Shower Membrane Waterproofing – The Definitive Guide for DIY’ers & Pros
The MOST IMPORTANT step in any shower remodel is waterproofing with a shower membrane.
In this post I, Steve of SKG Renovations (Steve’s Bio), will be using my extensive knowledge and experience in bathroom and shower remodelling to give you the whole story about shower membrane waterproofing.
I will explain the different types of shower waterproofing methods available, which ones I prefer and why.
Brief History of Shower Waterproofing
You might be wondering, “Is shower membrane waterproofing a new thing?” and “Why did the industry decide to abandon the old-school strategies?”.
Well those are good questions. And the answers to those questions provides a good background for this post about waterproofing products and strategies.
Shower waterproofing is not really a new thing. In the past (15+ years ago) it was assumed that the shower surround was relatively impermeable to water, and the shower base was the only place where any waterproofing was installed.
Older homes also were a lot more forgiving when it came to water penetration in and around the shower assembly.
Older homes were quite drafty with significant air leakage between the inside and exterior of home. Moisture that leaked out of the shower stall could often evaporate under these conditions.
This resulted in a far less comfortable home that was expensive to heat, but it also lessened the danger of mold growth, dry rot, and toxic air being trapped in your home.
Although adequate air movement helped a little, ultimately the problems could never be ignored because of the mistaken assumption that the tiled walls in a shower are essentially waterproof.
This was the flaw that ultimately caused all showers built in that era to fail regardless of the quality of the installation. Ceramic tile usually failed faster than porcelain because of higher absorption rates through the tile, but they all eventually failed.
Old School Shower Pan Liner
Because the shower floor is a horizontal surface always immersed in water, it is a very intuitive place to install some measures to prevent water from getting underneath and rotting your floor framing.
In the past, these measures usually involved the installation of a rubber or copper shower pan liner (or membrane) below a traditional mortar base to protect the subfloor beneath. This was considered a water in / water out system.
And this method is still used today by installers that subscribe to the “if it ain’t broke, no need to fix it” school of thought.
If installed correctly, this membrane did exactly what it was supposed to do; keep water from getting into the subfloor and wall base framing.
The only problem was that this method assumes that water penetration through and around the mortar base was acceptable as long as it eventually made its way towards the weep holes at the base of the drain. And I can tell you from personal experience that this assumption was not at all acceptable.
Since tile, grout and mortar was never designed to be waterproof, a significant amount of moisture always made it into and around the mortar base, pooling at the liner.
Even with the proper pre-slope below the liner, much of the water adhered to the porous mortar base so it always stayed significantly hydrated.
When this happens, the mortar base breaks down and mold starts to grow. I have seen this in countless demolitions, even if the subfloor had the proper slope and the weep holes were not blocked.
The result was always a rank, toxic smell from the bi-products of rubber and cement breaking down, and mold….. lots of mold. A seriously flawed design in my opinion.
In other words, It was a bad idea before, and it’s still a bad idea today.
Shower Wall Waterproofing
Before the waterproofing membrane systems were developed, there wasn’t really any consistently applied waterproofing strategies for the shower walls except for the shower pan liner which usually ran up the wall only about 1′ above the shower base.
Most building codes also required that a vapour retarder membrane (plastic sheet or building felt) be installed between the studs and the backer board on outside facing walls, to limit moisture transfer into the framing.
This code rule is still in place today in most parts of the world but it has always had serious limitations such as inconsistent coverage and varying degrees of moisture permeability.
The new problem is that this old system is incompatible with new shower waterproofing membrane systems and can cause major problems with condensation in your outside shower wall.
These old shower wall waterproofing methods were seriously flawed and needed to be replaced with the new membrane systems, not supplemented by them.
Shower nooks and niches – Most problematic
It is easy to see how shower nooks and niches could be the cause of major water infiltration issues in the showers of the past, when they still cause problems in some shower today.
A hole in the shower wall was always a risky undertaking and almost always resulted in water running into the shower wall no matter how careful the contractor was when building these problematic shower boxes.
