The Importance of Waterproofing Behind Your Shower Walls
by：Heng Xing 2020-06-09
When most people enter their tile shower they rarely think about the behind the scenes process that went into making that shower work correctly. Unfortunately some contractors will use this to their advantage to cut corners and save a couple bucks. I have to say most contractors are trying to do a good job, even though some of them never learned the correct procedure and why these processes are important. The best way to find a good tile contractor is to ask them to explain the theory. If they can tell you how it works behind the scenes, it is more likely you will get a good job. If your friends refer somebody to you it is still OK to ask these questions, after all what do your friends really know about the foundation of a tiled shower? They may have found a contractor who is nice and easy to work with and their brand new shower looks great, but if you don't want to fight mildew in 6 months and for the next 20 years you will ask a couple of questions. So let's start at the beginning and explain common language and theory of a tile shower. First you have what is called a shower pan. This is a completely waterproof section that covers the shower floor and up the walls about 10'. This is either a hot mop, (which is a number of layers of tar paper, hot tar, tar paper, hot tar and so on) or it can be a PVC membrane that is folded into the corners and over the dam. The most important part of this for you the homeowner to know is of course it's completely waterproof but also that it has what is called a sub-pitch. A proper sub-pitch is simply a float of cement or similar product under the pan that creates a flow to the drain on top of the shower pan. This is important because, say for instance your shower pan is flat (no sub-pitch) water will travel through your grout and make its way to the pan while showering. If this water forms a puddle under your tile floor instead of flowing towards the drain it becomes stagnant and soon will become mildew in your grout. With a sub-pitch the water that makes its way to the pan will continue to flow towards the drain always being replaced with fresh water. It is much like the difference between a pond and a creek. Next you have a vapor barrier that is applied to the walls directly to the wood studs. This is normally a paper that has a tar trapped in the middle. This paper keeps moisture out of the walls. Why is this important? Not a lot of water penetrates the shower walls, but the substrate (the substrate is whatever surface your tile is stuck to, backer board, cement float, etc.) this surface will get moist. Moisture will move from substrate toward the inside wall, out through the grout and down towards the pan, without vapor barrier paper you will get small amounts of water into your wall cavity. So you say 'why should I worry about such a small amount of water'. The reason is when you get a drop of water inside your wall every time your shower is used, those drops add up because your wall has no ventilation for evaporation, so eventually the wood is always moist. Do you know what loves moist wood? Termites, they love these conditions because they never have to travel back to the ground to get a drink, they can just keep eating. It would be like you and I never having to go to the grocery store. Think of how productive we could be if that were the case. Well that's the theory of waterproofing behind your shower walls. When you stick to these guidelines your new shower has the best chance of looking great for many years, without extreme maintenance.