Cement Backer Board for Showers – Busting the Myths

Comments (62)

• Steve · 11/26/2024

  Hi Barry, Thanks for your comment! I really prefer sheet waterproofing membranes over liquid membranes any day. My favorite one is Subliner Dry from Wedi. But you can read a lot more about my views on this topic by checking out my waterproofing membrane post. Good luck with your project! Steve

• Barry Redoute · 11/25/2024

  Hey Steve, thanks for the great info on the TBB. For a shower wall and bench, My question is what sealing method do you use (red guard, etc) on the seams and over the entire board (if any) and screws after installing the fiber cement board (like Hardie backer)? Thank you, Barry

• Steve · 6/12/2023

  Hi Tyler, Thank you so much for your comment! Although my blogging efforts can sometimes be burdensome, it’s comments like yours that really keep me going! Good luck with your project! Steve

• Tyler C. · 6/11/2023

  Thank you for all your hard work in these articles ! The shower backer board one was literally perfect, it went through every detail and facts. I’ve been reading a lot of different articles online about this subject and when I read yours I knew my answer would be here. Definitely would have paid for this information at the beginning of my journey. Thank you again for all that you’ve written in these pages !

• Steve · 1/28/2023

  Hi Denise, Thank you for your comment! You couldn’t go too far wrong installing any tile backer board, as long as it’s installed correctly. The size of the tile isn’t really important because the tile, grout and thinset mortar become a single uniform layer after curing. In essence, one super heavy tile, so the downward (shear) force applied to the backer board is the same with a 48″x48″ tile or a 6″x6″ tile (assuming the same tile thickness). I personally prefer using a cement board like Durock, or a composite board like Hardibacker, simply because these boards adds to the structural integrity and rigidity of the wall assembly. Important side note: I know it might seem like an easy DIY job because each tile covers so much wall area… much easier and much quicker, right?… Wrong! In my experience, the larger the tile, the larger the trouble. Unless the wall is PERFECTLY FLAT, the edges/corners of adjacent tiles will be very difficult to match. I’m talking about tile lippage… in a big way. I am not saying that it’s impossible to accomplish for a DIY’er, but I’m saying that you better be prepared. The correct large format tile mortar, a thick enough mortar bed, levelling clips, back buttering, a rubber hammer. Check out my Tile Installation post for more info. I’m sorry to say that I don’t think this is a DIY job. I would suggest that you hire a professional tile installer for this job. And not just any tile installer… only somebody with experience installing these large format tiles. Sorry for putting a damper on your DIY tile install plans. I just thought you should know what your getting yourselves into. Good Luck! Steve

• Denise · 1/28/2023

  Hello! Thank you for this informative post. We are considering installing large format tile in our (new construction) bathroom. The tile we’re looking at is 48″x48″ — each tile weighs 50 lbs. The shower is 60″x36″. We’re hoping to DIY the tile installation, but are a bit apprehensive about using such large tiles. Is there a particular backer board that is better suited than another, to support the size and weight of large tiles like this?

• Steve · 1/8/2023

  Hi Dave, Thank you for your comment! I appreciate that you’re trying your best to come up with a solution to this problem, but I would recommend against cutting out a strip of the backerboard. Tile backer board is a significant structural element within the tile assembly, and there’s also likely a waterproofing membrane under the tile layer. For those reasons (and others) it’s not a good idea to cut a swath out of the backer board. I’ve used two approaches to solve this problem: The first is to simply leave the existing tiles in place and apply a new strip of tiles over the existing tiles. Obviously, this technique only works if your existing tile mosaic strip is recessed enough (and your new tiles are thin enough) to allow the tile surface planes to match. It’s definitely worth spending a bit of time looking for a tile with the right thickness (uniform thickness) because of the speed and ease of this technique. There are specific thinsets (and tile surface treatments) that are engineered for bonding tile to tile. Ask you local tile wholesaler what they’d recommend. If the above is not possible, it should only take a few hours of careful work to remove this strip of tile and clean out the residual mortar. You would need to be careful not to damage the waterproofing membrane (assuming there is one). As long as you only hand tools, the backer board should be safe during this process – it doesn’t take much force to separate these tiny tiles from the mortar or to scrape away the excess mortar. I’ve used my trusty chisel to do this, but there are several tools and techniques one could use. After the section is adequately cleaned, I would apply a bonding agent like diluted Weldbond to ensure good thinset (see my Tile Installation post). I usually use Schluter Ditra (comes in two thicknesses), or stainless steel mesh, to raise mosaic tiles to match the adjacent tile plane but there are several other options. Again, you should ask you local tile wholesaler. Good luck! Steve

• Dave Palmer · 1/8/2023

  I have a decorative ring of tiles installed around my shower walls about shoulder high. It’s a row of 4 1x1in glass tiles. The person who installed them had no idea what he was doing. By the time I realized this, it was basically too late. Apparently, he had never installed the thin decorative/mosaic tiles before. Thus, the tiles are recessed. I’m tired of looking at it. I’ve contracted a company to replace the tiles, because I don’t have the experience to do it myself with any degree of certainty that it will turn out well. The person I’m working with, who has 25 years of experience installing tiles is telling me that it will nearly possible to install new tiles in the ring. The reason he says is, my has decided she wants a row of 1 inch tiles, a row of 2 inch tiles and another 1 inch tiles. The guy I’m dealing with (who will not the person to actually install the new tiles) said it will take at least 3 days, one day for each row of tiles. Not sure why that is? Anyway, I’ve done a lot of research about backer boards and your article is the most informative I’ve read. Thank you for that. So my question is this, is it possible to cut 1 inch strips of a backer board to raise the thin 1×1 tiles, install the backer board strips around the ring in the wall where the 1×1 tiles will go, and then install all the tiles at one time? The 2×2 tiles are thicker and don’t need the backer board. To me that seems like the only way to accomplish leveling the decorative tiles with the existing wall tiles. Additionally, with a backer board only 1 inch wide, what would be the best way to secure it to the wall? Do you think the backer board screw would damage the 1 inch strip? Since it’s such a small strip and probably won’t affect the underlying wall, could the strips just be installed using quick set instead? Your opinion would be great appreciated.

