be starting shortly and my contractor use Laticrete Hydro Ban. As I was not familiar with it I decided to do some research and came across your blog. Given that Hydro Ban has 1.25 perm rating, would the Hydro Ban Sheet Membrane be a better option to waterproof a shower providing the contractor has a lot of experienced installing the Hydroban Sheet Membrane? As this is not a steam shower, is there a minimum perm rating recommended for waterproofing a standard shower remodel?

• Nathan · 8/2/2020

  Thanks so much Steve! I’ve decided to use only a kurdi waterproof membrane. Thanks again!

• Redblock · 7/31/2020

  Hi Nathan, Thanks for your comment! As I mentioned in my response to a previous comment, I do not recommend installing two different waterproofing membranes over each other. The results are too unpredictable. If you want to improve the perm rating of your Redgard installation, you should simply apply another coat. I would also make sure the corners and joints are taped. Good Luck! Steve.

• Nathan · 7/31/2020

  Hi Steve, thanks for the informative article. I currently have a drywalled shower/tub surround awaiting tiles. I’m wondering if I can use redgard liquid membrane on the drywall AND a waterproof decoupling sheet on top of that. Would this create a moisture sandwich or is it safe to use both on the walls? Thank you

• Redblock · 7/30/2020

  Thanks Kimberly. I’m happy that you found it useful. Steve

• Kimberly · 7/30/2020

  Hi Steve, thanks very much for your detailed explanation. Greatly appreciate it! Kimberly

• Redblock · 7/29/2020

  Hi Kimberly, If your shower valve is what caused the leak, that’s a whole other thing! That means that your waterproofing may be all good. But I can say from my experience that even two cracked tiles could be an indication of something nasty going on beneath you base tile. The safest route would be of course to replace the entire shower surround and shower base. But if a full remodel is not currently possible, the first thing to try is to fix or the valve leak problem of course. I would then open up the other side of the valve wall and rent a drying fan to thoroughly dry the stud cavity (only warm air, not hot). This will also help to dry the moisture from the mortar base if water has collected on the inside of the rubber base liner (if there is one). Even if there is undertile waterproofing, this procedure would also be a good idea because everything must be thoroughly dried out inside and outside before any other repair measures are done in the shower. I would then simply re-caulk the corners with silicon (after it’s super clean and super dry) and seal the entire shower with a good stone/tile/grout sealer. This is not a waterproofing membrane because there is no such thing, but a good sealer will limit moisture transmission into the base and walls. That is the best you can do without a full remodel. I would NOT remove the shower base tiles and attempt to install a waterproofing membrane. Anybody attempting this will only make your shower worse, not better. Waterproofing membranes are integrated systems and must only be installed during a full remodel. The shower base could also be irreparably damaged. Unless the cracked tiles are loose, I wouldn’t try to replace them either. Good luck! Steve.

• Kimberly · 7/28/2020

  Hi Steve, thanks for your quick response! Your explanation is much appreciated! I just wanted to clarify that the leaky shower is due to a ruptured shower mixer. I do not know the current state of the waterproofing membrane under the tiles at this point. I received different pieces of advice: (1) Replace the shower mixer, then apply clear waterproofing membrane over the tiles; and (2) remove and retile the entire shower, like what you suggested above. Given that the leak was caused by the shower mixer, would you still recommend to rebuild the entire shower? Or, will replacing only the floor tiles (i.e., not the three walls), along with undertile waterproofing membrane, solve the issue? Many thanks again! Kimberly

• Redblock · 7/28/2020

  Hi Kimberly, Thank you for your comment! I must give you credit for an innovative solution…..but, I think this would be a bad idea. You may very well stop the leak into the ceiling below by using your innovative approach, but the leak itself is not the only problem at this point. The bigger problem is that the waterproofing membrane has failed, and it’s very likely that there’s already a significant amount of moisture (and mold) within the shower base assembly. It is also more likely that there is no waterproofing membrane under your shower base tile. It’s more likely that you have a traditional mortar base with a rubber membrane beneath. These old school “waterproofing” systems were very often installed incorrectly causing breaches in the rubber membrane. And if by some small chance you do have an undertile membrane, it was obviously installed improperly and will be impossible to repair just by removing the shower base tiles. In other words, this would be another really bad idea. Bottom line is…..if you try to seal the top surface of the tile you will be locking in the moisture that lies between the tile surface and the rubber membrane. This is a terrible scenario in the long term. It means that mold growth could continue unchecked, which could eventually expose you and your family to toxic mold spores. Sorry for the bad news, but I think that your only viable option is to demolish the entire shower and start over. And make sure a well rated undertile waterproofing membrane is installed this time. Good luck! Steve.

