How to Install a Fiberglass Shower Pan in an Existing Shower

Remove the existing shower floor. If the existing shower floor is made of tile, use a utility knife or chisel held at a 45-degree angle to the tile and hit the handle with a hammer to break the tile from its mortar bed. Continue down to the copper pan, loosen beneath the pan with the utility knife and pull it free. If the existing shower pan and walls are acrylic or fiberglass, remove the shower walls first by loosening them with a utility knife and pulling them free, then unscrew and remove the pan.

Remove the first few rows of tile above the shower floor in a tiled shower. Select a complete grout joint to make the reinstallation of tile easier, and break the tile away from the backerboard with the utility knife and hammer. Remove all mortar, but be careful not to harm or break the backerboard.

Prepare the surface of the shower floor to receive the shower pan. Use a 30-lb. roofing mat, or adhesive backer to even out any inconsistencies in the shower floor. This same roofing mat should also cover the bottom several inches of the shower walls to provide a watertight seal. If the manufacturer recommends support for the shower pan, create a crushed mortar bed of one part Portland cement to five parts damp sand, allowing it to dry and crushing it to the consistency of driveway stone and creating a layer beneath the shower pan for support.

Place the shower pan on the prepared shower floor, and line up the drains.

Install the shower drain. If the drain is provided with the fiberglass pan, follow the manufacturer's instructions. If using a separate drain, install the drain in two pieces by placing the interior first and screwing the top down into the shower pan.

Screw the shower pan directly into the wood studs of the shower walls to secure the pan in place.

Replace the fiberglass walls of the shower, or replace the missing rows of tile. Leave a 1/8-inch space between the tile and the top of the shower pan; do not fill this space with caulk. Fiberglass shower walls will come down over the top of the pan.