Gelcoat cures anerobically. I'm sure you dom't know what that means, so I'll explain. When you put gelcoat in a mold to make a part, it never fully cures untill you lay up your fiberglass on top of it. The gelcoat hardens when it is no longer exposed to air. THAT IS WHY YOU BED FIBERGLASS IN IT. IT IS CHEMICALLY DESIGNED FOR THIS PURPOSE.