• Kimberly · 7/28/2020

  Hi Steve, Many thanks for this very detailed and helpful post. Given your extensive knowledge, I wonder if you are able to comment on the effectiveness of a clear waterproofing membrane over (rather than underneath) shower tiles. Is this something you would recommend? I have a leaky shower and mold/stain has developed on the ceiling directly below it. I was advised to remove the floor tiles (still in good condition, except for two cracked tiles) and replace the waterproof membrane underneath. This process seems time-consuming and costly. Do you think transparent waterproofing over existing tiles work just as well (if cracked tiles and/or gaps are all sealed up)? Will this be a good solution? Thanks very much in advance for your help. Kimberly

• Mark · 7/19/2020

  Great info. Will do. Thanks Steve!

• Redblock · 7/18/2020

  Hi Mark, Thanks for your comment! You should definitely fill the new hole in your slab with concrete because you need reliable and solid support beneath every square inch of those foam shower pans. Here’s how to do it correctly – First drill a few holes around the perimeter of the new hole that you created so you can insert rebar for support. These can be 3/8″ diameter, drilled parallel to the floor, at least 3-4″ deep, centered in the slab, about 10″ apart. Then insert short lengths (6″-8″) of 3/8″ rebar into the holes. These will serve to “connect” the original slab to the new concrete you’ll be placing. It also be a good idea to suspend some wire mesh between the rebar if the hole is bigger than 2 square feet. After you’ve roughed in your new shower drain, mix some “dry pack mortar” to fill the hole. I would not use regular concrete mix because it contains too much water. You should be able to find several good posts online about mixing dry pack. It’s super easy, kind of fun, and will be super strong when cured. The fact that you will be covering this “fresh concrete” with a foam shower pan may seem counter-intuitive but I can assure you that it’s all good. In fact, concrete (and dry pack mortar) cures much better in the presence of a small amount of water. I can stay “hydrated” for years and it will only become stronger. Any residual moisture will eventually dissipate downward and sideways throughout the slab equalizing the moisture under the pan. Here is a great video by Schluter Systems showing the placement of dry pack mortar around a Schluter Kerdi drain. But unlike the video, I would recommend that you place the rebar supports, especially if the hole is larger than that in the video. Good luck! Steve.

• Mark · 7/18/2020

  Hi Steve, Thanks so much for this great post. I am converting a tub to a shower. It is on a concrete slab. I plan to use a Kerdi or Wedi shower pan. I need to break up and remove the concrete to move the drain. Once I have moved the drain I assume I need to refill and pour new concrete in the area where I removed the concrete. I read that concrete takes at least a month to cure, during which time it is giving off water. So: do I need to wait a month before I put the shower pan down so I don’t have water buildup between concrete and shower pan? Alternatively, could I just fill the hole in the concrete with gravel and put a sheet of plywood down before putting down the shower pan? Thanks very much for your help. Mark

• Adel · 6/24/2020

  Hi Steve, thanks for the prompt response! I’ll definitely do that then, especially since the tiles we are going with are all ceramic and not porcelain. I know there’s a lot of competing factors that go in to deciding how to proceed, but I do very much appreciate how well you distill the information to make easier for us understand. Thanks again! adel

• Redblock · 6/24/2020

  Hi Adel, Thank you for your comment! It is true that the manufacturers of Densshield mention very clearly in their product documents that you do not need to apply a waterproofing membrane when using their product. However, Densshield has a perm rating of 1.5, which is not adequate as a shower wall waterproofing membrane, in my opinion. By contrast, Schluter Kerdi has a far superior perm rating of .75 which I consider to be a minimum requirement. As I mentioned in my waterproofing membrane post, I would instead prefer to use their Kerdi DS or the other ultra low perm, sheet waterproofing membranes. So to answer your question……. Yes, I would suggest that you should indeed apply two complete coats of RedGard in order to establish an adequate perm rating. I believe that this extra step is ABSOLUTELY necessary in your current situation. There is a lot more that I could say on the subject, but I will leave it at that for now. Please let me know if you have any follow up questions. Good Luck! Steve.

