Yes, TotalBoat Gelcoat can be applied over TotalBoat Polyester Fairing Compound. TotalBoat Polyester Fairing Compound is an air-cure product, so the surface must be properly prepared before applying gelcoat.

To prepare the surface, clean it with acetone, sand with 80-grit sandpaper, and remove the sanding residue with a lint-free rag wetted with acetone. Allow the surface to dry completely before applying the gelcoat.