Gelcoat is polyester rather than epoxy. Although epoxy will adhere well to polyester, the reverse is not true. Gelcoat is harder, thicker and heavier than varnish, but adhesion and repair are big problems. Another issue is that pure gelcoat will not cure in the presence of air. Inside a female mold it doesn't matter, but for ambient application waxy additives are mixed in that float to the surface and isolate the film from air during cure. Compare to epoxy blush.

Epoxy is stronger, more waterproof, more adhesive, and more expensive. IMHO polyester is a giant step backward, as the problems outweigh any advantages.

: Good morning america...
: I´m reading Hanson´s excellent book SEA KAJAK TOURING, X-mas present, and
: come across the term gel coat finish on fiberglas kajaks.
: What exactly is this gelcoat and can you use it on the conventional epoxi
: finish of a S&G kajak. Is is better than varnish?
: Thanks Joaquin