There were no preformed ready to install tileable foam shower niches back then, and no shower waterproofing membranes, let alone quick to install finished shower niches. All these wall nooks, niches and soap trays had to be custom built by the framer or tiling contractor.
They had to use the materials available at the time, so wood studs framed it, tar paper “waterproofed” it, gypsum wall board lined it, and tiles were laid over it. At the time, tile and grout were considered to be relatively impermeable to water so it was not considered to be a problem.
This was a grossly mistaken assumption, but fairly common during that period. Needless to say, it didn’t take long for these assemblies to rot, causing the tiles to break off and water to get into the wall framing.
Fixing the Leaking Shower
The new shower waterproofing membrane technology has basically solved all of the problems of the past by placing the waterproofing layer directly beneath the tile layer and combining it with decoupling.
These technologies have truly revolutionized the entire tiling industry, including the way that tiled showers are constructed and waterproofed.
There are basically four main types of shower wall and floor membranes:
Sheet and liquid membranes, as well as the newer foam wall boards, foam shower bases and foam shower niches (in the foam wall boards category).
Each of these products have some similarities and some important variations that I will go over in detail.
Sheet membranes are also different from liquid waterproofing membranes in that they can also serve as uncoupling membranes. Before we get into the details of each type of waterproofing membrane, I will try to explain what uncoupling is all about.
Decoupling / Uncoupling Membrane Mystery
One of the additional benefits of the sheet style waterproofing shower membranes is that they can also serve as uncoupling membranes.
Not many people understand the term, or the purpose of uncoupling the tile assembly from the backer board and I can’t really blame them. There are some complex physics involved in these systems and frankly most tiling professionals don’t really have a clue either.
I will attempt to explain the basics of uncoupling in the following sections.
Crack Isolation Membranes
The explanation of crack isolation membranes goes a long way to also explain the advantage of the uncoupling membrane in the shower:
Most of you have probably seen tiled floors that have cracked along their grout lines, sometimes quite dramatically. This is often the result of a crack in the concrete floor beneath the tile.
When the tile is firmly attached to a concrete subfloor, the crack that forms in the subfloor will crack the tile assembly attached to it as well, usually separating along the grout lines. This horizontal movement can also cause tile delamination around the crack.
A crack isolation membrane is basically just a thicker and heftier version of a waterproofing membrane that can stretch horizontally sometimes as much as 1/8″.
This type of membrane can reduce the chance of grout line cracking in the example above, by floating the tile assembly (tile, grout, mortar) on the surface of the membrane so it can stretch horizontally as the floor cracks, instead of the tile assembly being pulled apart (explained more thoroughly in the next section).
Uncoupling Membranes in the Shower
Because the shower floor and shower walls are exposed to lots of moisture and wide temperature changes, this is also a place where grout line cracking can occur.
This can happen in the same way as the floor example above but to a much lesser degree. Without a uncoupling membrane, the bottom backer board layer can expand and contract at a different rate than the top tile layer, causing grout line cracking.
This movement can occur at the margins between two adjoining backer board panels, or most often in the corners where the wall meets the floor, and where the back wall meets the side walls.
Uncoupling can solve this problem by essentially disconnecting the top tile layer from the bottom backer board layer.
Uncoupling is accomplished by the mortar attaching not to the membrane sheet itself, but only to the fleece fibers (tiny plastic hairs) on each side of the sheet. This creates a tiny gap at the base of the fleece on each side of the membrane sheet.
This tiny gap allows the assembly on top side of the membrane to move a little. Not much, but it’s enough to allow the tile, grout and mortar to essentially float over the backer board while still able to carry a significant load.
Genius, right? Like I said, I wish I would have invented it!
Types of Waterproofing Membranes
Sheet Waterproofing Membranes
The sheet membrane is exemplified by the brand leader in the industry, Schluter Systems and their Kerdi waterproofing membrane, but there are several other brands as well (more on brands later).
These sheet membranes are made from a blend of plastic compounds designed to be attached on the surface of the tile backer board and shower base with either a thin layer of tile mortar, or “peel and stick”.
