How to Mortar a Shower Pan

Prepare the frame for the shower pan, if you haven't already. Create a curb for the shower by cutting, stacking and nailing down the desired number of 2-by-4s. Cut and install 2-by-10s between stud bays around the shower perimeter at the base.

Staple construction or building paper to the subfloor.

Glue the bottom piece of the three-piece shower drain into the drain opening using PVC cement and stuff a rag into the drain opening to block mortar from falling into the drain. Place the drain bolts into the drain holes but do not tighten them completely.

Calculate the required rise and mark this level on the wall. Measure the distance between the center of the drain and the center of the wall farthest from the drain. The pan should rise at least 1/4 inch for every 12 inches of this distance. Measure the length of the total required rise up from the point of the wall that is level with the drain and mark this new spot. Use a level to draw an even line around the perimeter at this height.

Cut metal lath to size, removing a space for the shower drain, and staple it to the floor.

Prepare thinset mortar so that it has a fairly dry consistency. Consider mixing in a polymer additive for increased strength.

Pack mortar into the lath. Use a trowel and build the mortar up so that it reflects the planned slope, reaching the line marked around the perimeter of the shower.

Check the mortar for slope and use a wooden float to smooth it. Hold a level or flat board to the drain with the other end at the line on the wall. Use the straight edge to check the mortar level, filling in any low spots and removing excess mortar. Work around the entire pan. Smooth the mortar with the wooden float and let the mortar dry for at least a day before continuing.

Place waterproof membrane over the mortar. Cut small slits for the bolts from the drain to fit through and make an opening for the drain hole. The membrane should be made to fit so that it will extend over the shower curb. Glue the membrane to the mortar using an adhesive appropriate for the material. Also, glue dam corners over the membrane where the curb meets the wall.

Attach the middle drain piece and the strainer. Remove the bolts from the lower piece, place the middle piece and re-install the bolts, tightening them to create a watertight seal. Place the strainer piece in the drain so that it is 1-1/2 inches above the shower pan.

Install cement board on the shower walls, if desired, using wood shims to create a 1/4-inch gap along the bottom of the wall.

Cut metal lath to fit the three sides of the curb and staple it to the curb.

Apply mortar to the curb. Pack the mortar into the lath, then use a board flush with the wall materials to guide a trowel to scrape off excess mortar.

Draw a reference line around the perimeter of the shower 1-1/2 inches above the shower pan.

Place mortar into the shower pan. Apply enough mortar so that it reaches about halfway to the reference line.

Embed metal lath in the mortar. Cut it to fit in the pan, leaving a 1/2-inch space around the drain.

Fill in the remainder of the mortar bed. Once the rough shape is reached, use a level and wooden float to check for slope and evenness and make corrections as needed. Smooth the surface with the float and let the mortar dry for at least a day before applying the tile layer.