How to Use a Foam Insert for a Shower Pan

Sweep or vacuum the entire interior area of the shower base using a broom or a shop vac. Ensure that the interior surface of the floor is clean before installing the foam insert.

Apply wood primer to the entire floor using a paint roller if it consists of plywood. Wait until the primer dries for 24 hours before proceeding. If the subfloor is concrete, primer is not required.

Measure the width and the length of the shower floor using a tape measure. Lay the foam insert on the floor and measure it to determine if it requires cutting to fit. If cutting is required, determine how much length requires removal and divide the number by two. Remove that amount from both sides of the insert using a hand saw or a jigsaw. Repeat the process to trim the width.

Measure the location of the floor drain inside the shower and draw the location on top of the foam insert. Cut out the center drain hole using the jigsaw.

Open a tub of thinset mortar and scoop up 1 cup using a U-notched trowel. Spread the thinset over the entire base of the shower floor until it is 1/4-inch thick. Hold the trowel at a 45-degree angle as you spread the thinset to create ridges in the top.

Spread additional thinset along the bottom of the wall up to the height where the insert will cover.

Place the foam insert into the thinset and press it down to secure it. Lay a level on top of the panel to determine if it is even and press down any high areas until they are even.

Locate the shower drain base, which is a square rubber flange with the center circular hole. Insert it into the center drain hole until it fastens around the drainpipe. In some installations, you will hear a click. Insert the inner drain seal, which is a cylinder, into the drain base as far as possible.

Open a can of waterproofing sealer and apply it to all edges of the insert using a paintbrush. Apply additional sealant to other seams in the insert, for example if it has two sections.

Apply waterproofing tape along all edges of the foam insert so that half the tape is on the wall and half the tape is on the insert. If your foam insert has two pieces, seal any other seams with the tape as well.