• Steve · 11/29/2022

  Hi Dale, Thank you for your comment! You have run into one of the most common shower remodel issues… non-plumb and non-square shower walls. I’m sure it’s as frustrating for you as it always is for me. To answer your questions: 1. I always tile the back wall (long wall) in a shower alcove first. Because this wall is the largest, it requires the most time for tile setting and it’s the most visible. As such, you don’t want to have to worry about anything other than keeping your tiles properly spaced and level during this relatively long and fiddly process. Even if the side walls of your alcove are significantly out-of-plumb, the tiles on the R & L sides of the back wall won’t likely require angle cuts (or even clean edges) because they will often be covered by the side wall tiles. I explain this in greater detail in my shower tile install post if you’d like to check it out. 2. I always prefer cementitious tile backer board to the foam stuff every time because it creates a more rigid and unified sub-structure, but there are times when I use foam board. In your situation – especially if the washer/ dryer is connected to the wall, or if the floor is not concrete, I would definitely choose cement backer or Hardibacker. This would of course involve an extra step – applying a waterproofing membrane (especially on the outside wall). See my waterproofing membrane post for my recommendations. As for the preferred type of tile for hard water, you can check out my shower tile install post for that too. Good luck with your project! Steve

• Dale Stucker · 11/27/2022

  Hello Steve, Thank you sir for covering this topic so well. Easy to read, conversational, and detailed where needed and I appreciate that. I have a couple questions. One regarding best backer board use when tiling my Delta 17″ tub/shower combo. Also a question for which tiles to set first (end walls or side wall). some background… I installed all of the plumbing for total accessibility from the ‘other side of the stub wall for future servicing should that need arise.) Currently I have my exposed studs covered at the bottom with a 6 inch tall HD self adhesive 1/16 ” rubber membrane attached to the bottom inside lip of the tub. I then covered that with HD plastic sheeting, also from the bottom of the tub lip, over the 6″ membrane, and up to the ceiling. Not pretty to look at but perfectly watertight and usable to shower with until the tile gets installed (Wife insists we don’t stop here; – ). My need to tile came to light when I tried to install the Delta 3 piece surround I purchased when I bought the tub. I discovered that the tubs 60″ side wall was not vertical and was leaning over the tub. That gap would not allow the left end surround section (with plumbing) and the right end(exterior wall) surround sections to mate up properly to the side surround section creating Big gaps at the bottom. I ruled out shimming the wall. Fortunately each wall surface is flat to itself.) 1. Would it be best to thin set the angle cut the end walls tiles first and then thin set the long side wall tiles (row by row going up) tight against the end wall tiles to help cover the angle cuts and present a smoother corner transition on the two corners surfaces? I’m planning to use 12″x24″ inch tiles set vertically. 2. On the other side of the 60″ tub side wall is my laundry room and the washer and dryer are against that same wall. Would it be prudent to use 1/2″ cement board on all three walls over using flexible Kerdi board to help stiffen the walls and help hold the cement and grout together should/When the washer decides to go dancing? Or is there a reason I’m not seeing something that would suggest otherwise? My plan is to leave the membrane and plastic in place under the backer but trim it up a tad to just above the bottom edge of the backer and tile? oh yeah. One more. Our city water here is very hard and we do not use a softener. Which kind of tile surface do you recommend for this type of water? Smooth and glossy tile or something else? Any thoughts on future cleaning of these tiled surfaces would be great.

• Steve · 11/12/2022

  Hi Edie, With a semi-rigid, solid surface material like this, I would generally say that the backer board material doesn’t matter. I don’t think you need to worry about the weight of the product. Regardless of the backer material, the silicon adhesion will significantly reduce the weight that bears down on the shower base. And if you follow the install directions, the silicon contact between the backer and the Onyx board will be extensive, so the risk of de-lamination is very low as long as you apply a bonding agent to the backer board surface before installation (to ensure good silicon adhesion). Diluted Weldbond works great for this. Good luck! Steve

• Edie · 11/12/2022

  edie 11_12_2022 I am remodeling old bathroom. I am placing onyx brand solid sheet wall panels and base. what is your recommendation on backer board. I can say 38×38 low profile base weighs 103 pounds and 38×84 inch walls are heavier yet. I would appreciate any suggestions. thanks.

