Good day everyone!

Yeh that looks like shrinkage to me. To be honest, it sort of looks like uneven post-curing. Does your oven heat evenly? Or did you release the part from the mould before doing the elevated temp? 

That might be possible, my oven isn't very precise, and I did instant jump from 50 to 60C, I kept the part inside the mould and released only after postcuring. Also I havent postcured the mould itself, but It heated up to 70-80C when laminating, so I thought it wouldn't need postcuring anymore.

HI Zymka,

Have you tried without the Styrene? I suspect thinning down the GC50 has meant that during the cure it has pulled from the surface a bit more perhaps shrinking back a bit more as the extra styrene evaporates off during the cure.  Also the GC50 is typically the correct viscosity for spraying onto a mould so thinning it down may have reduced the surface tension of the gel making it more prone to pull away from the surface like you have seen as it cures.

We do not recommend thinning of GC50 with styrene in the majority of cases.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

I haven't tried without thinning for bigger panels, as I liked the flat surface when I sprayed thinner gelcoat. Perhaps this is the problem. I will spray without thinning next time.

You can sand it no problem, just be careful not to pre-release it from the mould surface if you're using a high slip release agent. 

Yes, I like it when its flatter , because the top layer looks much better when fillaments are laying straight, I don't know how to say , you know when you brush gelcoat with a brush, you get uneven surface of carbon beneath the gelcoat, so when i spray it without thinning I get some hills and holes, which will be visible as well, especially when using 12k carbon weave.