Gelcoat crinkle question?


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Kacordy
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What causes Gelcoat to crinkle about 30 minutes after applying with a spray gun? I went ahead and did my layup over this bad spot in the corner because my cut line is a 1/2 inch below the bad spot. This is only my second time making a mould. This is orange tooling Gelcoat with 15% Duratec added and 1.5% MEC. I sprayed the mould with APV and let it dry for 2 hours. I’m shooting the Gelcoat with a 3M Accuspray gun with a clear 1.8 head. I will have to spend more time with this gun. With the 1.8 head it just spits Gelcoat. A splatter gun. Thanks for your help so I can learn these processes. Allen 

antonkov
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I had the same effect but on a much grander scale. Did a research and found a post on a different forum listing all possible causes, it was a long list of factors many of which were listed twice as in too much of X or too little of X. 
At the top of the list were thickness of the layer, temperature and catalyst percentage. 

Here is a good info:
https://www.boatdesign.net/threads/gelcoat-crocodile.43007/#post-552546
https://www.buefa.ee/wp-content/uploads/2018/10/Gelcoat-trouble-shooting_eng.pdf

The keyword that might help is
"
alligatoring".

Never used Accuspray, but 1,8mm sounds a bit too small for a gelcoat. I am spraying with 4mm cup (aka dump) gun and making several passes per layer, two layers total. 
Did you follow all of the recommendations from the datasheet?


Edited 4 Months Ago by antonkov
Hanaldo
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1.8mm is wayyyyyy too small, thats too small even for primer let alone gelcoat. 

With that in mind, the issue is very likely to be insufficient thickness.
Chris Rogers
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I third antonkov and Hanaldo's larger nozzle suggestion - 2.5mm maybe.  Sometimes you can thin gelcoat with styrene to get it to flow better through a spray gun but it's also asking for trouble.  Are you spraying in one shot or multiple coats with time between?  Do you gauge thickness?  My understanding is that most alligatoring like this is caused by trapped styrene that comes from spraying too quickly over a just-gelled first coat.  The rule of thumb I was taught it to wait until no gelcoat color comes off on your (gloved) finger when you lightly touch the surface before adding more - more gelcoat or a skincoat or laminate. I've certainly had it happen when this wasn't an issue and there are many contributing factors.  Good luck and let us know if you have better luck after making some changes!




Kacordy
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Chris Rogers - 9/28/2020 2:01:44 PM
I third antonkov and Hanaldo's larger nozzle suggestion - 2.5mm maybe.  Sometimes you can thin gelcoat with styrene to get it to flow better through a spray gun but it's also asking for trouble.  Are you spraying in one shot or multiple coats with time between?  Do you gauge thickness?  My understanding is that most alligatoring like this is caused by trapped styrene that comes from spraying too quickly over a just-gelled first coat.  The rule of thumb I was taught it to wait until no gelcoat color comes off on your (gloved) finger when you lightly touch the surface before adding more - more gelcoat or a skincoat or laminate. I've certainly had it happen when this wasn't an issue and there are many contributing factors.  Good luck and let us know if you have better luck after making some changes!

Thank you for the suggestions. I just bought the spray gun and the paint store recommended the 1.8. I will up the size to 2.5. Hanaldo, your correct, the 1.8 would not allow me to build up the Gelcoat. I was fighting thinnest. I do have the Gelcoat gauge to monitor my multi layer build to 22-25 mill. I miscalculated and did not order enough Gelcoat. I went ahead and applied the fiberglass to try and salvage my project. It came out decent enough that I will hand lay-up a hull so I can start designing the deck and cowl. I will start the process over. I apologize for not posting pictures. I want to keep this design a secret until I expose it at a National Event in 2021. I race gas RC Boats. Thanks for the guidance. Allen


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