• Steve · 8/4/2022

  Hi Thelo, Thank you for your comment! The first is basically an exterior stucco/ plaster finishing technique. I have seen similar methods used in showers in the (distant) past but this was decades ago. The second is an under-tile waterproofing technique engineered specifically for modern showers. It’s been lab and field tested extensively for many years, and has become “best practice” in the industry. Needless to say, I would go with the second option but with a couple of modifications. I would not apply any membrane on the studs before backer board install. Any semi-permeable membrane like “black paper” will only serve as a condensation surface. Secondly, I would not use a liquid waterproofing membrane over the tile backer board. A good “sheet” waterproofing membrane such as Kerdi DS, Wedi Subliner Dry, or Durock sheet membrane would be preferable. There is nothing basically wrong with Aquadefense but most liquid membranes do not compare with these sheet membranes in terms of their perm rating. Thirdly, I would insulate the stud cavities behind your backer board as thoroughly as possible (if it’s an outside wall). If you have a 3 1/2″ stud depth, I would seriously consider spray foam insulation in these cavities to increase R-value and decrease moisture transmission. Here’s more info from my waterproofing post. That’s my two bits! I hope it helps! Steve.

• Thelo · 8/3/2022

  Good day, I have heard from several contractors saying fluting wall is the best for the shower wall. Is that right? my understanding the way they do it using a black paper on the studs than install Steel Lath on it and start a layer of mason mortar mix wait until dries than another layer again wait until dries than thin-set mortar on top and the marble tile and grout and call it done. other said black paper on the studs 1/2 hardy backer board than coat it with (Mapelastic Aquadefense Liquid Membrane) than thin-set and marble tile and grout. two different ways and each saying this is the best way. who to believe I don’t know. your advice highly appreciated

• Steve · 6/16/2022

  Hi Angela, Thank you for your comment! It is not easy (or advisable) to remove the niche unless you are planning on removing some wall tile around the niche because the waterproofing membrane around the niche will need to be repaired when the niche is replaced. And if the tile backer board (under the wall tile) is a foam board like Kerdi Board, this will not be possible either. It is also not a good idea to attempt to remove the tile in a niche like Kerdi SN because you will essentially destroy it. Foam board and foam niches are not durable enough to be used twice. It may be possible however, to remove the foam niche and the tiles around the niche, but only if a cementitious backer board (CBU) was installed under the wall tiles. You would still need to be fairly careful removing the wall tile but CBU’s are very hard and quite durable. Sorry for the bad news. Good luck! Steve

• Angela · 6/15/2022

  Hello! I am wondering how easy it is to remove a Schluter Kerdi shower niche and replace it, or if it’s possible to replace the grouted tiles in the niche itself, along the sides and back, without damaging the integrity of the waterproofing?

• Steve · 4/15/2022

  Hi Andy, Thank you for your comment! First of all, you should not have installed your backer board before installing the pan. The installation of this pan is difficult and messy enough even when you follow their directions. As you’ve already noticed, the side walls are 1/2″ thick so only in the best case scenario will your backer board meet flush with the side walls of this pan, which is totally unrealistic. I would suggest that you install the pan flush with the back wall and one of the side walls. If the side wall you choose is not perfectly perpendicular to the back wall, you will have to make it so beforehand. After install, only the other side wall will need to be furred out to make the backer flush with the pan side wall. If this wall is perfectly parallel to the side wall of you pan, you can simply install 1/4″ Hardibacker or 1/8″ panel board (depending on the gap) to furr out the stud wall enough to allow your 1/2′ backer to be flush with the pan. More likely you will need to use a combination of shims, construction adhesive, 1/4″ hardibacker (or panel board), & your 1/2″ tile backer board, to get this wall parallel and flush. This is a very fiddly process so you’ll need to exercise some patience. Don’t worry too much if your finished wall is a bit proud or slightly recessed from the shower pan side wall. You can adjust your tile mortar thickness to accommodate. I hope that helps. Good luck with it! Steve

• Steve · 3/27/2022

  Hi Jody, Thank you for your comment! This is a marketing tactic more than anything else, since “waterproof” only means that liquid water will not flow through it – not a very impressive claim. The only measure that means anything when it comes to shower wall waterproofing membranes is “water vapor permeance”. A product’s vapor permeance rating (perm rating) represents how much water vapor will pass through it under controlled conditions. Since I can’t seem to find any reference to “perm rating” in any of the promo material or specifications, I am going to guess that its perm rating is too low to consider it a “waterproofing membrane”. My advice would be to always install a waterproofing membrane over your tile backer board, unless you’re installing a foam board product like Wedi Board or Kerdi Board. Btw, foam backer boards have a low enough perm rating to be considered true “waterproofing membranes”, that is why these products can serve as both a backer board AND a waterproofing membrane. Good luck with your project! Steve

• Jody Meyer · 3/27/2022

  I am doing research on these boards at our local Lowe’s store and found one brand (Hardieboard) with a version that says it is “100% waterproof cement board”. It claims to have “hydro defense technology” (trademarked). Do you believe that this is actually waterproof? Your article states that foam backer board is the only waterproof backer board. Any thoughts?