• Adel · 6/23/2020

  Hi Steve, this post (and your blog in general) is super helpful. One question I had for you based on this article is that you mentioned that you would not use DensShield as is as your water proofing membrane layer on the wall. My contractor has just installed DensShield backers and used RedGard over the screws and all the seams. I suggested that we just go ahead and roll all the walls, and he said that it’s not necessary b/c the warranty on DensShield doesn’t require additional waterproofing. What do you think? I lean towards just putting a full (or two…) on since you already are covering ~25% of the wall just sealing the screws and corners/seams. I’m not opposed to doing it myself if he doesn’t want to but don’t want to push it if it really isn’t necessary. Thanks! Adel

• Redblock · 6/15/2020

  Hi EG, Thank you for your comment, I’m not sure I’m understanding your situation correctly, but I’m assuming that your contractor went ahead and installed the RedGard without knowing that you actually wanted Shluter Kerdi installed instead. If this is the case then I would recommend that you not install the Schluter Kerdi over the Redgard. If you laminate these two layers the result is too unpredictable. I would be worried about water vapor accumulating between the RedGard and Kerdi. A better idea is would be to get your contractor to roll on another layer of RedGard if you wanted the additional protection. Only if you remove the RedGard entirely, would I recommend installing the Kerdi membrane. If you do this, you should not paint any RedGard over the seams. The Kerdi seams are supposed to be covered with Kerdi Band and the corners with Kerdi Kereck. Make sure your contractor follows the installation instructions for these products. Good Luck, and let me know if you have anymore questions! Steve

• EG · 6/15/2020

  Your article was great! I am redoing a bathroom and the cement board has red guard on it and I was planning on using the Kerdi membrane is this going to be a problem? Also someone else had suggested that after all the Schluter membrane was installed to also use a bit of the red guard over all the seams. Is this a good idea? or not? Will it hurt or compromise the Kerdi? Time is of the essence . Thank you! EG

• Dustin Shoaf · 2/24/2020

  Steve, Thank you for the feedback. I have actually already added blocking to the joists and even added some sister joists. I was unsure if I can include the 1/2” cement board under the Schluter pan so thank you for clarifying. Thank you again for timely response. Much appreciated.

• Redblock · 2/24/2020

  Hi Dustin, Thank you for your comment. Sounds like a fun project! Yes, 3/4″ T&G ply is pretty typical for a subfloor so you’re definitely on the right track, but I do have a couple of suggestions. Now that you have the joists exposed, I would install some bracing between the joists before you install your ply. You can install X bracing or solid bracing (blocking) to accomplish this but solid bracing is much better as long as you use the same dimension lumber as the joists (2″x10″‘s most likely). These braces are simply attached between each joist to reduce deflection in the floor (make it more rigid). Just Google “Joist bracing” and you’ll see exactly how to do it. I would also suggest screwing and gluing these braces in place using construction adhesive and framing screws. This will reduce movement and further stiffen the floor assembly. I would also attach your 3/4″ ply with screws and again… construction adhesive applied to the top of every joist. It also wouldn’t hurt to apply your 1/2″ cement board under the Schluter shower base as well, since you’re applying it on the rest of your floor anyways. A super solid subfloor beneath your Schluter shower pan is actually more important than the rest of your floor because of the immense amount of weight on this part of the floor after the shower is fully installed. Just make sure you attach it to the plywood with the thinset method, and the recommended amount of screws, to eliminate voids between the ply and backer. Again, all these steps will help reduce deflection in your subfloor which is by-far the most important step if you plan on laying tile. Let me know if you have anymore questions and Good luck with your project! Steve

• Dustin Shoaf · 2/24/2020

  Great article. Very informative. I have our bathroom down to the floor joists and wall studs. Doing a full makeover. Converting a shower tub to a tiled walk in shower. Will also be tiling the floor. I plan on laying down 3/4” tongue and groove subfloor over the whole bathroom. My understanding is that I can then lay down a preformed shower bed from Schluter directly over the 3/4” subfloor using thinset. However, when tiling the rest of the bathroom floor, I need to also lay down 1/2” cement board before tiling. So basically the shower pan will be 3/4” subfloor, Schluter preformed bed pan, then tile. The bathroom floor will be 3/4” subfloor, 1/2” cement board, tile. Is that appropriate to do? I plan on using a Schluter preformed curb and half wall.

