Installing the Mud Layer

Instead of using cement board on the threshold, pre-form a sleeve of galvanized expanded metal by bending it over 2x4s. Pinch the legs of the metal in slightly so that the folded metal grabs the threshold.

Hold the wire 1 1/2 inches off the bottom of the shower pan, with the factory edge (without sharp edges that could puncture the membrane) on the inside of the pan.

After slipping the mesh over the threshold, nail it from the outside only to hold it in place.

Coat the expanded metal with thinset to finish prepping the threshold.

To keep the weep holes in the drain clear, spread a small amount of pea stone around the base of the drain.

Dump several buckets of dry-pack mortar (the same mix that was used to create the sloped layer) onto the membrane.

Pack the mortar tight to the membrane, especially in the corners, along the perimeter of the shower, and around the drain. Smooth the mixture using a wood float and a steel floating trowel.

Be sure the corners of the steel trowel are rounded to keep them from damaging the membrane.

Screed the final surface perfectly flat with no voids. For this step, a level works well to make sure that the surface of the mud base is sloped at around 1/4 inch per foot toward the drain.

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