• Steve · 11/19/2021

  Hi Rick, Thanks for your comment! It does sound like a fun project. Firstly, I would say that if you plan to create your own mortar/cement shower pan, it’s very important to install a drain assembly that is compatible with your waterproofing membrane. This is a great video by Schluter systems that shows you how to do this with the Kerdi drain (which is a great option). As for your backer board… I wouldn’t hesitate using 1/2′ Wedi foam backer board on the walls as long as your studs are 16″ on center (or less), and you are not installing tiles smaller than 6″ (long side). Any other 1/2″ cement, fiber, or glass matt boards are also great options. For waterproofing, I always prefer a sheet membrane over a liquid. Even with your thorough insulating efforts, it would still be much safer to use a low perm sheet membrane like Wedi Subliner Dry or Kerdi DS. If you install the Wedi wall boards, you will not need any additional waterproofing on the walls but the shower floor will still require it, of course. The water resistant drywall is usually OK for the ceiling as long as it’s sealed and painted well. Wedi Board would also work great, even if you decide to tile the ceiling. It’s always a good idea to waterproof the wall-to-ceiling margin, whichever board you decide to use. Good Luck! Steve

• Rick in MI · 11/19/2021

  Steve, I am finishing a basement of a 18 year old Michigan home. The basement walls are poured cement. I used 2″ thick (R10) 4×8′ Owens Corning 250 XPS and spray foam where needed BEHIND my framing around the entire basement, along with the same 2″ XPS plus spray foam, caulk, and a thick layer of spun rock wool in the rim joints. I framed this bathroom with fir to provide additional strength and water resistance, just in case. The plan is to build the bathroom with universal design in mind to perhaps allow ageing parents to rehab there if ever necessary. Plus, my wife and I are both in our late 50s so we could perhaps use this some day also. Anyway, the sloped curb-less shower size is roughly 78×48″ with plans for a 36″ glass door opening (and a total 78″ (36″+42″) glass wall into the shower area. Three walls will be tiled, and the 48″ wall near the entry farthest from the shower heads is an outside wall. As much as I would appreciate the ease of use carrying this into the basement, I am a bit leary of using any of the soft and lightweight materials (Wedi, Schluter, etc) as a backer board, as I am concerned about possible compression from a wheelchair or walker, or falls, being a potential problem. My plan was to use some form of 1/2″ cement board and Redguard with their membrane mesh (in corners) on all three tiled walls and all 4 corners. Because I plan to build a traditional mortar/cement shower pan, I presume this needs to be coated with Redguard also. I am still trying to decide what would be best for the ceiling over the shower? The rest of the bathroom framing is covered with purple board, but the shower ceiling remains open. What backer board do you suggest that I use for the ceiling? Would 1/2″ Schluter or Wedi be rigid enough for the ceiling over the shower, or perhaps a 1/2″ fiberglass option might be better? Or maybe I should just stick with a cement board… perhaps doubling 1/4″ sheets since I will be installing these alone? This shower is not a steam shower and there will be an appx. 12″ opening above the glass wall with a heady-duty exhaust fan centered in the purple-boarded ceiling. Am I missing anything obvious/important? This is the 3rd basement and bathroom I have built, but the first one with a shower. Should be fun! THANKS in advance!

• Steve · 8/29/2021

  Hi Dan, Thank you for your comment! If I understand you correctly, your outside wall is brick (masonry) and there is no stud wall on the inside of your bathroom. If this is correct, there’s no insulation on this wall, which is a big problem. Another problem is that masonry happens to be a very effective moisture condensation surface. One of the biggest problems on any outside bathroom wall is lack of insulation. If there’s no insulation, moisture from the shower will condense on the masonry wall behind your backer board, no matter which backer board or waterproofing membrane you install, especially in the colder months. The way I would deal with this problem is to first cover the masonry wall with sheets of polystyrene foam insulation (I would suggest 1″) from floor to ceiling, sealing all the seams with polyurethane (no gaps). I would then build a stud wall in front of this foam wall and fully insulate this with regular insulation. A slightly easier but more expensive way would be to build your new stud wall against the masonry, then hire an insulation contractor to apply spray foam insulation between the studs. This method is superior because the foam effectively manages moisture penetration, as well as providing a much better R value per inch. If you do either of these options, it wouldn’t matter which backer board you choose. It’s always important to apply a good waterproofing membrane over your backer board regardless. In other words, you can repair your masonry wall for structural reasons, but it’s not a good idea to rely on this kind of treatment (Durabond) to address any of your shower waterproofing issues, in my opinion. Good Luck with your project! Steve.

• Dan · 8/29/2021

  My home was built in the early 1950s and has brick and plaster on the exterior wall. What kind of backer board should be installed over that? Some of the plaster has deteriorated and suggestions have been made to use Durabond to repair it. Is that wise? Your posts are very helpful.

• Steve · 6/28/2021

  Hi Addy, Thank you for your comment! Yes, blocking at the seams is super important with these boards so it’s great that you’ve already taken care of that. Blocking is also great to reduce stud deflection in general, so it’s a great practice no matter what board you are installing. I think a horizontal brace (blocking) at the center of each board between every stud, should do the trick (assuming you’re installing 3×5 boards horizontally) . That means that your blocking is 16″ apart vertically, which is ideal. I would also suggest that you make sure your blocking is flush with the stud face so you can screw one fastener into the center of each piece of blocking. Good luck with your project! Steve

• Addy · 6/28/2021

  Hi Steve! After a ton of research, and the desire not to handle cement backerboard since I’ll be installing my bathroom by myself, I settled on GoBoard, mostly because of availability at my local Lowes. The appeal was that it’s lightweight, and 100% waterproof. Then I came across this article, particularly about your concern for the board’s deflection. I can’t argue with that—I’ve had similar concerns. You can’t have something that light-weight and not have any compromises. I did proactively add blocking to studs where all the GoBoard seams will meet, so that will definitely address deflection issues there. I am still concerned about the center of the board, particularly between the studs, even at 16″ apart. Do you recommend additional blocking? If so, how much additional blocking per sheet? Thanks in advance!

