Installing a shower membrane ensures that your shower floor and enclosure will remain water-tight. A shower membrane is similar to a swimming pool liner. It is a special type of plastic sheeting that goes around the bottom of the enclosure and the shower pan to prevent water from seeping through gaps and crevices in the shower and into the underlying materials.
The lack of a shower membrane can result in rotting wallboard, mold, mildew, and rotten wood studs. In other words, big problems. It is a simple and inexpensive piece of material that will make all the difference in the life and performance of your shower. Here you will find some tips on installing a membrane in your shower enclosure. These instructions are based on the assumption that the concrete base has already been poured.
Step 1 - Measure the Membrane
Measure the shower pan. Install the membrane after the initial layer of concrete has set, but don't wait until it is totally cured. Generally, letting it cure overnight before installing the membrane is fine. Lay the membrane on the floor and transfer your measurements onto it. The membrane should extend between 9 and 12-inches up the side walls for the full amount of protection. Plan your measurements accordingly. Mark the measurements with a permanent marker and use a utility knife or scissors to cut it. Don't forget to cut out a space to accommodate the drain.
Step 2 - Fit the Membrane
Lay the membrane in the shower pan and adjust it as needed. Install the membrane before the backerboard. The membrane will bunch in the corners. It is important to wedge the membrane back into the space between studs and get it as smooth as possible. If there is a hump where a wad of membrane is, you will see it once the tile or surround is installed, so take some time to make sure it is done well. If you hang your backer-board first, leave .25-inch gaps in the corners.
Step 3 - Secure the Membrane
Use rubber cement around the opening in the liner next to the drain. Cement approximately 1-inch of the material to the shower pan around the drain. Finally, use the waterproof tape in the corners and around the edge of the membrane to seal it.
Step 4 - Finish the Shower Pan
Pour the final layer of concrete over the membrane, equal to the height of the drain. Smooth the final layer and let it cure. Have the drain height set at this point, as you will not want to have to adjust the height once the final layer of concrete is poured. Once the shower floor is complete, you are ready to finish the shower.