The peel and stick shower membrane only requires a primer to be applied before sticking it to the backer board or shower pan. These are not too common in the US but more common internationally.
To seal the corners of the shower surround, these membrane systems use preformed / molded membrane pieces sold separately. You mortar or stick these pieces in place similar to the membrane application.
Your wall tile and shower floor tile is then attached to the membrane with a layer of thin-set mortar in the same way you would set any tile, using the appropriate sized notched trowel for your tile.
Both front and back surfaces of the membrane are specifically designed to bond to most thin-set tile mortars.
Liquid Waterproofing Membrane
The liquid waterproofing membrane is exemplified by the most popular of these products, Redgard Waterproofing Membrane by Custom Building Products, although there are also a number of other brands out there (more on that later).
This type of product can be considered a waterproof paint for your shower because the most common method of application is with a paint roller. You can also spray it on with a paint sprayer.
After it dries it turns into an elastomeric (rubber like) layer which stays flexible.
This is the cheapest and easiest way to waterproof your shower walls and shower floor and it does provide good protection in most cases if applied correctly.
It can also be the fastest way to get the waterproofing job over with asap, if you pick the right product and the weather is not too cold or wet.
Some of liquid membrane manufacturers claim that they can also serve as a crack isolation membrane if they are applied a little thicker.
Foam Tile Backer Boards
I included these foam backer board products in my shower membrane post because they are the only waterproof wall boards that are designed to serve as tile backer boards.
Just like ordinary tile backer boards, they can serve as a structural, dimensionally stable and load bearing substrate for tile as well as a waterproofing shower membrane.
The wall boards are made from extruded polystyrene foam and have a layer of material on both sides designed for tile mortar bonding.
This bonding layer is most often a plastic fabric with fleece webbing for bonding and decoupling however, there are a couple of products that have a cementitious material bonded to their outer surface.
They are attached to the wall with specially designed fasteners, with washers to prevent the screw head from pulling through the material. The fasteners are later covered with adhesive or a small piece of membrane to maintain membrane integrity.
The wall boards come in various thicknesses to allow you to use them as building panels as well as backer boards. Most manufacturers are encouraging their use for quick and easy shower bench construction as well as waterproof partition walls, tub decks, etc.
Foam Shower Bases
Foam shower bases (or shower pans) are sold separately or as part of a shower kit that contains several shower waterproofing components.
These components often include a foam shower curb that is secured and waterproofed in the same way as the base. They also include other essential components like a membrane bonding shower drain and corner and seam tape to reinforce and waterproof the perimeter and seams.
The shower bases are formed from the same foam material as the wall boards, some having a mortar bonding layer on their surface and some not (more on the this in the Foam Shower Wall Panels, Bases & Shower Niches section below).
There are some standard size shower base and shower pan kits with either right hand, middle, or left hand drain orientations. And because they are made from foam, they can easily be trimmed to match your shower size and drain position by using a circular saw, hand saw or even a utility knife.
There is no need to pre-slope the subfloor or install a rubber or metal shower pan liner to the subfloor with this system. The foam shower base simply bonds to the unaltered subfloor with thin-set tiling mortar.
Most, but not all of these shower bases require a membrane to be applied over their entire surface. This type includes a drain assembly with a membrane bonding flange that is attached to the polystyrene with thinset mortar.
The bases that are covered with a cementitious coating do not require a membrane to be bonded to their surface and include a drain assembly that glues into place with a special adhesive.
All of these foam shower bases also require their entire perimeter and seams to be sealed with either preformed membrane corner pieces attached with thinset mortar, or strips of fiberglass tape applied to all the corners and seams, then covered with a thick waterproof adhesive.
The New Age of Shower Waterproofing Products
I have gone over the various types of shower waterproofing membranes above. Now it’s time to give you a rundown of the brands within these categories.
I’ll try to go over their distinguishing features as well as my preferred products and install techniques.
But first, a little background about how these membranes are rated for moisture permeability.
Striving for the Perfect Shower Seal
I should make it clear that there is no such thing as perfect shower seal or perfect waterproofing for your shower.
