How to Build a Waterproof Shower Pan

Prepare the base for the shower pan. Remove any materials necessary to the expose the subfloor. Cut, stack and nail two or three two-by-fours to the joists and studs at the shower threshold to create a curb. Cut pieces of two-by-tens and install them in the stud bays around the perimeter of the floor.

Cut construction paper to fit the shower base and staple it to the floor. Cut a hole in the paper for the drain opening.

Glue the bottom drain piece into the drain opening with PVC cement. Stuff a rag into the drain opening temporarily to keep any loose mortar from falling in.

Prepare to create the mortar pre-pan -- the layer in which slope is established. Measure the distance between the drain and the farthest wall, then plan for a rise of 1/4-inch per foot. Measure the height of this increase on the wall and draw a line around the shower perimeter at this level.

Cut metal lath to fit the bottom of the base, creating a hole to accommodate the drain and staple or nail it down.

Mortar the pre-pan. Use a trowel to pack mortar into the metal lath and roughly create the slope. Use a level to identify any unevenness and add or remove mortar as needed. Smooth the surface of the mortar with a wooden float and let it cure for at least a day before continuing.

Measure and cut waterproof membrane to fit the shower. The membrane should be cut to extend at least 8 inches up each of the shower walls and up and over the shower curb.

Cut small slits in the membrane to accommodate the bolts for the drain and cut an opening for the drain hole. Attach the second drain piece with the bolts, tightening the bolts to create a watertight seal.

Attach the membrane to the underlying mortar and wood using an adhesive suitable for the membrane material. The membrane can be stapled to the wood, but staples should only be driven through the material near the top of the wall membrane and on the top and outer side of the curb.

Glue dam corners into the corners created by the shower curb.

Continue constructing the shower pan. Attach the drain strainer and adjust the height of the drain to reflect the planned mortar bed thickness. Apply the mortar with uniform thickness to maintain the slope established in the pre-pan layer. Let the mortar bed cure and lay tiles or other surfacing materials.

Apply a sealant to the shower pan once the surface material has been placed, if the surface material can be penetrated by water. Otherwise, apply grout to the spaces between tiles and place a bead of silicone caulk along all joints within the shower.