• Redblock · 1/17/2020

  Hi Claire, Thank you for your comment! Aluminum does not rust as iron products do. Bare (unpainted) aluminum will darken when exposed to water but if the finish is powder coated with a high quality paint finish, the surface should be durable and last for many years. But that is assuming the powder coated color finish stays attached to the aluminum (only time will tell). A completely sealed solid aluminum frame would indeed be completely waterproof similar to a solid stainless steel niche however, the Kohler pilaster has a cap that attaches to the top of the niche frame. This is a big concern for me since this could allow water vapor to enter the stud cavity. This would NOT be good….. especially on an outside wall. If moisture makes it into the stud cavity, it could easily condense on the back side of your niche and cause mold growth. Another problem with the Kohler Pilaster (in my opinion) is the fact that it does not bond to the shower wall waterproofing membrane. This niche, like many other finished shower niches out there, is a retrofit shower niche. This means that it is inserted into a hole in your shower wall after the wall has been tiled and grouted, with only a bead of silicon sealant keeping moisture from entering your stud cavity. This is not an adequate waterproofing measure, in my opinion. A silicon bead attached to the tile surface can allow water vapor to enter the stud cavity even if it’s properly applied…. and if this flimsy seal breaches, liquid water will enter this space. Sorry for the less than good news but I think it’s important for you to know the straight goods on finished shower niches. The are definitely not all created equal. Good luck with your project! Steve.

• Claire Grace Armitage · 1/16/2020

  Great and timely find. Thanks for all your information. I am in the process of taking our bathroom back to the studs and was getting ready to push the “buy” button for the Kohler Pilaster Shower Locker when I found your site. I like how narrow and tall it is, but it will be on an outside wall. You speak about stainless steel shower niches in your article…the Kohler product is aluminum. Will aluminum function in the same water tight way as stainless? Does aluminum rust? I live in Northern California. The winter temps can fall into the 30s and the summers the 90s, though the temperature in the house stays pretty constant because of our foam roof. What do you think about the aluminum? Thanks, Claire

• Redblock · 11/15/2019

  Hi Francois, Thanks for your comment. Although the screws would indeed penetrate the membrane, the proper screws (with gaskets) are designed to keep out water. I would imagine that they would do a pretty good job in a high moisture environment like the shower as well. I would still try to keep the number of attachment points to a minimum. However, with corrugated metal on the shower wall, I would be concerned about water vapor moving behind the metal via the raised sections (corrugations). You may think that a small amount of water vapor here might be OK because there’s a waterproofing membrane protecting the wall from moisture penetration, but it kind of defeats the purpose of using a product like corrugated roofing (unless you are saving a bunch of money). The raised sections work well to allow air to move up the roofline but they are probably not a good idea in the shower. Since this product was not designed for a shower, there are possibly some risks that are difficult to predict. For instance, if you don’t have adequate insulation in your outside stud wall, you may be creating a condensation surface on the face of the membrane because of a temperature differential. I think it could work quite well if the corrugations did not allow air to move up behind the panel. Perhaps if they were filled with polyurethane foam somehow. Just a thought. I admire your willingness to try something different (and kind of cool!) but I would not try it myself. Good Luck with it! Steve.

• François · 11/14/2019

  Steve, thanks so much for this long but very thorough article! Great job boiling it all down. I am considering using corrugated metal on my shower walls instead of tile (it’s a thing!) but since it is screwed to the backer I am concerned about all the penetrations through the membrane. Any pro tips to offer?

