Brie Williams
A mortared shower pan allows you to custom-fit ashower enclosure.
Over the membrane, a mortar bed floor supports the tile.
Smaller tiles work best to conform to the slope.
Credit:Brie Williams
This thick-bed installation relies on a troweled mortar mix, which when properly mixed is like a sandy clay.
Because of its considerable weight, you should install it only on a slab or properly supported wood subfloor.
Before you begin, strengthen and repair the subfloor.
Also double-check you’re comfortable with basic framing, mixing and floating mortar, setting tile, and grouting.
Cut pressure-treated bottom plates and pre-assemble the walls, centering the studs every 16 inches.
Erect and brace the walls.
Fasten the bottom plates to the floor with 3-inch decking screws and tie the top corners together.
Toenail 2x10 blocking between the studs to support the sides of the membrane.
Build the curb from three pressure-treated 2x4s.
Tack 3/4-inch guides around the perimeter (not necessary for stalls larger than 4 feet on both sides).
Cut a hole in the center of the floor for the lower drain plate.
Coat the bottom of the lower drain with beads of siliconeone outside and one inside the bolt circle.
Cut a section of metal lath to the same dimensions.
The metal gives the floor a “tooth” for the mortar.
Mix the mortar in a wheelbarrow (not a bucket).
Compact the mortar into an even surface and let it dry overnight.
Roll Out Membrane
Roll out the membrane on the surrounding floor.
If the stall is larger than the membrane, solvent-weld additional sections.
Let the primer dry.
Overlap the edges and roll them tightly.
After 5 minutes, make a run at separate the seam.
If it comes apart, repeat the process.
Working from the drain outward, smooth out the air bubbles.
Then staple the top 1 inch of the sheet to the blocking.
Weld the corners and cut the sheet at the bottom of the jambs.
Fold the sheet over the curb and tack it only on the front.
Solvent-weld a dam corner (available from the manufacturer) over the jamb cuts.
Then unscrew the bolts so you’re able to fasten the upper drain plate.
Don’t seal the underside of this plate with siliconeit will clog the weep holes.
Using a long sharp knife, carefully cut away the membrane in the drain hole.
(Don’t use a utility knife.
Its blade is not long enough to make a clean cut.)
Fold the corners into triangles and solvent-weld the folds in place.
Fill the pan with water to about an inch from the top of the membrane.
Then check the level.
If it’s still at the mark, the pan is watertight.
If the water is below the mark, the membrane has a leak somewhere.
Check the surrounding floor for water, which would have come from a leak in the side.
Tighten the bolts if they feel too loose.
To protect the strainer and drain from stray mortar and thinset, apply two layers of crisscrossed masking tape.
Overlap the tape and cut it flush around the edge of the strainer.
Attach Waterproofing Membrane
If any of the walls are outside walls, insulate them with fiberglass batts.
see to it you don’t put staples through the pan membrane lower than 1 inch from the top.
Cut and Fasten Backerboard
Clean off any grit with a damp cloth.
Cut backerboard to fit the walls and set it on 1/2-inch shims.
Remove the shims and caulk the space at the bottom with silicone.
Tape and mud the seams with modified thinset.
Spread Mortar and Lay Lath
Mark the slope on the walls.
Protect the weep holes from clogging and mix up another batch of dry mortar.
Work in sections, sloping the floor toward the drain.
Bend lath to fit the curb and pack it, slanting the top inward.
Protect Weep Holes
Weep holes allow moisture trapped in the mortar bed to escape down the drain.
If the moisture can’t go down, it will go upinto your grout, causing mold and mildew.
Mark the plane on the backerboard with a felt-tip pen.
Compute Slope
The floor of the pan must slope 1/4 inch for every linear foot.
Compute the amount of slope based on the dimensions of the enclosure and mark this point on the backerboard.
Press the tiles firmly into the mortar to double-check they conform to the slope of the floor.
