How to Build a Shower Base With a Seat

Build the frame for the shower pan. Measure the opening at the threshold where the curb will be placed, cut three sections of 2-by-4 to this length, stack the boards in the threshold and attach them to floor joists and wall studs using 16d galvanized nails. Measure the openings between studs around the shower, cut sections of 2-by-10s to fit the openings and install the 2-by-10s in the stud bays to form a low wall around the shower pan.

Staple a section of building or felt paper to the subfloor within the shower, cutting it to fit within the area and making a hole to accommodate the drain opening.

Glue the bottom piece of the three-piece shower drain into the drain opening using PVC cement. Stuff a rag into the drain opening to keep loose mortar from accidentally entering the drain.

Determine the total rise that will be required on the shower floor and plan for the establishment of the slope. Measure the distance, in feet, between the drain opening and the farthest wall and multiply this number by 1/4 to determine, in inches, the total rise required. Use a level to mark the height of the drain piece on the wall, then measure up the distance of the required rise. Mark this new point and use a level to draw a line around the shower perimeter at this elevation.

Cut a section of metal lath to fit the floor of the shower, leaving a 1/2-inch gap around the drain flange, and staple the lath to the subfloor.

Prepare mortar for the pre-pan layer. Mix thinset mortar so that it has a fairly dry consistency. Use a polymer admixture to improve strength.

Pack the mortar into the metal lath, building it up to roughly reflect the slope between the line on the wall and the drain opening. Run a straightedge or level over the mortar, placing one end at the drain and the other at the wall, checking for and correcting any low or high spots. Float the surface of the mortar to create a smooth finish. Let the mortar cure for about a day before continuing.

Measure, cut and adhere a section of waterproofing membrane to the shower floor. The membrane should be cut so that it will extend at least 8 inches up each wall and up and over the curb at the threshold. Cut a small slit to accommodate each drain bolt and an opening for the drain hole. Cut the membrane at the wall studs so that it fits over the curb easily. Glue the membrane to the underlying material using an adhesive suited for use with the specific membrane material. The membrane can be stapled to the wood for additional security but place staples only above the level of the curb and on the top and outer faces of the curb.

Glue dam corners into the interior corners of the curb to provide additional reinforcement.

Complete the shower walls up to the point that they are ready to be finished. This typically involves attaching a moisture barrier to the studs followed by cement backerboard.

Plan and lay out the cinder blocks or bricks for the faces of the seat. There can be a space between the row of blocks at the faces of the seat; this space can be filled in later with pieces of block and mortar. Break up cinder blocks as needed to accommodate the seat design.

Spread about an inch of mortar on the floor of the shower where the seat will be built. The same type of mortar that was used for the shower pre-pan can be used here.

Moisten the cement backerboard walls where the mortar will be in contact with the walls. This will keep the board from absorbing moisture from the mortar and impairing setting.

Set the cinder blocks for the first course, or layer, in the mortar. Wiggle each gently as it is set to release air bubbles, check for evenness with a level and butter the end of the next block before setting it next to the adjacent block or wall. Once all of the blocks or sections of block for the first row have been placed, check each face of the seat to make sure the tops are level and the fronts even.

Continue building up the seat one course at a time until you reach the desired height. Use the same mortaring and setting techniques as for the first coarse, making sure that the tops of the blocks are level and the faces as even as possible.

Fill in the center of the seat between the built-up faces and the wall if there is a gap. Build up the center with pieces of rubble and mortar so that it is roughly even with the tops of the blocks or bricks.

Form the top of the seat. The seat surface should slant toward the drain slightly to force drainage. Build up the mortar to reflect this slight slope and run a straightedge over the surface to check for and correct low and high spots. Use a level to check for slope.

Mortar the faces of the seat to fill in any imperfections, ensure that mortar is packed well between the blocks and that the surface is totally even and smooth. Place a thin layer of mortar on each face and use a straightedge and level to make sure the surface is smooth and even.

Plan for and begin to build up the mortar bed. Install the middle and top pieces of the drain, tightening the drain bolts with a socket wrench to create a watertight seal. Adjust the height of the drain strainer to reflect the planned depth of the mortar bed. Mark the planned height on the walls and draw a line around the shower perimeter at this level. Place enough mortar in the pan so that it is built up to about half of its thickness.

Cut a section of metal lath to fit within the shower pan, again leaving a space around the drain, and press the lath into the mortar.

Build up the remainder of the mortar bed. It should maintain the slope that was established in the pre-pan layer. Once the mortar has been built up between the drain and the line drawn on the wall, run the straightedge over the mortar and make any corrections necessary.

Finish the shower floor, seat and walls as desired once the mortar has cured adequately.