• Redblock · 11/10/2019

  Hi Doug, Thanks for your comment. It’s much appreciated. I’m so sorry I did not respond earlier. Yes, I think you are right about all of us getting used to the concept of “decoupling” a tile assembly from the substrate, however it is also a good idea to be critical about the performance of any product you buy, especially if you discover peculiar performance like you and James did. As I mentioned, I have never performed this kind of test on the Durock membrane, so I was not aware of this strange performance. I will put aside some time to try this test myself. Regardless of what the Durock rep claims, it seems sketchy to me. I have tried to remove porcelain tile (set with modified thinset) from Schluter Kerdi and it wasn’t easy at all. Let me know how it turns out, and I will try to update my Shower Membrane post soon with my new findings. Steve.

• Doug · 11/1/2019

  I also went with the Durock shower system and got the same results as James. I even burned/back buttered some mortar into a small test strip of membrane and got the same results. I talked with USG and they indicated this was normal. They even said the membrane could be used on a ceiling. I was thinking of doing this, but I do not think I will. Dont have a warm fuzzy feeling after seeing it peel. I think you hit the right water to mortar ratio when you mentioned the “definition of proper adhesion” Steve. Ive been struggling with this for a few days. Ive seen smilar online posts indicating it is ok if it stays on the wall and peeling is different than the forces the tile will generate. Im thinking this new technology will need some getting use to. It goes against normal reason that a membrane can support tile that peels away from the mortar. But I quess what you are saying is thats what makes it an uncoupling membrane. I think I will give er a try. Thanks for this post.

• Redblock · 10/2/2019

  Hi Art, Thank you for your comment and your compliment! Correct! I would NOT use any vapor protection behind the Durock backer board. BUT, if it’s an outside wall, make sure there is at least 5 1/2″ of insulation behind the backer board. Install a good sheet style waterproofing membrane (.2 perms or lower – Wedi Subliner, Durock Membrane, NobleSeal TS …) over the Durock tile backer board (under the tile). I would also get some of the alkaline resistant fiberglass mesh tape (grey color – in same section as the backer board). Before applying the waterproofing membrane, tape the backer board seams and cover with a very thin layer of thinset (no bumps!). I always use Mapei Flexcolor CQ premixed grout. It’s a bit more work to apply but it’s awesome. Unlike other premixed grout, this stuff dries hard as a rock and is water sealed. I include a bunch of Flexcolor grouting hints in my Shower Tile installation post. Another great thing about Mapei is that they also carry a full line of pure silicon sealant that’s color matched to all their grout. By far the best type of tile for showers is porcelain because it’s much more moisture resistant than Ceramic. Again, I’ve got a bunch of tips in my Ceramic or Porcelain post. Good luck and have fun with your project! Steve

• Art · 10/2/2019

  Steve, well written article with very good information – thank you for doing this! So I’m in the beginning stages of a DIY bathroom remodel. Originally to tile an alcove tub /shower enclosure I was planning using 4 mil plastic barrier, 1/2″ durock, and then the tile. If I understand your recommendations, the correct materials would be 1/2″ durock, some form of membrane, and then tile. Correct? If so, what about seam sealing the durock? If so what is the recommended technique? Also any thoughts about grout – preferences and which is longest lasting and waterproof? Any types of tile to stay away from? Thanks again. Nice work.

• Redblock · 6/20/2019

  Hi James, It does seem quite baffling. You didn’t mention if you tried a modified mortar after you tried the unmodified. Although the unmodified should work according to Durock, I would have only used a modified mortar since the polymers would definitely help with adhesion (and Durock doesn’t prohibit their usage). I don’t really have a favorite brand but I have used several of the Mapei mortars and Schluter All-Set. Honestly, I’m wondering why you tested the membrane’s adhesion after the mortar was dry. I would only do this if there were clear indications of delamination, bubbles etc. You should probably ask a Durock rep about your experience, but it sounds to me like you used an adequate mortar, mixed it well, and ensured proper wet coverage. That’s really all you can do. Maybe the problem lies in your definition of proper adhesion. Perhaps a Durock Rep would indicate that the membrane is supposed to peel off this way after the mortar dries, and this behavior does not represent inadequate adhesion. That’s only my guess, but I do think you should talk to someone at Durock that could answer technical questions about the Durock shower system. Sorry I couldn’t be of more help. Good luck with your investigation, and your project! Steve

• James · 6/20/2019

  I decided to go with the durock shower system for my upgrade. The problem I’m having is I cant get the sheet to adhere properly to the unmodified mortar. After 48 hours I can peel it off like a sticker. I tried a couple Mapei thinsets, the latest being the uncoupling membrane one. I mix for 5 minutes at no more than 500 rpms, let slake for 10 minutes and used the higher end of the water spectrum. Used recommend trowel and everything. Coverage is well over 95% as all the peaks are collapsed smooth as silk. Still, will not bond. Thinset is ANSI A118.1. Any advice? Is there a specific brand thinset I should use?

