Building a Shower Pan With Vinyl Liner

by Tuffys Dad

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Intro: 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.

9 Comments

Icelandian 2 years ago

Nice work. I'm doing the same currently, but I see a lot of division on whether a pre-slope is necessary or not. Since you included one I assume you prefer it. Has that changed since you posted? Thanks

Tuffys Dad 2 years ago

I have seen many pans built and have built many myself. Whether vinyl or mopped, the preslope is always installed. This is because if water seeps past the tile and mortar past the top slope onto the waterproofing (vinyl or tar), the preslope directs the water to the weep holes in the drain assembly. This type of leaking is admittedly rare, and is generally because of poor installation, damage, age, etc. However, it is the last possible way to divert water in the event of a leak. I hope this helps, and best of luck in doing this job.

Icelandian 2 years ago

Thanks for the quick and detailed response. I was on the fence and your answer swayed me. I was hesitant because my drain is close to one of the short sides of what will be a 4’x6’ shower, so the far wall will add 1-1/4” for the pre-slope then again for the top slope. I think the only thing I may modify is to add another 2x4 (4 total) to the curb, which is on the far side from the drain.
Thanks again. (depending on how it turns out I may do an instructable on it too.)

Tuffys Dad 2 years ago

Yes, you may need a higher curb to accommodate the distance. But when done it will look and work great! Cheers.

Icelandian 2 years ago

Thanks, appreciate the encouragement.
Sorry one more question - Do you continue the slope on the outer walls or do you draw a straight line between each pair of corners. Image attached below is a 3D model of my preslope with a uniform slope from the drain. The blue line would be that straight line mentioned.

Tuffys Dad 2 years ago

What I do is mark a level line on the walls and curb for 1/4" per foot slope (as you did). I don't go diagonal but side-to-drain). Then you can build up a nice ledger of mortar at that wall line, and mortar at the drain (at the height required for mounting the drain assembly to allow the weep holes to be level with the vinyl membrane as I mentioned before), and trowel and screed inwards from the wall mortar ledge to the drain mortar. Also, if you can't move the drain, there may be some interesting drain assembly options that may offer solutions (e.g., larger drain area so you can move it away from the wall). It looks odd on the CAD drawing, but it will drain properly and won't be noticeable when finished. Hard to help without seeing the job, but I hope this helps...

Hamlin57 8 years ago

Thanks, well written. You gave me the confidence to build my own shower pan!
I am doing a complete remodel of a 950 sq. cottage with walkout basement, again THANKS.

Tuffys Dad 10 years ago

Thanks - keeps me home and out of trouble!