Tile contractor Tom Meehan: When I have a window in a shower stall, the most important thing to protect is the sill itself. There are two options to waterproofing a window. One is a liquid membrane, and the second is a waterproof backerboard. Here, I’m using a Kerdi-Board. This Kerdi membrane I’m going to apply is just an extra thing I like to do. The sill is the most prone area to water problems. To install the membrane, I use a very fine-tooth spreading trowel. I get a thin layer of thinset, and then I work the membrane down into it, push the thinset to the side, and press it down tight. I wrap up the corners so that I know the thinset is locked in the corners where the wall meets the sill.
Now that I have the membrane in, I can finish off the glass tile and install the sill. When I put the backerboard in here, I built the cement up on the back side to give it the proper pitch.
Now I’m going to install the marble slab. When using natural stone, you should always butter the back of it—especially if it’s white marble, because it’s translucent. With the sill in, I can tile the sides of the window. Anytime the tile meets the window itself I use a sealant.
Another thing I offer my clients is a shampoo niche. Many people are concerned about it being waterproofed, but if it’s done properly, there’s nothing to worry about. To do one properly, I’d rather not have it framed out beforehand. Once I figure out the coursing, I’ll cut through the cementboard, put in blocking, and caulk that in place. After that, I do cementboard; or, using just a waterproof liquid membrane, I’ll coat two coats inside the niche. The most important thing about doing a niche is that it has to be pitched back into the shower. When someone has a niche in a shower stall, it’s going to hold shampoo bottles and soap, and water is going to be spraying into it. If I do the proper waterproofing, there’s nothing to worry about.