How to Install a Polystyrene Shower Base

Vacuum the interior subfloor of the shower area to remove dust. Pay special attention to the corners, which trap debris easily. Insert a rag into the center drain opening so that nothing falls down into it during the installation process.

Open a can of wood primer and apply a coat to wood subfloors, using a paint roller. Wait two hours or until the floor is completely dry to the touch. Primer is not required for other subfloor materials, such as concrete.

Measure the length and the width of the shower pan area, using a tape measure. Write down the measurements for later reference. Then take measurements from the rear wall and a side wall until you reach the drain hole opening, writing down these measurements, as well.

Lay the polystyrene shower base on a flat surface and measure the width and the length to determine if it requires cutting. If cutting is required, cut the base to size, using a jigsaw. When reducing the length or the width, divide the reduction amount in half and cut that amount off other sides. Do not cut the entire amount off of one side.

Refer to your measurement notes and use the tape measure to identify the drain location on the polystyrene shower base. Draw a circle in the area with the pencil and then cut along the line, using the jigsaw.

Spread a 1/4-inch layer of thinset mortar over the entire floor area of the shower, using a 1/4-inch notched trowel. Hold the trowel at a 30- to 40-degree angle to create grooves in the thinset.

Place the shower base into the mortar, ensuring the center opening centers over the drain. Press it down firmly and set a level on top. Push down on any high areas until the entire base levels.

Locate the plastic shower drain base and insert it into the center drain hole after removing the rag. Push down until it clicks into place. Then insert the remaining pieces of the drain supplied with the shower base. Typically, this consists of a rubber ring pushed into the hole, then a rubber dome, which also pushes into the hole.

Spread additional mortar around the outer edge of the base and extend it up each wall by 2 inches. Cut off strips of waterproofing tape and apply the strips over the mortar so that they overlap the seams completely.