Avoid Shower Leaks – Ultimate Guide to Shower Membrane Waterproofing
Do you need a waterproofing membrane in your shower?
Many of you may not have heard of a waterproofing shower membrane, until your contractor installed one in your new shower remodel. For those of you that need a rundown of what they are and what they are designed to do, you’ve come to the right place. To give you some context and background, a brief overview on the traditional practices is important. We can then delve into the different types of membranes used, how they work, and why they are indeed very important.
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 & 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 water from entering the framing beneath your shower base. So…. it’s all good right? Not exactly….. If no breach occurred at the drain, which was also fairly common, the flexible, and relatively thick rubber membrane would compress slightly, every time anyone stood on the shower floor. Over a very short time, this movement (tile assemblies hate movement) causes fractures in the shower floor tile, mostly at the corners and drain. It doesn’t take long before water makes it’s way down, between the mortar base and the rubber liner, and a cascade failure ensues. 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.
A new approach
Engineers of shower systems realized that the old system needed to be replaced, and so begins the life of the waterproofing and decoupling membrane. Even without the problems associated with the rubber tray liner, the tiling assembly in a shower installation is a complex and problematic one. It 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). Luckily the solution is quite simple – disconnect the tile assembly from the substrate with a membrane. This way the tiles and substrate can bond to each side of the shower membrane but still move independently, while also keeping moisture out of the walls and floor.
Waterproofing shower membranes come in two main types, sheet and liquid. 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 is a fleece-like material that allows it to bond firmly on both sides. The result is that the membrane is decoupled, or “floating” between the substrate and the outer tile layer. This allows the tiles and substrate to move independently, yet the tile surface can still carry high loads. The poly layer also acts as a moisture barrier so water cannot penetrate the substrate to any significant degree.
The liquid style of waterproofing membrane works very similar to the sheet style in that it decouples and blocks moisture. The difference is that it is applied like paint on a pre-bonded surface. 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 also acts as an effective moisture barrier. The tile surface can can also carry high loads without significant compression.
Important or not?
Now that you know what a shower membrane is and how it works, you might still be wondering what is the big deal if you do not apply a waterproofing membrane in your shower. 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 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.
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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 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. There are also some waterproof “finished” niches that install easily & integrate with the waterproofing membrane for additional security.
For more information on shower niches, read this article: What is a shower niche
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