How to: Custom Shower Pan

Prepare the site for the shower pan. Remove any materials necessary to expose the subfloor. Cut three lengths of 2 x 4 to fit at the shower threshold and nail them to floor joists and wall studs to form the curb. Fit 2 x 10s into stud bays to form a wall around the base of the shower.

Measure and cut building, felt or tar paper to fit the subfloor within the pan and staple it to the subfloor.

Install the bottom piece of the three-piece shower. Cut a hole in the building paper and glue the piece into the drain opening using PVC cement. Stuff a rag into the drain to block any mortar that could accidentally fall into the drain.

Calculate and mark the total required rise that the shower floor must exhibit to force drainage. The minimum required slope is 1/4 inch per every foot of horizontal distance. Measure the total distance between the center of the shower drain and the farthest wall and apply the minimum slope to this distance. Measure this distance up the wall, mark the spot and use a level to create a line at this height around the shower walls.

Measure and cut metal lath to fit and staple it to the floor. Cut an opening for the drain, leaving 1/2 inch of space around the drain.

Prepare mortar for the pre-pan. Mix a thinset mortar to have a fairly dry consistency and consider using a polymer additive to increase mortar strength.

Create the mortar prepan. Pack mortar into the metal lath and build it up to reflect the planned slope. Once the rough shape has been achieved use a level or other straight-edge to finalize the slope. Hold the level so one end is at the drain and the other end is on the line drawn on the wall. Move the level around the perimeter, identifying and correcting any low or high spots. Use a wood float to smooth the surface. Let the mortar cure for at least a day before continuing.

Measure and cut waterproof membrane to fit the shower pan. Cut the membrane so several inches of membrane extend up the shower walls and up and over the curb. Cut small slits for each of the drain bolts and an opening for the drain.

Glue the waterproof membrane to the underlying surface using an adhesive suited for the specific membrane material.

Attach the middle drain piece to the portion of the drain that has been glued into the drain opening. Remove the rag from the drain opening. Place the middle drain piece atop the bottom piece, align the bolt holes and install the drain bolts. Tighten the drain bolts to create a watertight seal.

Prepare to create the mortar bed. Attach the top drain piece, the strainer, and adjust its height to reflect the planned mortar bed depth. The mortar bed should be at least 1 1/2 inches thick. Measure up the wall, mark the height the bed should reach and draw a level line around the shower perimeter. Prepare the mortar for this layer

Place enough mortar in the shower to make up about half of the planned mortar bed thickness.

Cut and place metal lath on top of the mortar.

Mortar the remainder of the bed. Create the rough shape of the bed before using a level to identify and correct any unevenness.

Finish the shower pan, curb and walls as desired. In many situations, tiling is the preferred finish. Lay the tiles for the floor in a thin layer of mortar, then attach metal lath to the curb, create a mortar bed and place tiles that have been cut to fit the curb. Once the tiles have been placed throughout the shower the entire unit should be grouted, cleaned and sealed -- and all joints or openings treated with silicone caulk.