How To Install a Fiberglass Tub and Surround

*Cost information in this article sourced from Angi.

Installing a fiberglass tub and surround can refresh your bathroom and provide a durable, low-maintenance solution. This project requires careful planning and execution, but homeowners with intermediate DIY skills can complete it. We will take you through the process, from preparation to final touches.

In the video above, This Old House plumbing and heating expert Richard Trethewey demonstrates the installation process, providing valuable insights throughout.

Prepare for Installation

You’ll need to perform some prework before installing your new tub, including gathering supplies and removing the old tub. 

Materials

• Fiberglass tub and surround kit
• 2×4 lumber for ledger board
• Decking screws (1 1/4-inch long)
• Joint compound and drywall tape
• Mildew-resistant paint
• Moisture-resistant drywall
• Plumber’s putty
• Silicone caulk

Tools

• Caulk gun
• Drill/driver with 3/16-inch bit and hole saw attachments
• Pliers
• Propane torch (for plumbing connections)
• Screwdriver

Remove the Old Tub and Surround

Before installing the new tub and surround, you’ll need to remove the existing fixtures:

1. Carefully extracting the old tub and surround
2. Disconnecting the drain and overflow
3. Removing any surrounding tiles or panels
4. Shutting off the water supply

Be cautious of any hidden damage or mold behind the old fixtures, and address these issues before proceeding with the installation.

Install the Tub

Below are the steps to begin your tub installation.

Step 1: Set the Ledger Board

This board keeps the tub level and provides it with structural support:

1. Measure and mark the height of the ledger board along the back wall.
2. Cut a 2×4 to fit the width of the alcove.
3. Securely screw the ledger board into the wall studs.

Step 2: Attach the Drain and Overflow

Before placing the tub, you’ll need to attach the drain and overflow assembly:

1. Attach the drain and overflow pipe to the tub
2. Apply plumber’s putty around the threaded portion of the strainer.
3. Press the strainer into the drain hole in the tub. Place a rubber gasket over the strainer on the backside of the tub.
4. Thread the strainer into the drainpipe and tighten it with pliers. 
5. Remove the excess putty that squeezes out from under the strainer.
6. Install the trip lever from inside the tub. 
7. Fasten the overflow plate to the tub with two screws.

Step 3: Place and Secure the Tub

With the drain assembly in place, it’s time to set the tub:

1. Carefully lift the tub and place it into the alcove, resting it on the ledger board.
2. Check for level in all directions, shimming if necessary.
3. Predrill 3/16-inch holes through the tub’s flange.
4. Secure the tub to the wall studs using 1 1/4-inch decking screws.
5. Make sure the tub is firmly in place before moving on to the surround installation.

Install the Surround

The surround provides a finished look and protects the walls from water damage.

Step 1: Prepare the Surround

Before installing the surround:

1. Dry-fit the surround to ensure proper alignment and fit.
2. Measure and mark the locations for the shower valve and tub spout.
3. Use a drill and hole saw to cut holes through the fiberglass tub surround for the shower valve and tub spout.

Step 2: Apply Adhesive and Set the Surround

To install the surround:

1. Stand the fiberglass surround on top of the tub. 
2. Slip 2-inch-wide wood blocks under the surround to temporarily raise it above the tub.
3. Apply a continuous bead of silicone caulk around the upper edge of the tub.
4. Remove the wood blocks and set the surround down onto the tub.
5. Predrill 3/16-inch-diameter screw holes through the surround’s flange, then fasten the surround to the studs with 1 1/4-inch-long decking screws.

Finishing Touches

Complete the following steps to make sure your new tub and surround look polished and function properly.

Installing Fixtures

With the surround in place, you can now install the shower valve and tub spout:

1. Attach any additional fixtures, such as a showerhead or handheld sprayer.
2. Connect the shower valve, following manufacturer instructions.
3. Solder together a threaded copper piece to connect the tub spout to the threaded water-supply fitting inside the wall.
4. Tighten the tub spout to the shower wall, and then screw the chrome-plated strainer to the tub drain.

Complete the Walls

To finish the surrounding area, use these steps:

1. Apply mildew-resistant paint to protect against moisture.
2. Fill the spaces above the tub surround with moisture-resistant drywall. 
3. Fasten the drywall strips to the studs with 1¼-inch-long decking screws.
4. Sand and prime the walls.
5. Tape and mud the drywall seams.

Seal and Caulk

Properly seal and caulk your new tub to prevent leaks:

1. Apply silicone caulk along all seams where the surround meets the tub.
2. Allow the caulk to cure fully before using the shower.
3. Caulk around any fixtures and along the top edge of the surround.

Connect and Test the Plumbing

To complete the drain installation, connect the P-trap to the drain pipe from beneath the tub. Next, use pliers to tighten all connections securely.

Turn on the water supply and check all plumbing connections for any issues. Inspect the shower valve and tub spout for leaks, and run water through the shower and tub faucet to ensure proper flow and drainage. Test the overflow by filling the tub past the overflow point to confirm everything functions correctly.

Tools: