How To Install A Mortar Shower Pan Membrane Liner

Introduction: Building a Shower Pan With Vinyl Liner

This is the finished bathroom I built a few years ago which includes a large walk-in shower. There are many construction steps involved in the build, but here I will discuss one of the earliest steps -- building the shower pan. A shower pan works as a waterproof dam sloped toward a drain. There are several ways to make a shower pan waterproof -- a pre-made pan can be used, made of plastic or concrete. Pre-made pans are usually available only in certain standard sizes. Another method involves a "hot mop" of waterproof rubberized material professionally installed. The method I employ here uses a very thick waterproof vinyl material that lines the bottom of the shower with a sloped mortar bed formed above. It is within the ability of a skilled homeowner to utilize this method. Simple concrete tools are required -- several trowels, a level, and a way to mix the concrete "deck mortar".

Step 1: Build the Walls and Expose the Drain

The shower walls have been framed like any other wall with 2"x 4" studs, generally 16" on-center, and pressure-treated sill plates (the lumber that sits on the floor). During the "rough plumbing" of the shower and tub, the drain pipe ends were each encased in plastic boxes, so when the slab was poured a void was created surrounding the end of each drain pipe. This photo shows the shower walls built (with design features like a space at the tops of walls and glass block "windows"). The drain boxes are also visible, with one inside the shower walls and the other for the future tub drain. The boxes will be cut away to expose the drain pipes inside.

Step 2: Build a Shower Curb

A shower curb is built with pressure-treated lumber. The curb is bolted into the slab with concrete anchor bolts ("Red Heads") and the top board covers the bolts and nuts.

Step 3: Construct a Trap and Place the Drain

Here the box has been cut away and a p-trap installed that will sit below-grade. I have also set in place the two-piece drain assembly (my preference are Ebbe drains for superior design and excellent hair-trapping). I will set the height so the lowest part of the drain (the round part under the bolts) is app. 1/4" - 1/2" above the slab. I then wrapped the pipe with pipe wrap before filling the space with concrete.

Step 4: Fill the Void

Here I have filled the void with concrete and feathered it smooth. The lower drain part is app. 1/4" above the slab and is covered with duct tape to keep out debris.

Step 5: Block the Lower Shower Wall

Shown here is the blocking and plywood installed about 12" high from the bottom of the shower. This is done to provide support for mortar that will go partially up the wall to form sides of the dam.

Step 6: Trowel a Pre-slope

Next, a "pre-slope" is troweled to sit below the vinyl material. The slope is formed to the standard 1/4" per foot. Measurements are made from the drain extending to each wall, then 1/4" per foot is calculated for the length, and marks are made on the walls to correspond to the necessary height. Deck mortar is used (sand and cement only - no aggregate) and the slope is troweled from the drain to the levels marked on the walls. A level is dragged around the area to confirm the slope and smooth it (some levels are marked with the 1/4" per foot position).

Step 7: Finish the Pre-slope

Here is the finished pre-slope. The upper portion of the two-piece drain is in place to keep out debris. The vinyl will go over the pre-slope, the idea being that if water gets through the tile grout, and through the upper mortar bed, it will hit this vinyl and still exit into the drain via weep holes along the rim of the lower drain piece.

Step 8: Install the Vinyl Sheet

Vinyl sheet especially made for shower pans is available from several manufacturers. The sheets are quite thick -- about 40 mil. and pre-made pieces for curbs, corners, etc. are sometimes available. The glue used is also specifically designed for vinyl material. First, the drain pieces are separated and the vinyl is laid into the bottom of the pan. Then small slits are cut where the drain bolts will hold the two drain pieces together. Assemble the two drain pieces -- one above and one below the vinyl -- and bolt together. Coat the bolt holes with clear silicone before tightening the pieces together. The large drain hole is not cut open yet. NO OTHER HOLES are ever put into the vinyl inside the pan. Corners are made by folding the material and nailed the fold at the top with a single roofing nail. The curb is made by cutting and gluing vinyl pieces with plenty of overlap and plenty of glue. The curb piece is only nailed at the back (outside) of the curb.

Step 9: Install Mortar Forms

To form a nice straight top edge of the pan I used strips of 1/2" sheet material (OSB or plywood) that is the same thickness as the tile backer board I'll use on the shower walls -- this will provide a smooth transition for the tile. Before I screwed in the strips I cut wire lathe for the short vertical surfaces to keep the mortar in place. The lathe is carefully cut to stop about 1" from the pan bottom (no contact with the vinyl). The OSB strips are leveled of course before screwing in place. The curb is also covered with lathe and simply wired to the wall lathe to keep it in place. The plywood form on the outside of the curb was made to trowel the curb flat and and make a clean edge.

Step 10: Troweling the Pan

Before troweling the pan I put small pebbles around the weep holes in the drain. I adjusted the height of the drain top above the vinyl to get about 3/4" of mud plus the thickness of the tile used. The idea is that the drain top is flush with the finished tile. I them marked the perimeter mortar height using the same 1/4" per foot from the drain top. Deck mud is again used; troweling starts with the shower floor -- just like the pre-slope, using a level to smooth it and checking the slope. then the walls are troweled, being sure to pack the mud into the wire lathe then smooth and join the bottom and side walls as shown in this photo.

Step 11: Final Pan Mortar

The finished pan still setting up with form boards in place. They are gently removed after a few days.

Step 12:

Once the form boards are removed a nice clean edge is left for mounting the tile backer board. Cardboard is put on the floor to protect it for the rest of the job. If you like this instructable, I have a book on Amazon called, "Owner-Builder: How an Amateur Built a Professional-Grade Home Addition" by Bill Mathews. Check it out, and thanks for looking.

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