How to Seal a Fiberglass Bathtub

White bathtub in a bathroom with a checkerboard floor pattern
  • 4-24 hours
  • Beginner
  • 100-200
What You'll Need
Course grit and fine grit sandpaper
Marine-grade fiberglass filler
Fiberglass hardener
Mixing buckets
Putty knife
Gel coat
Stirring sticks
Small roller or paint brush
Respirator and eye protection
Rubber gloves

Fiberglass bathtubs are very durable and strong, but over years, they may become damaged from constant use. If a new tub is not in your budget, you can repair and reseal the exiting tub yourself. This project is fairly easy and inexpensive, and it creates great results. Follow these steps to seal the bathtub.


Fiberglass is just what it sounds like: it is made from very thin fibers of spun glass. It can be extremely damaging to your eyes and lungs, so wear a respirator and eye protection when working with it. Wear rubber gloves to prevent glass fibers and chemicals from irritating your skin.Open any windows and run the exhaust fan to help remove hazardous fumes.

Step 1 - Preparation

Fiberglass filler is available at most home improvement stores. If your local store doesn't carry it, you can also go to a marine supply shop.

Remove the faucet and drain hardware, if necessary. Use course grit sandpaper and the sander to smooth the cracks and scratches on the fiberglass surface. Once the sanding has been completed, remove any remaining dirt, dust, and debris with acetone and rags. Rinse well, as any leftover residue will prevent the fiberglass filler from adhering to the surface.

Step 2 - Applying the Fiberglass Filler

Pour the fiberglass filler and hardener into the empty bucket. Use the stir sticks to mix it to the proper consistency.

Apply the fiberglass mixture to the bathtub using the putty knife. Spread the mixture evenly over the affected areas and feather the edges to match the existing tub surface. Allow the fiberglass mixture to harden before continuing to the next step.

Step 3 - Applying the Gel Coat

Use fine grit sandpaper and the sander to smooth the repaired areas of the fiberglass bathtub. Use a damp rag to remove dust and a dry rag to remove moisture.

Add the gel coat and hardener to another empty bucket and mix it according to the manufacturer's directions. Once the mixture is at the recommended consistency, apply it to the fiberglass bathtub using either the paint roller or paint brush. The paint roller will create a smoother finish. Apply a second coat while the first coat is still sticky.

Step 4 - Sanding

Once you have finished repairing the fiberglass bathtub, lightly sand the surface with very fine grit sandpaper. Doing so will roughen the surface just enough to prevent slips when the tub is wet. Alternatively, you can apply non-slip appliqués to the floor of the tub to prevent falling.