How to Build Shower Thresholds

Plan where the threshold, or curb, will be located and measure this space. If possible, locate the threshold so that it aligns with wall studs and floor joists.

Transfer the measurements for the curb to 2-by-4s. The curb will be three 2-by-4s high, so plan for three lengths of 2-by-4 for the curb. Curbs that will consist of two or more sides will require three lengths of 2-by-4 for each side.

Cut the 2-by-4s to the desired size.

Stack the 2-by-4s in the shower threshold, and attach them to the floor joists and wall studs with 16d galvanized nails.

Construct the shower pre-pan to a point that allows work to continue on the threshold. Place felt paper, the bottom piece of the shower drain, metal lath and a mortar layer that creates the slope inside the shower, and let the mortar cure adequately before proceeding.

Measure the shower pan area and curb, and transfer these measurements to a waterproof membrane made of CPE, PVC or another suitable material. The membrane must be sized so that it extends 8 inches up each wall, and up and over the curb. Cut the membrane for the curb at the wall studs so it fits over the curb neatly.

Adhere the waterproof membrane to the underlying mortar and wood using an adhesive suited for the specific membrane type. Glue the membrane down, working from the drain outwards. Staple the membrane along its upper edge, keeping all staples above the level of the curb. Staple the membrane to the curb only on the top and outside of the curb.

Affix dam corners to the interior corners of the curb to provide additional reinforcement.

Complete the shower pan on the inside of the threshold. Install the middle and top pieces of the shower drain, build up the mortar bed with embedded metal lath, and tile or otherwise finish the surface of the shower floor.

Measure and cut metal lath to fit up and over the curb. Bend it to fit snugly and staple it to the curb only on the outside and top of the curb.

Set a thin board, such as a 1-by-4, on top of the curb to serve as a guide for mortaring each side of the curb.

Pack mortar into the metal lath on the outside of the curb using a trowel. Once the mortar has been built up roughly, hold a level or straightedge to the mortar to identify any low or high spots and make adjustments to the mortar as needed. Run a float over the even mortar to smooth the surface. Repeat this mortaring process on the other side of the curb and let the mortar cure adequately before proceeding.

Complete the threshold as desired. To make a tiled surface, spread a thin layer of mortar over the existing mortar on the sides of the curb using a notched trowel and press tiles cut to the correct height into this mortar. Tiles should extend slightly over the top of the existing curb surface, and the tile for the outside should be barely taller than the interior tiles so that water will drain into the shower. Pack mortar into the top of the curb and cover it with bullnose cap tiles. Finally, grout the tiles and run a bead of silicone caulk around all corners within the shower.