Quote Originally Posted by rangerbobber View Post
Gee, that makes it a lot clearer.......... Bazinga!
LOL
It's a polyester based coating made from basically the same stuff ( polyester resin ) the rest of the boat is made from, only with pigments added to get color. they add thickening agents so it will stay on vertical surfaces when sprayed.

Gelcoat and polyester resins are cured by adding a catalyst, usually MEKP, Methyl Ethyl Ketone Peroxide which is an organic acid like material.
The catalyst increases the speed of a chemical reaction that causes the molecules in the resin or gelcoat mix to link together in a chain and change from a liquid to a solid.
When mixing resin or gelcoat with catalyst, you just have to add enough catalyst to get the reaction rate to speed up to a reasonable cure rate, but not so much catalyst that it creates extra heat in the reaction. ( the exothermic reaction )
Too much catalyst will get the resin or gel to cure fast and hot, but there is a possibility it will make the gelcoat shrink and pull away from the mold or repair.
Too fast a cure can also result in a weaker physical property for the glass part , as the faster cure rate develops shorter chemical chains, longer cure rates develop longer chemical chains which are more apt to be stronger.
Here are times in a fiberglass job shop ( not boats ) where you need a hot mix of resin to make a part or repair where the physical strength doesn't matter, you can add enough MEKP get the catalytic reaction going fast, where the resin will cure in minutes and also generate enough heat to catch the bucket of resin on fire when you are done..