The term “waterproofing membrane” is in fact misleading; No membrane is completely waterproof. They all belong to larger classification of Vapor Retarders. Any vapor retarder will only limit the amount of moisture that can pass through it, not eliminate it.
Vapor retarders are rated as to their moisture permeability and given a “perm rating” that represents how much water vapour will pass through the material in a given period of time at a given pressure (1 grain of water vapor per hour, per square foot, per inch of mercury).
There are three vapor retarder classes that all waterproofing material’s fall into.
Class I: 0.1 perm or less (these are generally considered vapor barriers).
Class II: 0.1 – 1.0 perm
Class III: 1.0 – 10 perms
Most shower waterproofing membranes fall into Class II but some end up in Class III as well. The bottom line is, the lower the perm rating, the less moisture will get through the membrane.
There are not a lot of established requirements when it comes to the definition of a waterproofing membrane for use in a shower environment. The only rules that have been established are related specifically to steam showers. If you are interested in the specifics of the testing procedure, it can be purchased from ASTM International: Procedure E of ASTM E96.
I will explain the significance of perm ratings for different shower installations a little later when I give you my opinion and recommendations.
Sheet Waterproofing Membrane Products
I will be listing a few of my favorite sheet membrane products in order of their perm rating, starting from the lowest (least permeable) to the highest.
This sheet membrane system was engineered for the high water vapor environment of steam shower. The difference is that this membrane has a exceptionally low .05 perm rating according to the manufacturer.
As far as I know, Wedi Subliner Dry has the lowest perm rating of all the shower waterproofing membranes in the industry.
It is also engineered so it can be used on both shower walls and shower bases.
In addition to their sheet membrane, Wedi also has a range of polystyrene foam products that make up an entire wet room system. This includes shower bases, shower niches and building panels.
Durock sheet waterproofing membrane have a .079 perm rating so it is also very good compared with the other sheet membranes. It’s also engineered for shower walls and floors.
Like the others, Durock also makes a line of polystyrene shower products, including shower bases, curbs, benches, ramps, tile backer board , building panels but no foam shower niches. They do however make a waterproof ABS plastic shower niche that has a fleece surface for tile mortar bonding.
None of their polystyrene products have any coatings on their surface to facilitate the bonding of tile mortar.
Noble has a couple of good sheet membrane products designed for shower waterproofing. Their Wall Seal is the cheaper of the two with a perm rating of .44 but it is not rated for the shower floor.
For shower floors you will have to get NobleSeal TS which is their best waterproofing membrane for showers.
This material is rated for steam showers with a very low rating of .15 perms. This makes it one of the better shower waterproofing membranes in the industry. Engineered for both shower walls and bases.
The Kerdi waterproofing membrane is by far the most popular sheet membrane at the moment.
Schluter originally claimed that only unmodified mortar can be used to attach their membrane because it’s composed of lime based cement, which can easily cure under a vapour retarder like kerdi. Modified mortars apparently can take too long to cure, compromising their bond strength.
That said, Schluter now makes it’s own modified thin set mortars that apparently can be used above and below their Kerdi and Ditra membranes. It’s magic, I guess.
According to Schluter, if you follow the application instructions you should be able to tile over Kerdi immediately after it’s installed, which is common for most sheet membranes.
The standard Kerdi membrane has a perm rating of .75 but Kerdi DS has a .19 perm rating. Kerdi DS was engineered for the harsh environments of steam showers.
Paint On Liquid Waterproofing Membranes
As I have already mentioned, Redgard is the most popular and the most talked about liquid waterproofing membrane out there.
All liquid waterproofing membranes are applied either with a brush and roller that would be used for painting, or sprayed on with a paint sprayer. Most professionals and DIY’ers use a roller and brush.
The use of a wet film thickness gauge (supplied) is recommended with all liquid membranes as well. This ensures that it is applied to the correct thickness. If it is not, it will compromise its waterproofing qualities (and its warrantee).
Joints or changes in plane (wall to floor) can be reinforced with fiberglass mesh tape and recoated with Redgard if you want “extra protection”, but this is not a requirement according to the application instructions.
