A shower floor membrane, sometimes called a pan liner, catches all moisture that seeps past the floor tile and directs it toward the floor drain. In a perfect world, the tile floor would divert all the water toward the drain opening. However, in real life, small cracks form along the shower walls and next to the drain. Caulking does help seal these problem areas. Unfortunately, some water passes through these areas and reaches the pan liner. The membrane protects the building from water damage, mold, and mildew.
Acquire all necessary permits from your local building inspector before starting this project. Some communities require a permit for any plumbing work. Think about the permit as an insurance policy that protects a homeowner from non-compliant contractor workmanship. The shower floor installation portion of the project starts after a local building inspector approves the work, when applicable.
All quality work starts with a solid foundation. A tub drain penetrates the shower's subfloor near one wall, while the drain in a typical standup shower normally sits near the center of the floor. If the installer keeps the drain near one wall, he must consider the shower floor's slope. For instance: a tub measures 5-feet long, which would make the floor's mortar base approximately 1.25 inches thicker at the walls than it is near the tub's original drain opening. This would make the pitch between the new shower drain and the closest wall extreme.
To avoid this situation, the contractor must relocate the drain penetration. If the bathroom sits on a wood subfloor, the contractor simply cuts the new opening the same size and shape as the original and uses the cutout as a scab piece to fill in the old opening after finishing the plumbing work. Bathrooms sitting on a concrete slab require a little bit more work. To relocate the drain, a contractor must remove the concrete between the old drain location and the new one. He then cuts away the old trap, adds a section of drain pipe and installs the trap and shower floor drain assembly at the new drain location. This leaves a big gaping hole in the slab. Failure to repair the slab often leads to future shower floor settlement issues, such as grout cracks.
Consider the pre-slope the last line of defense against mold. When an installer fails to create a pre-slope, water collects on the pan liner in the problem areas. This leaves constantly wet areas under the shower floor for mold and mildew to grow.
A shower floor drain consists of three parts: a flange, clamp ring, and drain barrel opening. The drain flange mounts to the sewer pipe, the clamp ring holds the membrane in place, and the drain barrel holds the finished drain grate at the correct height.
Some larger showers require more than one section of membrane to cover the floor and wall overlaps. In these cases the installer must create a long-lasting waterproof seam.
© 2019 Bert Holopaw