Ive been a lurker on here for a while. Got some good info when I first signed up and made my first plug/mold/part. Then I made a bigger plug/mold/part. Im using PVA sprayed on with HVLP gun. Then Im using USComposits white gelcoat mixing in my own wax and also spraying with an HVLP gun. Then Im using USComposits poly resin. The last few times Ive been getting this reaction. can someone tell me whats happening? Thanks.
Your gel coat is too thin or catalyzed at too low a level. Best guess is too thin.
Why do you put wax in to the gelcoat
ive had this problem. ive noticed that if your first layer is curing faster than your second layer, then it does this, that could be it. maybe you are mixing different batchs of gel coat. its best to use one batch.
I have this problem too, when the gel coat is too thin, when i use crestapol.
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indeed, why?
some causes:
too thin,
not enough MEKP,
Second layer too fast,
Too much styrene in hanging in the mould.
Some gelcoats are more susceptible to couse this alligatoring or elephant skin than others.
You are using an HVLP gun. I can just about guarantee that it is too thin. Do you have a mil gauge and are you using it? Gelcoat should have a wet film thickness of 18-22 mils.
I will second the question - why are you putting wax in the gelcoat? It is not the proper procedure when spraying into a mold.
By the way, we call that gatoring (looks like an alligator’s back).
As others have all said.
Basically the resin layup you put on the back of the gelcoat eats into the gel and causes it to lift off the mould in this wrinkly way, pickling or alligator etc.
The gel needs to be thicker, better cured, left longer etc before the layup.
That’s the gelcoat shrinkage that causes the alligator. I’d venture the other direction and say too thick and too much catalyst.
If it’s too thick, too hot, and has too much shrinkage, I usually see someting different: cracks. Not that I ever whitnessed it on a mould surface though.
That’s not from gel coat shrinkage. This will never happen with thicker gelcoat.
As Susho and Fasta have pointed out, it is not too thick. Too thick and you get cracks and/or prerelease.
In the photos you can see some of the distorted areas filled with resin. Too thin of a film will not allow the gel to cure and then when the next layer (gelcoat or resin) goes on, the second layer will attack the first, causing it to wrinkle. Pinholes in the gel allow the resin to get between the gelcoat and mold surface, filling the voids created by the wrinkles.
the next layer will attack it? what do you mean? If they’re compatible resins, ie both polyester, then they don’t ‘attack’ each other right? Do you mean that since the gelcoat is not cured enough, that the the second coat of resin then dilutes or dissolves the first?
I’ve had too thin gel coat cure just fine, so long as you can be patient enough to wait for it to cure. I know how it is to want to get started, and not give the gelcoat enough time to tack cure and then have the resin wash away or dilute the gelcoat.
Really you can’t be sure if it’s too thick unless you measure though… just eyeballing it only works if you’ve done it a bazillion times.
also in reading the first post… why are you mixing in wax? I’ve only done this for lam resins that will be the final layer so they’ll cure.
Polyester isn’t really polyester compatible until it’s reached a sufficient cure. Styrene is the scourge of my life. The styrene in the second layer attacks the first layer; same as it would single pack paints etc. The first few times I used my polyester tooling gelcoat, I let it cure to a tack the same as I did my epoxy gelcoat and then applied the next layer. It alligators like crazy. Since then I’ve learned to let it cure to that tack, then give it another hour on top of that. Still occasionally get some slight alligatoring as I haven’t totally got the hang of adjusting to suit weather conditions, but generally that method works well.
As for the wax, I concur. I only use wax when I need to make a repair to the surface of my mould and need it to cure, I don’t use it in the making of the mould.
Well, the second layer doesn’t come after the first layer with a chainsaw or a machete 
but it does, in essence, attack the first layer when that first layer is too thin. I don’t know the exact chemical action going on but that doesn’t really matter, the main point is that it does happen and there is a solution to the problem - 18-22 mils wet.
Hanaldo,
If you get a sufficient film thickness, you should not get any gators after the gelcoat gels to a tacky, non-transferring hardness. We generally lay up within an hour of spraying. Of course, being in south Florida helps with the cure times most of the year.
Yes I imagine it can be done and spraying would make it a lot easier to achieve, but I’m all brush application so it’s difficult to get a nicely uniform layer thick enough. Especially with the gelcoat I’m using, I really don’t find it thixotropic enough. All part of the fun!
Thanks for all the replies. I was kind of in a hurry for an answer and when I went to post my question it said the modorator had to OK it before it posted. So I did an image search on Bing and found a similar picture then found possible answers for my problem. Sinse then Ive done another part from the mold and it worked perfect. I did everything the same except I shot the gel coat thicker , exspecialy around the edges where I was too thin before.
Now please school me on gel coat wax. I thought it was needed for a hard surface. No? Im shooting one thick layer with my gun. Not multiple layers of gel coat.
Are you talking about wax additive or are you really talking about hardener (MEKP, catalyst, intiator, kicker, etc)?
Provided you are actually talking about wax additive the following would be relavent:
When you are applying gelcoat in a mold with the intention of laminating over it, wax is the last thing you want mixed in. Gelcoat (and laminating resins in general) are what is referred to as air inhibited. The surface, when exposed to air, remains in a semi-cured state so that follow-on materials will chemically bond to the surface.
Wax, along with other additives designed to do the same thing, caps off the surface to exclude air, thereby allowing the material to cure through. In addition to the full cure, wax can be considered a contaminant as far as bonding goes. It will prevent good adhesion.
OK , no wax , thanks.