This type of membrane requires at least 2 applications for it to have the proper thickness for shower waterproofing. In warm dry weather it can dry very quickly but may take up to several hours between coats and again before tile can be applied over it.
You must allow 12 hours to cure before flood testing.
Redgard has a perm rating of .36 when applied according to the application instructions.
This liquid membrane is also quite popular and effective if applied according to the instructions. It basically has the same application procedures and limitations as the other liquid membranes.
The manufacturer says that a reinforcing tape in the corners and seams is optional but they also sell this type of product (Mapeband) if you want to “provide additional protection”.
It can also be used as a crack isolation membrane up to 1/8″ according to the specs.
Aquadefense has a perm rating of <.5 according to the manufacturer which is intentional because they engineered it to meet the requirements for steam shower waterproofing membranes (Procedure E of ASTM E96).
Hydro Ban is also one of the more popular liquid membranes out there.
It has a significantly higher perm rating at 1.25 perms so it is not rated for steam showers.
It can also be used as a crack isolation membrane and it does not require any reinforcing mesh be applied at the seams or corners according to the application instructions.
Foam Shower Wall Panels, Bases & Shower Niches
There are a fair number of companies producing and selling foam wall panels, shower bases and preformed shower niches today and more are jumping on the bandwagon every other month it seems.
These products are getting extremely popular because they can help you build and waterproof your shower far quicker and easier than ever before.
Here are a few of them.
As I already mentioned, Kerdi Board is the most popular of the foam wall boards out there. They also make the most popular foam shower base available.
Their wall boards come in 1/2″, 5/8″, 3/4″ and 2″ thicknesses and have a reinforcement layer on each side to create more structurally stability. This layer also has fleece webbing attached to it’s surface to facilitate tile mortar bonding.
Their 1/2″ board is typically the one used in place of a standard tile backer board on the shower wall.
Without any waterproofing membrane attached, this board has a .36 perm rating. With a perm rating under .5, it can be used as a tile backer for steam showers installations according to the Tile Council of North America.
There is also a series of Kerdi Board prefab shower niches that are designed to be tiled.
Schluter also sells a foam shower base (or shower tray) that dominates the prefab shower base market.
This base is fixed to the subfloor via unmodified thinset mortar (explained in Kerdi membrane section).
This base does not have a tile bonding surface attached to the surface of the foam like a few of the others do. The top surface is the where the Kerdi membrane is attached with unmodified thinset mortar.
It also comes with a custom drain that has a built in bonding flange for the membrane to attach to.
The Durock pre-sloped foam shower trays are part of their shower system which includes the waterproofing membrane, pre-formed corners, pipe and valve seals and foam shower curb.
This shower base is similar to the Schluter base and many others in the sense that there is no tile bonding material attached to the top surface to facilitate mortar bonding. Their waterproofing membrane must be attached to it’s surface before tile can be placed.
It also comes with a custom shower drain specifically designed for this system so it integrates easily with their waterproofing membrane.
Their trays come in interlocking sections to allow for some ability to customize the size of your shower base. This is a relatively unique feature amongst the competition.
Durock also makes foam tile backer board panels, benches, and ramps. Their shower niche product is (surprisingly) not constructed with foam but rather ABS plastic. It also has a fleece covered surface so that a standard thin set mortar can be used to bond the tile to it’s surface (unlike it’s plastic competitors).
ProBase is unique among it’s competitors because it has a fleece covered membrane bonded to it’s surface. This fleece allows for extremely secure mortar & tile bonding along with decoupling.
The fleece coating means that no additional membrane attachment is required for tiles to bond to it. The custom drain assembly also bonds easily to its surface, maintaining the integrity of the membrane.
Noble also has a selection of foam shower niches and benches.
Wedi has a whole range of foam shower bases, backer board panels, benches, niches and thicker building panels.
These products are unusual because they are some of the very few products in the industry that have a cement coating on their surface to improve mortar and tile bonding.
This means that the surface is tile ready without any additional membrane attachment required (as with Schluter, Durock shower bases).
