How to Reinforce a Shower Mortar Bed

Prepare the shower pan so it is ready to receive the lath and mortar for the pre-pan layer. Expose the subfloor and stud walls, staple building, tar or felt paper to the subfloor and glue the bottom portion of a three-piece shower drain into the drain opening. Stuff a rag into the drain opening to protect it from mortar.

Staple galvanized metal lath or wire mesh to the subfloor. Cut a hole to accommodate the drain, leaving 1/2 inch of space around the drain.

Prepare the mortar for this pre-pan level. Mix a thinset mortar so that it has a fairly dry consistency and include a latex additive to improve strength. This layer of the shower pan establishes the slope for the remainder of the shower pan, so a rise in elevation of at least 1/4 inch per foot of distance from the drain to the center of the farthest wall must be taken into account. The best way to do this is to calculate the required rise and draw a level line around the perimeter of the shower that the mortar bed must reach.

Pack mortar into the metal lath with a trowel and build it up to the line on the wall. Use a level and float to make sure that the mortar is smooth and properly sloped. Let this pre-pan mortar sit for at least a day before continuing.

Prepare the shower pan for the next layer of mortar, the actual mortar bed. Attach a waterproof membrane to the underlying mortar using an adhesive suitable for the material type. Attach the second and third drain pieces to the drain, adjusting the drain so that the strainer is at least 1 1/2 inches above the pan. Measure up the same distance on the shower wall and draw a line around the shower perimeter at this level.

Mix and place mortar on the pan, building it up to about half of the planned 1 1/2-inch height.

Place metal lath on this mortar. It must be cut to cover the pan fit around the drain.

Pack mortar onto the pan to complete the mortar bed. Work to the level of the line on the wall and use a wooden float and level to recognize and make any necessary adjustments. Let this mortar cure for at least several hours, depending on the mortar and additives used, before applying tiling.