• Steve · 6/24/2021

  Hi G, Thank you for your comment! I am not an expert on the Triton board, but it’s one of the more rigid backer boards out there so it basically gets the “thumbs-up” from me. Any rigid backer board is fine as long as you also install a good (low perm) waterproofing membrane over it. I would suggest you check out their website if you want to find out more about this particular board. Steve

• G · 6/24/2021

  This was really helpful! I’m a little confused on one point. My impression is that the Triton board is an MgO board, so although it’s cementitious, it does not contain Portland cement and has somewhat different properties.

• Steve · 6/5/2021

  Thank you Ronald. I really appreciate the positive feedback! Steve

• Steve · 4/20/2021

  Hi Ralph, Thank you for your comment! I think I’m understanding what you are saying, and it sounds pretty good to me. The GoBoard over your drywall is a fine choice, but it’s expensive. It might be easier/cheaper to use regular tile backer board (any type) and cover with a good waterproofing membrane. As well…I’m assuming that at least one of your shower walls is an outside wall, so it would be best to install a good membrane on this wall like Subliner Dry, Durock Sheet membrane or Kerdi DS. The GoBoard doesn’t have a good enough perm rating for an outside wall in my opinion. The drywall behind your backer board should be protected with either strategy. Good luck with your project! Steve

• Ralph · 4/20/2021

  Hello, The small bathroom and laundry room had to be remodeled due to water damage in my doublewide. (Stupid Hot Water Heater). The bathroom had 3/8″ Vinyl on Gypsum Sheetrock Walls. And my Bathtub/Shower Walls were just a thin plastic that was held up to the Vinyl on Gypsum with Adhesive and Plastic Rivets. I was suprised to see that the thin plastic shower walls never leaked through to the Sheetrock. I couldn’t get Vinyl on Gypsum Sheetrock to Replace. I just used Regular 3/8″ Sheetrock and painted 2 coats of primer and 2 coats of paint. My plastic 60″ x 30″ bathtub fits inside the Sheetrock Walls. Meaning the tub flange is exposed and not hidden or tucked under the Sheetrock. Meaning the tub flange doesn’t sit right up against the studs. The Sheetrock is between the Studs and tub flange. I want to screw 1/4″ GoBoard 3′ x 5′ over the Sheetrock to the studs so that I will be out past the tub flange. Then seal the seams per manufacturers instructions. Wait 24 to 48 hours for sealant to completely set up. Then install DumaWall Vinyl Waterproof Wall Tiles with Loctite Power Grab Construction Adhesive and Seal each seam in the DumaWall Tiles with a 100% Silicone has I install the DumaWall Tiles which is Manufacturers Instructions on a Completely 100% Waterproof Seal. My Studs behind the Sheetrock are 16″ on Center. But my thinking is that not tearing out the Sheetrock will help keep the Foam Board more structurally sound. Do you think this will be a good structurally sound, waterproof/water tight seal that won’t leak back to my Sheetrock Walls or Studs? Also is the Foam Board overkill or could I get away with just using one of the other backer board types? I was thinking GoBoard because it’s just easier for one person to install and it’s not a big mess to waterproof it. Just seal the seams and that’s it. Problem is, it’s not that easy to get the GoBoard at my local hardware store. Thanks, Ralph

• Steve · 3/29/2021

  Hello Jerry, You can install the Kerdi shower pan with Mapei thinset as long as its unmodified. Mapei has a few unmodified mortars including “Kerabond” and their “Floor Tile Mortar”. I would always use a sheet membrane over a liquid membrane every time. The regular Schluter Kerdi membrane is fine to use on an interior wall but I would install the Kerdi DS membrane on the outside wall if I was you, especially if it’s a 2×4 wall. Kerdi DS has a much better perm rating. Good luck with you shower project! Steve

• Jerry · 3/26/2021

  Hello Steve: Thanks for information. it is very useful for me. I am planing my bathroom now. i will use kerdi-shower tray,Durock cement board,Kerdi waterproofingembrace(one exterior wall,one inside wall).My question is should use Schlutet thin-set mortar laydown tray to the subfloor? can i use Mapei mortar?i already have.and about membrace use it too. Another question is red gard and Kerdi membrace which way is better? thanke

• Redblock · 3/3/2021

  Hi Morley, Thank you for your comment! I fully endorse your decision to use plywood as your first stud wall covering. I have often attached plywood to the stud face to create extra rigidity. I’ve also evened out a non-planar stud wall by attaching ply to a selectively shimmed stud wall to create a perfectly planar surface prior to backer board attachment. This helps reduce tile lippage. I also think it’s perfectly OK to install the Kerdi board over the plywood. You can see in this Schluter video that they are actually OK with attaching Kerdi board over existing drywall so it would be unreasonable for them to suggest that you can’t install it over plywood. Plywood is one of the most awesome building materials ever invented so I would never discourage its use to stiffen up a wall that will have unusual stresses applied to it (like a wall hung toilet). Most wall hung toilets do not technically require this, but I certainly don’t think it’s overkill. In other words… go for it! Good luck with the project! Steve

