Before you start repairing your damaged fiberglass tub, prepare yourself for the job by putting a respirator and your safety goggles on.
Now grind directly over the damaged area removing broken pieces of fiberglass with hands, to form a groove in the bathtub. Carefully taper the edges of the groove you have just formed in the tub.
Wipe off the surface of the bathtub around the damage using a rag soaked in acetone or any other cleaning solvent.
Now put on your rubber gloves and combine the filler and catalyst in a small bowl, following the manufacturer’s instructions.
Use a putty knife or trowel to apply the filler to the groove in the bathtub.
Fill the groove with enough filler so it’s level with the surrounding fiberglass and smooth it out.
Let the filler dry and harden for at least a couple of hours and then sand it smooth using a palm sander.
After sanding the filler smooth, wipe it clean with a rag dipped in acetone.
Mix the hardener and gel coat together in a small bowl using a wooden or plastic stir stick. Follow the manufacturer’s direction to make the paste of gel coat and hardener.
Once the gel coat is thoroughly mixed, apply it in evenly to the surface of the filler with the help of a clean paint brush.
Once the filler surface has been covered completely, allow the gel coat to harden completely.
Apply another coat if needed and let it dry and harden for 20 to 24 hours before running the water into the bathtub.