The Hydro-Blok system is very similar to the Wedi system and includes all the same of prefab foam products.
Another similarity is it’s cement coating. These products also install and integrate with the waterproofing membrane and shower drain assembly, just like Wedi.
This Contractor’s Opinions and Preferences
My simple answer for the best waterproofing method available for your shower would be to use a sheet membrane with the lowest permeability available.
I prefer to use Wedi Subliner, Durock sheet membrane, NobleSeal TS, or Kerdi DS, because they have the lowest perm ratings.
Follow the manufacturer’s directions and make sure all the joints and corners are sealed with the proper membrane components.
That would be my simple recommendation if you would like the easiest and safest protection against moisture problems down the road.
You didn’t think I was going to leave it at that , did you?
Of course there are many different waterproofing techniques and materials that you may be considering so I will also be providing my perspective on a few of these that I feel are important.
Problems With Liquid Waterproofing?
There is generally nothing wrong with liquid waterproofing membranes for shower waterproofing, but I prefer not to use them and I would recommend that you not use them either.
The reason for this is because they basically require perfect application. The waterproofing integrity of this membrane relies on a even thickness of material applied uniformly across the entire surface of the shower.
In my experience, perfectly uniform application is difficult to achieve even if you’re skilled with applying this type of membrane.
As well, most liquid membrane application instructions suggest that it is not necessary to apply reinforcing tape in the corners and seams. This questionable advice also contributes to thin areas in the membrane as the liquid tends to recede into gaps and crevices.
There is also a tendency for pinholes to form in the surface of the membrane as it dries. This is mainly due to air bubbling from the backer board when it has not being appropriately sealed (bonded) before application.
The Water Vapor Sandwich
The reality is that at least one of the walls of your shower will likely be on an outside wall.
This creates a problem with your modern shower waterproofing strategy because in addition to the membrane that you apply over the backer board, there is also usually a sheet of vapor retarder plastic behind the backer board to protect the inside of the stud wall from moisture.
Although it is important to severely limit moisture from making it into the wall, this two layer approach allows the moisture to be trapped between these two layers and condense on the plastic layer beneath.
This causes mold growth, deterioration of the backer board, and can lead to eventual failure of the entire wall assembly.
In other words, a terrible idea.
A Better Approach to Shower Wall Waterproofing
I would recommend you first remove any vapor retarder plastic sheet or felt from the stud surface on all the outside shower walls. The low perm waterproofing membrane (Wedi, Durock, NobleSeal TS) applied on the backer board surface will be the only layer of waterproofing required for this wall.
Because there is now only one waterproofing layer, this eliminates the vapor sandwich problem altogether.
If this technique is used, and your outside wall is adequately insulated, any trace amounts of moisture that pass through this membrane can harmlessly dissipate within the stud cavity instead of being trapped by a plastic vapour retarder sheet.
No more condensation, rot and mold. Problem solved.
Shower Niches – The Weakest Link
After reading about all the problems that can and do happen with outside shower walls, I think most of you would guess that it is always a risky move to install one in an outside shower wall.
A preformed foam shower niche can be a used as a great defence against long term leak issues into the shower wall, but they will never entirely eliminate moisture from moving into the stud space (see my discussion of perm ratings).
When a niche is mounted in an outside wall, this problem is compounded because the niche installation requires that some of the insulation be removed to make room for it.
In a outside wall that is probably already too thin for an adequate insulation thickness, the moisture moving into the stud cavity behind the niche has an extraordinarily high risk of condensing into water. This means mold growth and other problems.
A way to combat this would be to increase the thickness of the wall so more insulation can be installed behind the niche, but this is often not a practical option.
The bottom line is…. I would recommend that you not install your tile ready shower niche in an outside wall.
But if you do insist on doing so, the best solution would be to install a shower niche made from material that is impermeable to moisture, like a finished stainless steel niche. If moisture can’t get through it, there’s no risk of condensation behind it.
The Revolutionary Shower Base
Yes, I am calling the foam shower base revolutionary because of all the major problems that it solves in the modern shower. However, there are some conditions.
