How to Install a Fiberglass Tub and Surround

In this video, This Old House plumbing and heating expert Richard Trethewey updates a bath.

Steps for Installing a Fiberglass Tub:

1. Screw a 2×4 ledger board across the rear wall to support the new tub.
2. If necessary, replace the shower valve while the wall framing is still exposed.
3. Attach the drain and overflow pipe to the tub prior to installing the tub.
4. Apply plumber’s putty around the threaded portion of the strainer.
5. Press the strainer into the drain hole in the tub. Place a rubber gasket over the strainer on the backside of the tub.
6. Thread the strainer into the drainpipe and tighten with pliers. Remove the excess putty that squeezes out from under the strainer.
7. Install the trip lever from inside the tub. Fasten the overflow plate to the tub with two screws.
8. Carefully set tub into place against the wall studs.
9. Predrill 3/16-inch-diameter screw holes through the tub’s flange, then fasten the tub to the wall studs with 1¼-inch-long decking screws.
10. Use a drill and hole saw to cut holes through the fiberglass tub surround for the shower valve and tub spout.
11. Stand the fiberglass surround on top of the tub. Slip 2-inch-wide wood blocks under the surround to temporarily raise it above the tub.
12. Apply a continuous bead of silicone caulk around the upper edge of the tub.
13. Remove the wood blocks and set the surround down onto the tub.
14. Predrill 3/16-inch-diameter screw holes through the surround’s flange, then fasten the surround to the studs with 1¼-inch-long decking screws.
15. Solder together a threaded copper piece to connect the tub spout to the threaded water-supply fitting inside the wall.
16. Tighten tub spout to shower wall, and then screw the chrome-plated strainer to the tub drain.
17. Fill the spaces above the tub surround with moisture-resistant drywall. Fasten the drywall strips to the studs with 1¼-inch-long decking screws.
18. Conceal the seams in the drywall with joint compound and drywall tape.
19. After finishing the drywall, prime and paint the walls with mildew-resistant paint.
20. From below the tub, use pliers to tighten the trap to the tub drain.

Tools: