Fiberglass is a durable material that is used in many marine applications, such as pools, hot tubs, showers, boats and many more. Even though fiberglass is strong, it's still susceptible to crack or fail after years of wear and tear. A good characteristic of fiberglass is its capability to be repaired no matter what the damage is. Fiberglass is relatively easy to work with and is fairly cheap, depending on the size of the repair. All fiberglass supplies can be found at your local marine supply store.
Determine where the damage is. Wearing a respirator, sand the entire damaged area using 80 grit sandpaper. If it's a deep crack, sand the walls of the crack down to a gradual taper. The more gradual the taper is, the better. Also scuff all the way around the crack or fracture an extra 2 to 3 inches.
Clean the areas that are being repaired using a rag and acetone. Wipe away any dust or other debris that is on the surface of the repairs.
Mix the fiberglass filler with the hardener using a small bucket and a stir stick. Follow the recommendations on the container for the correct amount of hardener. Apply the filler to the cracks using a putty knife. Smooth the filler out so it's flat and level with the surrounding fiberglass. Let the filler cure until it's completely hard.
Put on a respirator and sand the filler using a palm sander and 200 grit sandpaper. Sand the filler until it blends in with the surrounding fiberglass.
Tape the perimeter of the repaired areas using painter's tape. Mix the matched fiberglass gel coat with the hardener as directed on the containers. Use a small bucket and a stir stick to thoroughly stir the gel coat.
Apply the fiberglass gel coat to the repaired areas using a felt roller. Let the gel coat cure for at least 24 hours before it gets any water on it.