If you read about the problems with the old school shower base engineering in the first section of this post, you should be able to appreciate the awesomeness of this new technology.
The reason it is so awesome is because the shower waterproofing membrane is now directly under the tile, on the walls as well as the base.
Prior to this technology, the shower base was an engineering nightmare. Now, no significant moisture makes it into the base material so there is no concern about rotting and molding of the mortar as well as the continuous expansion and contraction of the base assembly.
Because no moisture makes it in or around the shower base, there’s also no need for a subfloor preslope or a redundant drainage pan underneath your shower base, as was required in the past.
I think I have made it clear that I do indeed think these foam shower bases are great. But this is really more about the time savings it offers the installer, rather than about the material itself.
What I am really most excited about is the new “surface sealing” waterproofing membrane technology (undertile waterproofing) which has single handedly solved all the problems of traditional shower bases.
You can be equally successful installing a mortar shower base instead of a foam one if you have a little bit of skill and some time to do it (a much cheaper option).
You will simply need to install a membrane over your mortar base to achieve the all important waterproofing barrier.
When More Waterproofing is Not Better
What you SHOULD NOT DO is assume that since one waterproofing strategy for the shower base is good, than two strategies will be even better.
First of all, I have to say that the “undertile” waterproofing membrane technology was created to eliminate the need for a drainage pan below the shower base. Period!
Installing a subfloor preslope and a shower pan liner and drain assembly is simply a lot of extra work with no benefit whatsoever.
In fact, if you are using a sheet membrane over the shower base with this type of traditional drain assembly, you will be violating the most important waterproofing element of this system and causing an intentional breach.
The two step drain that must be installed with a traditional shower pan is not compatible with a surface sheet membrane because there is no membrane bonding flange on these drains.
That is why there will always be a breach in the membrane around the shower drain if you install this type of drain instead of the custom integrated drain assembly that is sold with your sheet membrane system.
If you decide to go ahead with this pointless exercise against my advice, water will get between the drain and mortar slab, allowing the mortar base to saturate, trapping water under the sheet membrane.
This may not result in any damage to your framing (assuming the shower pan functions properly), but it will have some interesting and undesirable long term effects, I can assure you.
Bottom line is….. Decide on one system or the other. Never use both together.
Best Foam Shower Bases
If you read my overview of foam shower base features above, you will recall that I mentioned only two products that have a cement layer bonded to their surface. Wedi and Hydro-Blok.
These shower bases are my favorite by far and in fact, the only ones that I will use. If they are not available, I will choose to lay a mortar base instead.
As much as I love the time savings all of these bases offer, I am not at all comfortable with the bare foam bases, for a couple of reasons.
Firstly, bare foam will not bond to a traditional thinset mortar. What this means is that even thought these bases are fully waterproof, you cannot apply mortar and tile to their surface because they simply won’t stick.
That is why all of the bare foam products require a membrane to cover their entire surface before it is ready for tile. What is not often recognized is that the mortar used to “attach” this membrane does not actually adhere to it.
The mortar simply floats over the foam base and serves to stiffen the surface somewhat making it less vulnerable to deflection or point source damage.
The cement covered shower bases on the other hand, offer a completely waterproof and ridiculously rigid bonding surface for mortar and tile bonding, with no need for a additional membrane.
Don’t Drop the Scrub Brush!
And speaking of point source damage….. This is my next complaint about the bare foam shower base products. You only need to look it up online to see what I am taking about.
Even with a mortar imbedded waterproofing membrane laying over top of the bare foam base, it is still considerably vulnerable to impact damage.
This damage can technically occur during installation or even after installation if you make the mistake of using 1″ mosaic tiles for your shower base tile (not recommended).
See my shower remodel dangers post for more info on this scary issue.
As a professional in the field of shower waterproofing, I am fascinated how this business continues to evolve and expand. As such, I tried to write something that provides timely and actionable info for the average DIY installer as well as the seasoned professional.
I really hope that you were able to get something from it. Please let me know what you think in the comments below.
I am also interested to hear about your own experiences with shower waterproofing, good and bad.
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