• Morley Walbaum · 3/3/2021

  Hello Steve Are there any issues with installing Kerdi Board over 3/4″ plywood sheathed stud wall in a shower. I am completely renovating a 6’0″x 10′-0″ bathroom which will have a 3′-0″ x 6′-0″ walk in curbless shower at one end. I would like to install 3/4″ plywood over the 2 x 4 studs (16″ oc) on the 10′-0″ plumbing wall which also includes one of the end shower walls. This is desired for a couple of reasons: 1) mostly for backing for a wall hung toilet (Geberit carrier) & less critical for a wall hung vanity & LED mirror 2) the plywood thickness will also reduce the the length of the 6′-0″ by 3/4″ which is reqd to fit the tile module 3) the plywood at the end of the shower will allow for various locns of the sliding handheld shower head track. Within the shower I will attach 1/2″ Kerdi Board over the plywood but only attach thru the plywood where the studs are located. I will be installing 6″ x 18″ Carrera marble over the Kerdi Board within the shower. I have emailed Schluter but there only comment was to install over open studs not over plywood, – no other explanation even though I have sent further emails requesting Schluter’s reasoning? Not sure why the plywood would not be allowed under Kerdi Board that is only attached at stud locations. Is it that unstable of a material even though its behind a waterproofing membrane on an interior wall? I have purchased all of the materials a while back or I would switch to another product line. Can you shed any light on this? Further: Is it worthwhile to use plywood over a wall hung toilet carrier or is this overkill?

• Redblock · 3/1/2021

  Hi John, Thank you for your comment! I would always suggest using a good tile backer board for any shower wall. Either cementitious or Wedi foam board. If you use regular TBB, I would always suggest a good sheet waterproofing membrane be used as well. This is especially important on any outside walls, even if you decide to install foam board. If you are asking about the finished wall surface, I would always suggest a porcelain tile. Much lower vapor transmission through these compared to ceramic tile. Also a good water resistant grout like Mapei Flexcolor CQ. A curbless shower is always a challenging project for any DIY’er but I would always recommend it because it’s a very satisfying project, and a super cool look! However, you should never do this project without following the rule book (manufacturers install instructions, in other words). There is no room for error with a curbless shower. If you are leaning towards a foam shower pan, I would suggest a Wedi pan. The cement and fiberglass mesh coating makes it so much more resistant to damage during install and during its service life. Good luck! Steve

• John mack · 2/28/2021

  Hi Steve , you have packed a ton of info right there!! I wish you were located in Mytown Canada. We are planning a remake of a small bathroom, maybe with curbless entry, maybe not. A Kerri product appears likely. We are considering a Tile redi pan. One end wall is exterior. At 35 years old construction, we had drywall fail at around year 5-8. For a finished surface on the shower/tub wall, we used vinyl flooring, and it works well! Tons of patterns and colors. My wife painted it, and it still looks like a new install, to me. What products, material would you use for the interior exterior wall rebuilds, and is curbless somewhat ok ? John m . Thankyou for your hard work here! Thank you.

• Redblock · 2/23/2021

  Hi Richard, The GoBoard install instructions suggest that you can use both unmodified and modified mortar to bond tiles to its surface so presumably they are suggesting that both will stick well to the bare board as well as the sealant covered sections. Personally I would only use a modified thinset mortar because it should adhere better to the sealant covered areas than unmodified. I don’t really have a favorite modified mortar. You just have to make sure the one you choose is rated ANSI A118.4 (most are). That’s what Johns Manville recommends. Good luck with your project! Steve

• Richard Goldman · 2/23/2021

  In your opinion, which mortar has the best adhesion to cured GoBoard Pro Sealant? The product is very sticky when applied, and seals seams and screwheads beautifully. It’s totally waterproof, which is a huge positive. However, I’m a little concerned in areas around windows and doors, where much of the GoBoard is covered in cured sealant, that the tile mortar may not bond well to it. Should I be concerned, and, if so, can anything be done to enhance the adhesion of the cured GoBoard Pro Sealant?

• Redblock · 2/21/2021

  Hello again Gene, If I am understanding you correctly, you tub will be on a framed “box” that sits on the concrete subfloor. If so, It must be super strong to take the weight of a cast iron tub filled with water. I would go big on the support. I am not sure what you meant by “framed 26 centers” but if that means 26″ on center, that is not nearly enough. Make it strong…at least under the tub legs. 8″-12″ on center with a 3/4″ plywood deck would be great. Permabase screwed over top with a thinset base would be great as well (apply with 1/4″ square notch trowel). The Permabase would be a much better substrate for tile bonding and it would add rigidity. Claw foot tubs legs deserve extra support because the weight is bearing down on only four small points. And it also wouldn’t hurt to install a waterproofing on this box to keep any standing water from penetrating. Good Luck! Steve

• Gene Eckhoff · 2/19/2021

  Hi Steve, thanks so much for your quick response! I have one other question for you on the same project. The cast iron tub will be on a raised 2×6 platform framed 26 centers to accommodate a trap and drain as this is located in a basement over radiant slab. It has a 3/4” subfloor and I will add 1/2” backer (permabase). I’m thinking it would be more rigid to bond the backer to plywood with thin set and screw. Would you recommend that and if so what size notch trowel? BTW, I decided to go with waterproofing for the peace of mind. Thanks, Gene

• Redblock · 2/18/2021

  Hi Gene, Thank you for your comment! I agree with you. You should not need a waterproofing membrane on that wall if it’s an inside wall, and it’s not going to be exposed to any water. If there is any possibility of splashing against this wall, it would be a different story. Either way, you should consider using a water resistant grout like Mapei Flexcolor CQ. Good luck with your project! Steve

