Help with gelcoat please.

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kev1969

Well-Known Member
I’ve made a helmet using gel oat backed with fibreglass, the problem is it had a lot of issues. There a holes as if the resin has eaten the gelcoat away, am I not using enough catalyst? Is the gel coat itself to thin? I’ve added a couple of photos of the issues I am having, any help would be much appreciated.
 

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division 6

Master Member
From what I see, probably.
I have only limited experience in glassing so I'm hoping the seasoned veterans on the subject will weigh in.

Hold tight.;)
 

Duncanator

Sr Member
I'm guessing the gel coat was a bit thin, especially if you are seeing the glass fiber texture coming through.

It also looks like there was possibly some delamination that happened? Or surface crazing?
There is a surface curing agent that can be added if this is polyester resin that might help with crazing.

Delamination could be caused by a few things: accidental barrier coat, non-wetted fiberglass, old resin, etc...

Don't know if those are your issues, but those are my best guesses from the pics. I hope that gives some help.
 

Pro Mod

Well-Known Member
RPF PREMIUM MEMBER
As you can see the fibreglass mat I'd say the gelcoat layer was way too thin. How many coats did you give it? Two coats is usual.
 

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MondoJon

New Member
Gelcoat is evil!
I built over 15 full size replica Daleks. I have seen more of this than I like to think about. Gelcoat hates humidity. That will wrinkle your piece. Also, gelcoat can be very temperamental as to the thicknessits been laid down. I suspect if you didn't have humidity issues that you didn't get the gelcoat down evenly. The best thickness is about as thick as an American dime which is a hair less than 3mm.
Hope this helps.

MondoJon
 

kev1969

Well-Known Member
As you can see the fibreglass mat I'd say the gelcoat layer was way too thin. How many coats did you give it? Two coats is usual.
Thanks division 6 for the bump and thanks to everyone for the advice. It was just one layer, newb question. I guess i wait for the gelcoat to dry before adding the next layer?
 

Pro Mod

Well-Known Member
RPF PREMIUM MEMBER
Gelcoat takes around an hour to cure when catalysed at 2-3%. At this point it should be firm with a tacky surface. Now you can add another coat and when that's reached the same stage as the first you can begin fibreglassing.
You can delay adding the fibreglass for up to twelve hours, just so long as the surface remains tacky as this aids the bonding process.

Gelcoat doesn't add any strength to a moulding it's merely a surface finish. In fact depending on the application thick gelcoat can be prone to cracking.

Hope this helps.
 

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