How to Apply a Mortar to Shower Stall Bases

Measure and cut a base for the mortar out of 3/4-inch plywood. Cut a hole into the plywood for the drain, using a jigsaw.

Nail the plywood to the subfloor where the shower is being installed.

Construct the sides of the form for the mortar by nailing a 2-by-10-inch board to the bottom of the studs where the walls will be and three 2-by-4-inch boards where the door will be. Stand the 2-by-10-inch boards on edge when installing them and lay the 2-by-4-inch boards flat, stacking them on top of each other.

Cut a piece of roofing felt to fit over the plywood, then lay it on top of the plywood, stapling it to the board.

Cut a piece of mesh to fit over the plywood, then lay it on top of the roofing felt, stapling it to the board. Cut a hole in the felt and mesh over the drain hole with a utility knife.

Insert the bottom flange of the drain assembly into the hole for the drain.

Prepare a batch of mortar, following the instructions on the packaging.

Spread the mortar on top of the plywood base. Place more mortar near the edges of the plywood, with less toward the drain hole.

Screed, or smooth, the surface of the mortar with a 2-by-4-inch board. Slope the mortar so that the mortar is about 1 1/2 inches higher around the edges of the shower than around the drain hole. Allow the mortar to cure for at least four or five days.