Shower Membrane Waterproofing – The Definitive Guide (for 2018)

by | Last updated Mar 18, 2019 | Shower Remodel

So you’re remodelling your shower… and wondering about waterproofing with a shower membrane?


This post brought to you again by Steve of SKG Renovations (Steve’s Bio), will inform you how to avoid leaks in your new shower remodel. I will explain how a shower membrane works, the different types available, and why they are important.


Not just important actually…but VERY important!


You may not have put that much thought into the subject of shower waterproofing. And if you have, you might have assumed that waterproofing is standard procedure; a “default” for all bathroom remodelling contractors.


But here’s the 1st problem:


It’s not always a standard procedure. Shower Membrane products can add cost and complexity to the shower remodel. And some old-school contractors might wonder why they would change their ways and start using these new products when their old methods worked perfectly well.


So here’s the 2nd problem:


Many of the old-school shower installs could start leaking and breaking down after their first use but nobody would really notice. This is a slow process that starts out with tiny amounts of water getting through the tile and breaking down the drywall over time. This is especially true in the corners and on outside walls.


Read on to get the critical knowledge you need to tackle your own bathroom remodel project, whether it’s a DIY shower remodel or a contracted job.


And at the end of the post there is a bonus tip on how to easily and safely incorporate a shower niche into your shower wall without breaching the membrane.

Old School Shower Membrane


Lets start out with a little history on the practice (or lack of) shower wall waterproofing.


A few years ago (more like a couple of decades ago), the waterproofing shower membrane was a seamless rubber liner attached to the base framing. It was designed only to waterproof the shower base and lower section of shower wall, nothing else. A structural mortar base was then laid on top of the liner and tile laid on the mortar base.


The objective was to keep water that may penetrate the tile surface from eventually leaking through and into the supporting framing below. This method is still used today by some contractors believing that it has always worked well. And if the membrane was installed properly, it did indeed keep the water from entering the framing beneath your shower base.


So…. it’s all good right?

….. Well, not exactly.


If no immediate breach occurred at the shower drain (which was also fairly common) the flexible and relatively thick rubber membrane would flex and compress slightly whenever there was weight on the shower base (shower pan). Over a very short time, this movement (tile assemblies hate movement) would cause fractures in the shower base tile, mostly at the corners and around the drain.


At this point of deterioration, it doesn’t take long before water makes it’s way down, between the mortar base and the rubber liner, and a cascade failure results. The mortar starts disintegrating and mold begins to grow. A nasty mess to be sure, and a complete failure of the assembly as a whole.


So the rubber shower liner was a good idea in principle, but not in practice. There needed to be a new approach to bathroom waterproofing.

A new approach


Engineers of shower systems realized that the old system needed to be replaced so they set out to develop a waterproof shower membrane for tiling; a layer between the wall surface and the tile that would decouple the tile layer and protect the wall from moisture.


Even without the problems associated with the rubber shower tray liner, the tiling assembly in a shower installation is a complex and problematic one.


It’s complexity has to do with the fact that the shower floors and walls will always expand and contract at different rates than the tile assembly laid on top of it. This means that there is a virtual guarantee of grout line cracking and tile de-lamination if the tiles are solidly attached to the substrate (the shower base or shower wall board). This effect is most pronounced in the corners as well as around the shower niche and shower drain.


Luckily the solution was quite simple (and elegant):


Disconnect the tile assembly from the substrate with a membrane. This way the tiles and substrate can bond to the shower membrane instead of each other, allowing them to move independently. Now the top surface assembly (tile,  mortar and grout) can expand and contract together (in a safe manner) reducing any chance of cracking. That means water can’t penetrate and get in where its not supposed to be.

The New Shower Membranes


The new style of waterproofing shower membranes come in two main types, sheet and liquid.

Sheet Membranes


The sheet membrane is usually made from a mix of polyethylene and polypropylene. It comes in rolls and can be applied to the shower floor or walls with an adhesive, thin-set mortar, or some form of adhesive backing, depending on the manufacturer. The tiles are then applied directly to the outside surface.