• Gene Eckhoff · 2/18/2021

  Hi Steve, Thank you for your very informative post. I will be installing a tiled wainscoting about 4′ high in an alcove on an interior wall that abuts the furnace room. And was planning on using Durock or permasheild as backer, the tub in this case will be a free standing cast iron clawfoot that will have a curtain track on the ceiling when using shower. Would you still apply a waterproof membrane in this case or would mesh tape and thinset be adequate over seams and fasteners? I understand why it would be necessary in a tub surround or fully tiled shower, but it seems very unlikely that the tile would ever see much exposure to water. thanks so much for sharing your expertise! Gene

• Redblock · 1/28/2021

  Hi Neil, Thank you for your comment! I’m happy that my post has been useful to you. In my opinion, foam boards are generally adequate for inside walls, but I always prefer to install a standard cementitious backer board and a good sheet membrane like Wedi Subliner Dry for any outside walls. The Wedi sheet membrane has a .05 perm rating compared to the foam boards by Schluter and Wedi which are around .5 perms. That means these foam boards are 10 times more permeable to moisture! For the reasons mentioned in my post, I believe it’s very important to limit moisture transmission into outside walls as much as possible to avoid condensation in the stud wall. I am also not crazy about the flexibility of foam boards when installed on a wall with 16″ stud width, unless bracing is installed in the wall and you’re installing a cement faced board like the Wedi foam board. Good luck with your project! Steve

• Neill · 1/28/2021

  Hi Steve, really excellent post, many thanks for taking the time to share your expertise. I’m having my shower re done. Having taken tiles off I’ve noticed the previous installer did absolutely no waterproofing at all, just normal plasterboard. And can see all of the issues that you describe first hand. I’m ripping off the boards and taking it back to studs on one wall, and building a new frame on the other. I’m undecided as to whether to use the foam based tile board or the cement type like hardibacker. I think the foam sounds better in terms of its waterproof nature, but I am concerned over the strength of the wall if these are used. Could I ask, if this were your project in your own house, what board onto the studs would you choose to use?

• Redblock · 1/17/2021

  Hi Alysha, Wow! I’m super happy that you got some valuable info from my post. It’s very validating and motivating for me as a relatively new “blogger”. Good luck with your project! Steve

• Alysha · 1/16/2021

  I just wanted to give a big Thank You for such a detailed and informative post. Me and hubby are getting ready to reno our 1950’s pepto-bismol, original-plastic-pearlescent-tile bathroom. There is no fan in this room and everything is approx 70 years old. The tiles are falling off the walls, and I’ve finally had enough. I fear the amount of mold hiding behind the walls, so we are planning on taking her down to the studs and only keeping the bathtub. This is our first big solo renovation. While my parents are SUPER DIY and have been very helpful with other (weekend) reno’s, they live 3 hours away. This is not a weekend-only project, so we’re prepping to do most of it solo (with a 2 yr old underfoot, to boot). This post was super informative and helped me understand the differences in backer boards, and which would be best for my situation (durock). One step, out of about 1 billion that I can check off as “I’m pretty sure I understand/made the right choice”. THANK YOU!

• Redblock · 1/16/2021

  Hi Bob, Thank you for your comment! If you’re simply furring out the wall and installing foam backer board over top, you really don’t need to install tile backer board. Plywood would be cheaper. Good luck with your project! Steve

• Bob Marquid · 1/15/2021

  Hello Steve, I really appreciate your insight, thank you. My house is a post and beam constructed from an old barn. Our main bathroom shower is a tub surrounded on three sides by walls covered with tongue and grove pine boards. the tub is surrounded by shower curtains hanging from an oval rod suspended above the tub. I’m planning to tile down to the tub on three sides and enclose the front with a glass door. The walls are mostly plumb however, there is a beam that runs inside the wall horizontally about 4 feet above the tub and sticks out about 1/4″ past the surface of the tongue and grove pine on the wall. I’ll need to shim the wall out to make it plumb. Would you recommend that I use a cement board as a sheeting and then apply my foam backer board on top of that?

• Redblock · 1/6/2021

  Hi DS, Thank you for your comment! You should probably ask this question to your local building inspector but it’s a pretty safe bet that you need to install a fire rated backer board. Since you are removing the original wall material, you would likely be required to meet the current code standards. I would suggest you install a cement board like Durock cement board because it apparently has a 2 hour fire rating. Kerdiboard does not seem to have any fire rating at all. And if Durock is not available in your area, it’s pretty easy to look up fire ratings for any other brand of cement board online. Good luck! Steve

• D Smith · 1/5/2021

  Hi Steve, My tiler is replacing our tub surround in a 1970 condo. One side adjoins the building electrical room and another side adjoins our neighbour’s wall. There is 1/2″ gypsum on the opposite side of our studs, then more studs on the other side of that, before the neighbouring walls. The tiler has brought 1/2″ kerdi board to put directly on the studs, and thinset then porcelain 8×12 tiles are supposed to go on top. I am mainly concerned about meeting fire rating which I believe is one hour. Any advice? Thanks, DS

• Redblock · 1/5/2021

  Hi Michael, Thank you for your comment! I will be writing a shower base post that will include info about shower wall drains, but for now I’ll address your questions directly. The installation of wall drains like this one are quite involved, so you should make absolutely sure that the contractor you hire is experienced in their installation. Personally, I’m not really comfortable with the requirement to cut a big notch out of the bottom plate of your shower wall (see install instructions for WALLD48). This plate is important to prevent flex in this wall. I would never cut a notch out of it for any reason. If you cannot fur out the wall enough to allow the drain hole cutout to clear the bottom stud plate, I would not install it. I would also recommend that you not install this wall drain on an outside wall unless the wall is furred out significantly (as mentioned above) to allow for adequate insulation in the wall adjacent to the drain pipe. Good Luck with your project! Steve

