In part 1 of this series on curbless showers, we discussed how to modify the floor framing to accommodate a whole-room mud-set pan. In this second part, we'll look at the prep work required prior to setting the floor tile.
The most important goal to achieve in creating a shower pan is to make sure it's waterproof. In order to accomplish this, you have to have good drainage. After the subfloor has been installed over the lowered joists, the tile guy begins to work his magic. The first step is to lay a mortar base, which is the foundation or support for the floor system. It's critical that the entire mortar base is sloped slightly towards the shower drain, so any water that penetrates the porous finish floor above finds its way safely out of the room. In the small pan area where the actual shower is located, he creates a more radical slope that can handle the high volume of water. To make the floor waterproof, a membrane is laid over the entire mortar bed floor and vertically up the adjacent walls. Because stone, grout and mortar are porous, they need help in collecting water that will inevitably flow through them. Because the foundation underneath is sloped, any water that does make it through is collected by the membrane and sent directly to the drain. If the floor is going to be heated, the electrical cable is installed next. Once both the membrane and wire is in place, the tile setter pours a self-leveling compound over the entire floor, sandwiching the cable in-between the membrane and self-leveling material. Because it dries perfectly level, it gives the surface a “normal”, balanced feel. The only exception is the actual shower area, which must have a sloped finished surface to collect the water.
Prep work in any trade is generally the most time consuming and important part of the job. This could not be more true than with a whole-room curbless shower system. The reason? You're dealing with an open water source that has free reign in the room. When done correctly, these systems can provide decades of service.