Fiberglass is coated with a smooth layer of gel coat. Gel coat helps keep the fiberglass water-resistant and it smooths out the sometimes abrasive fiberglass surface. All fiberglass swimming pools have a gel coat surface. Over time, however, this gel coat will wear down and you'll need to replace it. If your swimming pool is small you can tackle this job on your own but consider hiring a professional if your pool is large. Give yourself several days to complete the job and look at the weather forecast to help ensure that there will be no rain while you are working.
Drain the pool.
Scrub the pool with a pool-cleaning solution and a pool brush. Rinse the pool completely and drain it.
Sand the entire pool with 240-grit sandpaper. This will remove almost all of the chipped and broken gel coat. It will also roughen the surface so that the new gel coat will adhere to it.
Rub the entire pool with a cloth soaked in acetone. The acetone will help ensure that there is no sawdust residue, dirt or other debris.
Let it dry for at least 24 hours. Never apply gel coat to a wet fiberglass surface.
Apply painter's tape to the areas of the pool that you don't want covered in gel coat.
Mix the gel coat with the catalyst that comes from the manufacturer with it according to packaging instructions. Mix just enough for one layer of gel coat. Once the gel coat is mixed with the catalyst you will have a limited time to use it before it dries and becomes impossible to use. This time limit will differ depending on the brand.
Pour the gel coat into the tank of a spray gun and turn the spray gun on.
Lightly spray the entire surface of the pool. Constantly move the spray gun as you are spraying to ensure that you don't apply too much gel coat to any one area. Spray a very thin layer for consistency and an even tone. Be aware that you will be giving the pool three even coats.
Let the pool dry for several hours.
Mix another batch of gel coat and spray the pool in the same manner. Let the pool dry and repeat the process once more. Let the gel coat dry for several hours.
Wet the surface with clear water.
Sand the gel coat with super-fine 1200-grit wet/dry sandpaper. This will help the fiberglass surface shine and will remove the tacky layer of the gel coat.
Refill the pool after the you've let it sit for at least three days. This will give the gel coat enough time to harden.