• Michael · 1/5/2021

  Hi Steve, Can you talk about installing a shower wall drain? The drain we’re going to use in our master bath remodel is the Wall 48 from QuickDrain. Any installation issues I should be concerned with? My primary concern is how reliable it is. Is this particular drain style difficult to install? What, if any, are the risks/negatives of using a wall drain? This drain installation needs to be bulletproof in terms of NOT LEAKING! Can you advise me on how to make sure the contractor we choose does a great job?! Would you be comfortable using an experienced contractor that has never installed a wall drain? Thank you!!

• Redblock · 12/16/2020

  Hi Brian, If you are installing a mud pan with a waterproofing system like Redgard you don’t need to worry about water wicking up from the pan into the walls and curb because you are applying your waterproofing membrane over the base and backer board. Any undertile waterproofing membrane like Redgard will essentially prevent moisture from getting into this margin between the pan and walls. I would recommend fiber taping the joint between the floor and walls and apply three coats of Redgard. If you do this, you can install the backer board before you install the pan or afterwards. It won’t cause any problems either way. If you install the backerboard after, you should place the board directly on the mud pan. You do not want any gap between them. Here is a fairly good video showing a mud pan installed with a Schluter Kerdi waterproofing membrane. Good luck with your project! Steve

• brian · 12/14/2020

  i read if you install hardibacker or some other cementious backerboard then build the mud pan burying the backer board. water will wick up from the shower pan into the walls & curb and start destroying the backer board. if i built the shower pan then installed the backerboard leaving about 1/4″ gap between the mud floor and walls. of course i would red gard everything. is this a good practice or should i put the backerboard onto the mud floor.

• Redblock · 11/10/2020

  Hi Ivy, Thank you for your comment, and your compliment! It’s always best to do as much research as you can about products and “best practices” before you hire a contractor, and ask as many questions as you need to feel comfortable with the work they’ll be performing. Any decent contractor will welcome this kind of discourse because they’re proud of their work, and they’ll be happy that a client can appreciate all the work that nobody sees as well as the finished product. Ask your questions……and if they get uptight or defensive, move onto the next one. One of my past clients asked me when we first met “Are you going to install the orange stuff in my shower”. And the answer was yes! (she was referring to Schluter Kerdi waterproofing membrane). She was certainly no expert in the details of shower waterproofing but because of her research, she was able to indicate to me that it was important to her. Of course you will not turn a bad contractor into a good one by asking these kinds of questions, but it will indicate that you’re concerned about the “behind the walls” details and you’ve done your research. I think it makes a big difference. And if you think anything is going sideways during the project, you can always ask me! Good Luck! Steve

• Ivy Hernandez · 11/9/2020

  I love your posts – thank you so much! I’m going to hire a contractor to do bathrooms and kitchen. How can I assess whether he’ll use all the best practices you suggest? Like plombing and waterproofing the niche? Just ask?

• Redblock · 9/2/2020

  Hello again Emir, Yes, it’s always important to install a waterproofing membrane. I have not used the Durock sheet or liquid membranes but both seem like fine options for inside shower walls as long as the install directions are followed. Good Luck. Steve.

• Emir Demirovic · 9/1/2020

  Steve, thanks for the response. None of the shower walls are outside. Do I still need a waterproofing membrane over Durock cement board? Is the membrane made by Durock good option?

• Redblock · 9/1/2020

  Hi Emir, Thank you for your comment! I prefer Wedi Subliner Dry or Kerdi DS sheet membranes. These two (and a few others) have very low permeability so they are important to use if one of your shower walls happens to be an outside wall. I would suggest that you check out my waterproofing membrane post if you want more info. Good luck with your project! Steve

• Emir Demirovic · 9/1/2020

  My installer will be using Durock cement board on the walls. What type of waterproofing membrane do you recommend over the Durock board. Thanks Emir

• Redblock · 5/22/2020

  Hi Roderick, Thank you for your comment. Although I haven’t installed Wonderboard Lite, I believe that it’s a decent tile backer board. However, your contractor should have installed a waterproofing membrane. I would never build a shower surround without applying a sheet or liquid waterproofing membrane to the tile backer board surface. There is an extremely high chance that moisture will condense in the shower wall if there is no membrane, especially if it’s an outside wall. If your contractor built a custom niche, the niche box should have a 2×4 frame around its perimeter with plywood backing. Then the Wonderboard should be attached to all the interior surfaces and a waterproofing membrane applied. An even easier strategy would have been to build the 2×4 niche frame only, then attach a premade (prefabricated) foam shower niche to this framing (no plywood backing needed). These foam niches come in various sizes so there is really no need to build a custom sized niche unless you insist on unconventional sizing. Sorry for the bad news. I know that it’ll be uncomfortable talking to your contractor about this so I wish you good luck! Steve

• Roderick James · 5/22/2020

  I have a contractor and he used Wonderlite backer board. He did not put any liquid membrane on it or anything. He just put the tile on top of that. Is that safe? He also built a niche, but behind the niche is just drywall, not the Wonderlite backer board…he cut through that to build the niche. Is that appropriate?