Typically, gelcoat isn't recommended over epoxy because they’re chemically incompatible and the gelcoat won't adhere properly.
However, for relatively small cosmetic repairs, epoxy resin can be used in the repair layup if you do the following:
- Measure the epoxy and hardener accurately, mix properly, and apply as directed.
- Allow it to cure completely.
- Use a Scotch-Brite™ pad and water (do not use solvent) to remove any amine blush completely, then allow the repair to dry completely.
- Prepare the surface properly, according to the gelcoat manufacturer’s directions.
- After sanding and fairing clean very well with acetone.
- Apply the gelcoat finish beyond the edges of the repair area.
This video shows you how to do small, non-structural epoxy repairs finished with gelcoat.