The next step for the walk-in shower was applying membrane to waterproof the shower floor. The traditional way of waterproofing a shower floor is with a solid membrane that installs directly over the sloped mud base (“Preventing Leaks in Tiled Showers,” Oct/16). But because this shower was so large, we opted for Schluter’s Kerdi membrane, which is installed with unmodified thinset spread on top of the mud base, (or in this case over the Ditra Heat membrane that I installed over the mud layer). Kerdi membrane can be installed in pieces as long as the pieces overlap by at least 2 inches, with every layer fully bedded in the unmodified thinset.

Bed the Drain First

The linear drain at the back of the shower (also made by Schluter), comes with Kerdi membrane attached around its perimeter. I started by spreading unmodified thinset around the drain. Then I unfolded the membrane from around the drain and pressed it into the wet thinset.

 Bed the Back Wall of the Shower