• Redblock · 5/27/2019

  Hi Clay, Thanks for your comment and your suggestion about CIM 1000. I agree that this is a good product with it’s crazy low perm rating (.03 perms). I really didn’t have the space to mention every type of waterproofing product so I left out a few 🙂 . Like you, I’m definitely biased towards the lower perm membrane products (like CIM 1000), but I’m also biased towards sheet membrane products over liquid, because their perm ratings are generally better (aside from the CIM of course). I agree with you that this product is a little expensive. I also think it’s a little overkill. The two top membranes I recommend, the Wedi Subliner Dry and the Durock Waterproofing Membrane by USG, have .05 and .079 perm ratings. These ratings are already considered overkill by many professionals because they are much better that the required threshold of

• Clay · 5/25/2019

  Why is it always redguard and other DIY products. I use CIM 1000 for shower pans and walls, and nothing comes close to it. It is way stronger and longer lasting than redguard, and tougher than any system mentioned here. They use this stuff in industrial water systems, and it is safe in drinking water. Also no VOC. Maybe it is rarely mentioned because it is very expensive at 125.00 bucks per gallon, but you can find it in most waterproofing construction suppliers.

• Redblock · 4/27/2019

  Hi Ralph, Thanks for your comment! To be honest I am not too familiar with GoBoard because I have not used it in any of my installations. According to the specs, it appears to be a different kind of product than other foam boards (different kind of foam). It is apparently designed to carry loads (can be installed on floors) and they make it clear that it is NOT an extruded polystyrene product like other foam boards. In other words I would need a bit more experience working with it to make any comments about it. However, I did notice that it is not recommended for installation in steam showers because it has a perm rating of “

• Ralph Pond · 4/26/2019

  I note you do not reference Johns Manville GoBoard in your discussion of Foam Shower Wall Panels. With joints and screws sealed with urethane rather than patches adhered with thinset, and no washers required, the GoBoard system seems it would be easier and less expensive to install than its competitors. Do you have concerns about the integrity of the GoBoard wall panel system?

• Redblock · 4/6/2019

  Hi Charles, Thanks so much for your comment. I’m not surprised that you’re a little confused. The manufacturers always seems to leave out some critical information when describing their products. Perhaps I may have provided some conflicting info as well. I apologize if I did. I will go over it again and fix it if that’s the case. 🙂 To answer your question…. a waterproofing membrane is indeed required for the Durock shower tray. This is one of the “bare foam bases” that I referred to in my post. All of these bases require a waterproofing membrane attached to their top surface along with their own drain assembly (with membrane bonding flange). I can’t imagine anyone installing the Durock base without a membrane because you could not attach your tiles to it…… it would be a total disaster. I managed to find a link to the Durock shower system installation video which shows the membrane install step: https://www.youtube.com/watch?v=G2dmFV1GfHo Good luck with your project! If you have any other questions or if you’re getting stressed about any part of the project feel free to send me another comment! Steve

• Charles · 4/6/2019

  I am a little confused about the Durock foam shower base. Do I have to put down a waterproofing membrane over the top of the foam base? Or no? It seemed at one point you said it doesn’t, and at another point you said it does. But I could be wrong about that. I’ve seen videos of both. With the membrane, and without the membrane. So I’m confused.

• Redblock · 2/17/2019

  Thanks for your comment Richard, Let me know if you have any questions for me during your project. I’m always happy to help. Steve.

• Richard · 2/16/2019

  Thank you very much for your article. After I was finished reading it, being a DIY, I knew what was the best choice for me for waterproofing my new basement shower. Other articles I had read left me quite confused. Your simple and logical terms made it easy for me to understand what had to be done and what were the alternatives. Thanks again.