The bonding surface on both sides of sheet membranes, is a fleece-like material that allows mortar to bond firmly to it. However, the mortar/ adhesive does not totally immerse the fleece “hairs” on both sides of the membrane, allowing the base of the hairs and the waterproof poly layer of the shower membrane to be free to move.


Because the sheet waterproofing membrane is suspended between the substrate (backer board) and the tile assembly, the tile layer is effectively decoupled from the wall – floating over the wall, in a sense. Although counterintuitive, the suspended tile surface can also carry high loads due to it’s brilliant engineering.


The poly layer also acts as a moisture barrier so water cannot penetrate the substrate to any significant degree. The shower membrane manufacturers also provide specially designed seals for your shower fixtures. These seals bond to the sheet membrane and will seal the shower wall at all the points where the plumbing and valves comes through the wall.

shower membrane - Loewen-bathroom-shower-Kerdi-whitened-scaled-to-400W-80jpg
shower membrane - Loewen-bathroom-shower-finished-whitened-scaled-to-400W-80jpg

Liquid Membranes


The liquid style of waterproofing shower membrane works very similar to the sheet style in that it decouples and blocks moisture. The difference is that it is applied with a brush and/ or roller on a pre-bonded surface. A waterproof paint, so to speak.


If adequate coats are applied it can perform very similar to the sheet membrane, except the material securely bonds to both the substrate and the tile layer. The thickness and flexibility of this rubber-like substance allows the two surfaces to be effectively decoupled & move independently, even if they are technically coupled.


The rubber-like consistency of the finished shower membrane surface also acts as an effective moisture barrier.


Similar to the sheet style waterproofing membrane, the tile surface over a liquid style shower membrane can also carry high loads without significant compression.


Two popular types of liquid shower waterproofing products are RedGard and Mapei AquaDefense.

Important or not?


Do we really need to be waterproofing the shower wall with a shower membrane?


Some of you DIY’ers out there (or even some professionals) may question the need for a shower membrane because they have torn out a 1970’s tub/ shower that looks perfectly fine. The drywall backer board is still OK and there doesn’t seem to be any significant water penetration.


To be fair, there are some tiled tub/ shower assemblies that were built well enough to make it through the years without a waterproofing shower membrane. However, examples like these are few and far between, and all of them were tub/ shower installations, not showers. They also would have been cared for gingerly over the decades and none with “built-in’ features like soap trays, which basically invited water into the wall cavity.


Most, if not all showers built during this period were doomed from the start, and are only distant moldy memories in most peoples homes.

Shower Membrane = Lifetime Shower


With new shower membrane technology, you can expect a properly installed shower assembly to last as long as you care to keep it.


The problem of de-lamination of tile, and water seeping under your shower mortar base are a thing of the past. Even the heaviest of people cam stomp around in their shower without the worry of the tile deflection that caused grout cracking and leaks in the past.


A recessed area for soap in an old style shower assembly would have been an invitation for shower wall rot and mold growth. Now with new shower membrane technology, the trend of recessed shower shelves or “shower niches” can now be embraced without hesitation, although careful membrane application technique is still required.


So what is the best waterproofing membrane for your shower?


As a contractor I have used all three of the most popular shower waterproofing membranes, Schluter KerdiRedGard and Mapei AquaDefense. In my opinion all three are great options for waterproofing your shower wall during a remodel as long as they are installed according the manufacturers directions.



We mention the shower niche as a bonus tip because it is so commonly installed in a modern bathroom renovation, and it represents a potential breach in the shower wall membrane if installed incorrectly.


There are a few niches that are designed to bond to the shower membrane in a similar way that the shower fixture seals do. The  Redblock Shower niche is a good example of this type of finished niche. The M-Block flange  bonds the perimeter of the niche to the waterproofing membrane. The Redblock niche itself has a totally finished interior so there is none of the uncertainty related to a custom tiled niche installation.

Alternatively, the custom tiled niche requires the installer to be very meticulous in their application of the membrane to the interior surface, in order to avoid leaks. Membrane application to the interior of a tiled niche is a meticulous task, suited only to the most detail-oriented installer.

Don’t forget to leave a comment and tell us if you found the shower membrane waterproofing info useful. We would love to hear from you!