How flexible is gel coat?

I'm fairly experienced with fiber-glassing but have only used gelcoat once when I made a large hard-top for my catamaran. I now want to make a lazy bag for my mainsail. I'm going to make a mold and use divinycel foam for structural strength. The thing is, I want to keep the weight down so the glassing will be fairly thin, maybe just a couple of layers of biaxial cloth with polyester resin. So, if I have a gelcoat outer surface, will the gelcoat withstand the slight flexing that will undoubtedly occur when the sail is raised and lowered? ...or am I better off painting it?

 

That's asking quite a bit of it. Gelcoat can take periodic flexing but regularly bending it is just asking for it to craze with cracks.

 

I have no idea what a "lazy bag" is, but if you are using foam sandwich, the stiffness of it will pretty well guarantee minimal flex. But unless you are using a female mould and putting the gelcoat against that as the first stage of the lay-up, I don't see you would want to use gelcoat at all, paint would do. Gelcoat is also much more likely to crack if too thick, thinner gelcoat is more flexible.

 

Thank you gents. Sounds like I'll stick to paint to be on the safe side.