Alligator'd gel coat


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AlpineCoupe
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Was starting a mold today and got terrible alligatoring when I applied the second coat of gel coat.

Is this only caused because I applied the second coat too soon? Or could there have been other factors causing this mess?


Sorry the image is inverted, I'll fix it when I'm on a computer.
oekmont
oekmont
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Aligartoring is a tricky beast. Sometimes it is hard to say why it happened. But there are some things that provoke it certainly:
-Undercured gel coat
-badly mixed gelcoat (uncured  patches)
-to thin gelcoat (a second layer doesn't help here, because it is styrene based itself. It has to be a thick enough first layer)
-heavy brush lines

From your pictures I get the feeling that your initial layer was very thin.


AlpineCoupe
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oekmont - 6/5/2020 4:12:19 PM
Aligartoring is a tricky beast. Sometimes it is hard to say why it happened. But there are some things that provoke it certainly:
-Undercured gel coat
-badly mixed gelcoat (uncured  patches)
-to thin gelcoat (a second layer doesn't help here, because it is styrene based itself. It has to be a thick enough first layer)
-heavy brush lines

From your pictures I get the feeling that your initial layer was very thin.


My initial layer was pretty thin, and I was brushing it on. And I may not have waited long enough. Lots of possiblites.

Lots to learn about this composite making. ButBut at least I'm still learning with every mistake!

beliblisk
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When i apply gelcoat i do it really thin on first brush up just to make sure i cover everything and then make another pass adding to normal thickness (probably close to 1mm).Second aplication is in thickness the same as firts. This way i never had any problems so far.

Good luck
Edited 7 Months Ago by beliblisk
Hanaldo
Hanaldo
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beliblisk - 6/14/2020 6:56:59 PM
When i apply gelcoat i do it really thin on first brush up just to make sure i cover everything and then make another pass adding to normal thickness (probably close to 1mm).Second aplication is in thickness the same as firts. This way i never had any problems so far.

Good luck

*without letting it cure in between*, correct? 

This is what I do as well as it takes advantage of the thixotropic properties of the gelcoat - thin when brushing, thick when left to sit. Brush it on so that everything is covered. By the time everything is covered, the gelcoat you've brushed on already has returned to its thickest state and you can brush over the top of it and disturb it less, allowing you to build thickness easier than if you tried to go straight to full thickness.

But don't let it cure in between that first thing coat and the second thin coat, it is all done in one application.

beliblisk
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Correct. Just thin film followed right away with thicker second application (after about 2h folowed by "true" second layer). 

AlpineCoupe
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I'm glad you clarified the gel coat application.

I applied a very thin coat, left it to cure and then came back with a thick coat. Which is when I got the alligatoring. I'm glad to know that I should have applied the second coat sooner.

Can't wait to try this again, and thank you for all the comments!
Hanaldo
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AlpineCoupe - 6/16/2020 5:21:29 AM
I'm glad you clarified the gel coat application.

I applied a very thin coat, left it to cure and then came back with a thick coat. Which is when I got the alligatoring. I'm glad to know that I should have applied the second coat sooner.

Can't wait to try this again, and thank you for all the comments!

Second coat doesnt have to be sooner, in fact it is better to leave it longer if you have any doubt about the state of cure. Gelcoats are air inhibited, so they can be left up to 24 hours without issue. Even if it were left longer, a quick clean and it's good to go. But generally over night (8-10 hours at 20°) is the cautious approach.

In some conditions, leaving it 2 hours perfectly fine too, but you want to be sure you know what you're doing. Doing the second coat too soon will result in alligatoring, whereas leaving it longer won't cause any issues other than making you impatient.

Edited 7 Months Ago by Hanaldo
beliblisk
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AlpineCoupe - 6/16/2020 5:21:29 AM
I'm glad you clarified the gel coat application.

I applied a very thin coat, left it to cure and then came back with a thick coat. Which is when I got the alligatoring. I'm glad to know that I should have applied the second coat sooner.

Can't wait to try this again, and thank you for all the comments!

Just to make sure:
-1st thin application + second pass to add to normal thickness
-2nd aplication (after 1st has cured to tack state or later)

Have fun

Edited 7 Months Ago by beliblisk
AlpineCoupe
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Well it took some time but I stripped all of the ruined gel coat off of the part, re painted it, and then prepped it for the new gel coat. And this time no alligator-ing! And those spots in the middle that look like they don't have any gel coat are actually a reflection from the window just out of frame, don't worry :-).

To those of you that posted before, thanks for the help and support!!



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