Gel coat Issue (maybe)

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#1

I just finished my second coat of gel coat for making my mold. I was about to start applying my resin and reinforcement when I saw what looked like a hair in the gel coat. I got a probe with a very sharp and tiny point to try to fish the hair out. When I did, a big piece of gel coat (relatively big, the hair was about a cm long, and the piece that came up was about 5mm in diameter).

There was no hair in there. I mixed up a very small amount of gel coat and applied it where I tore up the piece. The first photo below is the result. The area is about 2" in diameter. As you can see, it is now worse than it was before.

I then saw a couple other places where there were anomalies. When I got the camera, one of the pictures I took look like it might be getting worse as the gel coat continues to dry (photo 3). Photos 2 and 3 are of an area about 1 inch in diameter.

Is there any way to stop this? Should I continue and just fix the mold after it’s done?

#2

99% of the gel coat is good. I just bring this up to make sure it’s okay to go ahead. Thanks!

I’m using http://www.fibreglast.com/product/white-gel-coat-682/Gel_Coats for gel coat, http://www.fibreglast.com/product/PVA_Release_Film_13/Mold_Releases for PVA, and http://www.fibreglast.com/product/Meguiars_Mold_Polish_Conditioner_and_Release_Wax_118/Mold_Releases for release wax (meguiars)

#3

Looks like what we call gators. It is caused by the gelcoat being too thin on the intial coat. Probably from a brush mark. As far as the mold goes, it depends on what level of finish you want your mold to be. If the parts are something you are going to paint after molding then go with it and just repair the mold. If you really want a class a finish, I’d really consider blowing the gel and starting over.

#4

Thanks for the reply. I went ahead and glassed it. It’s just a prototype mold, not a production mold, so I’ll just fix it later. This is my first mold ever- and it was a little more difficult than I had foreseen. I put down two layers of 6 oz cloth first, and I had problems getting the bubbles and wrinkles out. The polyester resin I used is much stickier than the epoxy I used before, and it didn’t flow nearly as well. I managed to stipple out most of the problems, but there was a wrinkle in the flange area that I just couldn’t get out. I glassed over it. Should I have used a pair of scissors to cut it out?

#5

Indeed looks like alligatoring, but on a small scale. (believe me, it can be worse)

De first layer of gelcoat is undercured. The cure is to make sure the first layer has better cure, so:

-higher temperature
-thicker layer
-less brush marks
-more MEKP
-less humidity

Also, on dish shaped moulds, make sure the styrene can drain out. Styrene is heavier than air, so putting the mould on its side helps. (if it is dish shaped, bathtub shaped, boat shaped)

#6

Okay, thanks. The humidity is pretty low, but the temp is too. The layer was pretty thick, but maybe the MEKP was lacking.

Thanks so much!

#7

You can choose from the list whatever you think might be the cause. In your case it might be temperature.