Gel coat consists of polyester resin that's pigmented to match any color needed. Gel coat is used on fiberglass applications such as boats, hot tubs, showers and pools. Gel coat is a very strong substance that acts as paint as well as a protective layer. For outdoor applications, gel coat also can have additives that protect against UV rays. Gel coat is very thick compared to other paints and has to be sprayed using a special gel coat gun. Gel coat also requires a hardener to cure, which the gel coat gun automatically mixes with the paint while you are spraying. The spray guns can be found at your local marine supply store.
Prepare the surface you are spraying by scuffing the entire area using a fine grit sandpaper. The gel coat will not adhere to finished fiberglass unless it is scuffed because it has wax in it. Be sure to get in every crack and crevice that will be sprayed.
Remove all dust and grease left on the surface using a rag and acetone. It is important to be thorough with this step for the best results. Any grease spots can potentially cause a bubble to form in the finished gel coat, and the dust will show up in the gel coat to cause a rough finish.
Tape off any parts with masking tape that you do not want to have sprayed. If you need to cover large areas use cardboard and tape it in place.
Plug the gel coat gun into the air compressor and spray the first of two coats. Apply the gel coat starting from the top and working your way down. Overlap each pass by about an inch. Do not try to spray it on thick for the first coat--just a heavy mist. Once the first coat is sprayed let it cure until it starts to get tacky.
Apply the second coat, making sure to solidly cover the entire surface. Use the same technique as in the first coat, starting from the top and working your way down, overlapping each pass. Be sure to apply as evenly as possible for the best finish. Let cure until it is hard and cool to the touch.
Clean off the gel coat gun using acetone. If the gel coat is not cleaned off it will harden in the tip of the gun and possibly ruin it.
