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Shower Membrane Waterproofing – DIY’ers Definitive Guide

Man stepping in Redgard bucket- Shower Membrane post

Steve Gehrmann is a remodeling contractor (SKG Renovations) as well as a partner in Redblock Industries

If you have completed or are planning to complete a shower remodel, you’ve likely wondered about shower waterproofing. Hopefully you’re not as confused as the cartoon man in the picture, but wherever you’re at in your investigation, I think you’ll find this post useful.

One of the MOST IMPORTANT steps in any shower remodel is waterproofing.

In this post I, Steve of SKG Renovations, 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.

Ok, let’s get into it!

Topics Covered:

Brief History of Shower Waterproofing

Fixing the Leaking Shower

Types of Waterproofing Membranes

The New Age of Shower Waterproofing Products

This Contractor’s Opinions and Preferences

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’s always had serious limitations such as inconsistent coverage, varying degrees of moisture permeability, AND that it served as a moisture condensation surface where black mold could grow (see image below).

Verschoor Bath demo showing black mold behind old drywall

Image Courtesy of SKG Renovations

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

Image of Schluter Kerdi Waterproofing Membrane Roll (Amazon link)
Schluter Kerdi Waterproofing Membrane
Ad: The above image is an affiliate link.

The sheet membrane is exemplified by the brand leader in the industry, Schluter Systems and their Kerdi waterproofing membrane (see above), 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. The most popular of these is Kerdi Board by Schluter Systems.

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.

If you’d like to read more about foam backer boards (and other tile backer boards), check out my Shower Tile Backer Board DIY Guide.

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.

Wedi Subliner Dry:

Image of Wedi Subliner Dry Waterproofing Membrane roll (Amazon link)
Wedi Subliner Dry Waterproofing Membrane
Ad: The above image is an affiliate link.

This sheet membrane system was engineered for the high water vapor environment of steam shower. The difference is that this membrane has an 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 by USG,

Image of USG Durock Shower System- Waterproofing Membrane Roll (Amazon link)
USG Durock Shower System- Waterproofing Membrane
Ad: The above image is an affiliate link.

Durock sheet waterproofing membrane has 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 Company:

Image of Noble ValueSeal shower waterproofing membrane (Amazon link)
Noble ValueSeal shower waterproofing membrane
Ad: The above image is an affiliate link.

Noble has a few good sheet membrane products designed for shower waterproofing. Their ValeSeal membrane is one of their less expensive membranes with a perm rating of “less than 0.5 perms”, which makes it slightly better than the Schluter Kerdi membrane, the most popular shower waterproofing membrane out there.

I prefer their NobleSeal TS membrane because of it’s ultra 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.

Noble also offers a range of extruded polystyrene foam products including preformed shower benches, preformed shower niches, and shower bases.

Schluter Kerdi:

Image of Schluter Kerdi Waterproofing Membrane Roll (Amazon link)
Schluter Kerdi Waterproofing Membrane
Ad: The above image is an affiliate link.

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 its 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

Redgard Waterproofing Membrane by Custom Building Products:

Image of bucket of Redgard Waterproofing (Amazon link)
Redgard Waterproofing Membrane
Ad: The above image is an affiliate link.

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.

Mapei Mapelastic Aquadefense:

Image of Mapei Mapelastic AquaDefense bucket (Amazon link)
Mapei Mapelastic AquaDefense
Ad: The above image is an affiliate link.

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).

Laticrete Hydro Ban:

Laticrete Hydro Ban waterproofing bucket (Amazon link)
Laticrete Hydro Ban
Ad: The above image is an affiliate link.

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:

Schluter Kerdi Board

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.

Kerdi Shower Base:

Image of Schluter Kerdi-Shower Kit (Amazon link)
Schluter Kerdi-Shower Kit
Ad: The above image is an affiliate link.

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 has always always been a bare foam shower tray with no tile bonding surface attached, but this has recently changed. They now have an integrated waterproofing membrane laminated to the top surface. As such, there is no longer any need to attach the Kerdi membrane to its top surface as there was in the past.

The Kerdi Shower Kit also comes with a custom drain that has a built in bonding flange for the membrane to attach to.

Durock shower trays and panels by USG:

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 by Noble Company:

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 Shower Systems:

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).

Hydro-Blok Shower System:

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.

More Details….

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.

A good way to limit this problem is to apply a bonding agent to the surface of your cementitious backer board before applying the liquid waterproofing membrane.

Image of Weldbond Universal Adhesive bottle (Amazon link)
Weldbond Universal Adhesive
Ad: The above image is an affiliate link.

I use Weldbond for this purpose (pictured above) because it’s easy to use, non-toxic, economical, and readily available.

You simply dilute it with water (follow the directions for using as a bonding agent), and apply one coat to the tile backer surface using a roller and brush. Make sure you cover the entire surface where you will be aplying yor liquid waterproofing.

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.

If you don’t trap the moisture, there’s no condensation, rot and mold. Problem solved.

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 a shower niche 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 an 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 much less risk of condensation behind it.

If you’d like to know more about the mistakes that are often made when installing a shower niche, check out my 5 BIG Shower Niche Install Mistakes post.

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.

Conditions……..

I think I have made it clear that I do indeed think these foam shower pans/ bases are great. But this is really more about the time savings it offers the installer, rather than about the material itself.

What I’m 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.

If you want a bit of a challenge and would like to save a bunch of money, you can always try installing a mortar shower pan instead of a foam one. 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.

My reasoning?

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 an 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 post for more info on this scary issue.

Wrap Up

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.

This post is for information purposes only and should NOT be interpreted as professional advice. You should always consult a licensed local contractor before undertaking any remodelling work in your home. Click here for my full Personal / Professional Disclosure.

There are 129 comments on this post:

  1. Avatar photo

    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?..

  2. Steves User Profile Image

    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

  3. Avatar photo

    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!

  4. Steves User Profile Image

    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

  5. Avatar photo

    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.

  6. Steves User Profile Image

    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

  7. Avatar photo

    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!

  8. Steves User Profile Image

    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

  9. Avatar photo

    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.

  10. Steves User Profile Image

    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

  11. Avatar photo

    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.

  12. Steves User Profile Image

    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

  13. Avatar photo

    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?

  14. Steves User Profile Image

    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.

  15. Avatar photo

    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 !

  16. Steves User Profile Image

    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

  17. Avatar photo

    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

  18. Steves User Profile Image

    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.

  19. Avatar photo

    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!

  20. Avatar photo

    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.

  21. Avatar photo

    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.

  22. Avatar photo

    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.

  23. Avatar photo

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

  24. Steves User Profile Image

    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

  25. Avatar photo

    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?

  26. Steves User Profile Image

    Hi John,

    Thanks so much for your kind words. I’m glad you got something out of it.

    Good luck on your project!

    Steve

  27. Steves User Profile Image

    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

  28. Avatar photo

    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.

  29. Steves User Profile Image

    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

  30. Avatar photo

    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

  31. Steves User Profile Image

    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

  32. Avatar photo

    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?

  33. Steves User Profile Image

    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

  34. Avatar photo

    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?

  35. Avatar photo

    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.

  36. Avatar photo

    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.

  37. Avatar photo

    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.

  38. Avatar photo

    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

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