How to Install a Three-Piece Shower

A fiberglass shower stall can be a quick fix for an old bathroom or an inexpensive alternative to constructing a stall from tile or stonework. Fiberglass stalls come in one- and three-piece units. One-piece units are bulky and hard to maneuver, requiring two people to install them. Three-piece units, however, can be transported and installed with comparative ease by one person. The three pieces consist of a base and two C-sections that fit on top. They usually clip together, and you have to seal the joints with special sealing tape. The tape should be provided with the stall.

Step 1 – Frame the stall enclosure with 2-by-4-inch studs. Nail the tops and bottoms of all studs with 16d framing nails. The stub-outs for the hot and cold water lines should extend up through the bottom plate of the back wall. Double-up the studs framing the shower opening, and plumb them with a level before nailing them. It’s important that they are perfectly straight.

Step 2 – Set studs on the sub-floor to reinforce the shower base. The configuration of these studs will depend on the design of the base and some bases are already reinforced. Use a level to make sure they are horizontal. Place shims between the reinforcements and the sub-floor where needed to make them level.

Step 3 – Turn the shower base over and cut a hole for the drain from the bottom, if one is not already pre-cut. Use a hole saw that is the same diameter as the threaded part of the drain assembly that will extend through it. Place the tip of the pilot drill bit on the lowest point of the base and then drill the hole.

Step 4 – Put the base temporarily in position and mark the position of the hole on the sub-floor. Drill through the sub-floor with a hole saw that is 1/2 an inch to 3/4 of an inch larger in diameter than the drain extension that will extend through it. This will give you room to make adjustments.

Step 5 – Stand the base on its side. Unscrew the drain assembly and insert the top part of the drain through the top of the shower base, then slide on the washers that came with the assembly and screw on the retaining nut. Tighten the nut with channel-locking pliers. Finally, screw the drain extension onto the threaded part of the drain that extends past the nut.

Step 6 – Set the base in position with the drain extending through the hole in the sub-floor and be sure it is sitting properly on the reinforcement framing. Make sure it is level, then attach it to the studs with drywall screws. The placement of the screws will depend on the design of the stall, but most stalls have flanges that extend up from the base through which you can drive them. On some models, the flange may extend around the studs framing the opening. If this is the case, screw these flanges to the studs.

Step 7 – Set the middle piece of the stall on top of the the bottom. Starting at the back corners, push it into the base until the two pieces snap together. Pry the joint slightly apart with a pry bar and remove the liner material, then seal the joint with seam tape that should be provided with the stall. Install the top piece of the stall in the same way.

Step 8 – Screw the flanges of the middle and top piece to the studs framing the opening with drywall screws.

Step 9 – Drill holes for the shower valve and the shower head from behind the stall. The sizes of these holes and their positions will depend on the plumbing fixtures you plan to install.

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