How to Build a Shower Floor With Sit Down Benches

Build the frame for the shower pan. Remove any materials necessary to expose the subfloor. Measure the opening at the shower threshold where the curb will be placed, transfer this measurement to two-by-fours and cut three lengths of two-by-fours to this size. Stack the boards in the shower threshold and nail them to the wall studs and floor joists to form the curb. Measure the openings between the wall studs.

Measure, cut and staple a section of building paper to the subfloor. Cut a hole for the drain opening.

Glue the bottom section of a three-piece shower drain into the drain opening using PVC cement. Shove a rag into the drain opening to block loose mortar from accidentally falling into the drain.

Calculate and plan for the total rise that will be required in the pre-pan layer. Measure the distance between the center of the drain opening and the farthest wall and multiply this distance, in feet, by 1/4 to determine the total required rise in inches. Use a level to locate and mark the height of the drain opening on the wall. Measure up the distance of the total required rise and mark this height. Use the level to draw a line around the perimeter of the shower at this elevation.

Measure, cut and staple a section of metal lath to fit in the shower floor, leaving a 1/2-inch gap around the drain.

Prepare the mortar and pack it into the metal lath. Mix the mortar so that it has a fairly dry consistency and consider using a polymer additive to increase strength or other characteristics. Use a trowel to place the mortar on the shower floor and build it up so that it roughly reflects the slope between the wall and the drain.

Run a straightedge or level over the mortar with one end at the drain opening and the other at the line on the wall. Check for any low or high spots and add mortar and remove excess mortar as needed. Run a float over the surface to create a smooth finish.

Measure, cut and glue a section of waterproofing membrane to the shower pan, walls and curb. The membrane should be sized so that it will extend 8 inches up each wall and up and over the curb. Cut slits for the drain bolts, an opening for the drain hole and cut the membrane for the curb at the wall studs so that it fits over the curb snugly.

Complete the shower walls to the point that the bench can be built. Typically, this will involve installing plastic sheeting or a waterproofing membrane against the studs, then placing cement backerboard over the waterproof layer.

Plan and prepare the blocks for the bench. Lay out the blocks as they will be placed in the mortar and break them up as needed to accommodate the planned design. If the bench will be against a wall, only the faces need be constructed from solid block; the space between the faces of the bench and the wall can be filled in with rubble and mortar.

Moisten the cement backerboard walls wherever the mortar will be in contact with the wall using a damp sponge.

Spread about 1 inch of mortar on the shower floor where the bench will be built.

Place the first course of blocks in the mortar. Set the first block, wiggling it gently as it is placed to release any air bubbles. Use a level to ensure that the block is even and make any necessary adjustments. Place subsequent blocks until the first course is completed, buttering the end of each block before it is placed next to another and checking frequently to ensure that the blocks are level and each face is even.

Place the second and any subsequent courses of blocks. Spread mortar on the existing course, then lay the blocks using the same techniques as with the first row.

Fill in any space between the faces of the bench and the wall with rubble and mortar, building it up nearly to the top of the blocks.

Shape the top of the bench. The bench top should have a slight slope to facilitate efficient drainage. Build up mortar to reflect this slight slope, then run a straightedge over the mortar to check for low or high spots and move the mortar around as needed. Run the level over the top of the seat to ensure there is a slight slope.

Mortar the faces of the bench. Although the block faces were checked for evenness throughout the stacking and mortaring process, they are likely not perfectly even. To account for this, spread a thin layer of mortar over the side of each bench, then run a straightedge over each face to create an even surface.

Install the middle and top drain pieces. Use drain bolts to secure the middle drain piece to the bottom piece, tightening them to create a watertight seal. Adjust the height of the top drain piece, or strainer, to reflect the planned depth of the mortar bed.

Measure the distance of the planned mortar bed depth up the wall and mark this height. Use the level to draw a line around the shower perimeter at this height.

Place enough mortar in the shower pan to make up about half of the planned mortar bed depth.

Press a section of metal lath cut to fit in the shower pan and around the drain into the mortar.

Build up the remainder of the shower mortar bed. Pack the mortar in between the line drawn on the wall and the drain. Use the straightedge to locate any low or high areas in the mortar. Finally, run the float over the mortar surface to create a smooth finish. Let the mortar cure for at least a day before installing the desired surfacing.