When Gelcoat is sprayed on at the factory it is 20,000 of an inch thick, any more than this and it will "Bog your boat down". Before you sprayed your gelcoat on did you happen to wipe the area in question down with any thing.Because the grey stuff your going over is more than likely some bottom antifouling paint and if you used some sort of reducer to clean it, you could of inadvertantly activated this coating. Bob G.