Gelcoat over epoxy?

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1 year 2 weeks ago #40495 by zachhandler
I went to a local composite repair supplier to get a bit of white gelcoat to put over a repair i did with epoxy and carbon fiber. The salesperson was adamant that the gelcoat would not adhere to a cured epoxy laminate and said it might even eat a hole in the boat. Obviously I know gelcoat repair has been done over cured epoxy many thousands of times the world over and it works. The sales person refused to make the sale. Am I missing something here? I plan to rough up the cured epoxy with sandpaper to get a mechanical bond with the gelcoat. Any wisdom appreciated!

Current Skis: Epic v10 g3, NK 670 double, NK exrcize, Kai Wa’a Vega, Carbonology Feather, Think Jet, Knysna Sonic X
Former Skis: Epic V12 g2, Epic V12 g1, Epic v10 double, Nelo 550 g2, Fenn Elite S, Custom Kayaks Synergy

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1 year 2 weeks ago #40496 by mrcharly
Replied by mrcharly on topic Gelcoat over epoxy?
I'd be inclined to phone them, speak to someone more senior and rat out the salesperson.

You aren't missing anything, they are talking complete and utter nonsense.

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1 year 2 weeks ago #40503 by Ranga
Replied by Ranga on topic Gelcoat over epoxy?
Technically speaking, NO polyester gelcoat does not stick to epoxy. However we do it and it works just fine, the epoxy has be be fully cured and well sanded.

What makes it bond even better is smoothing out the patch with filler, the slightest amount left on works just fine. Also you have to put on a lot to get it to harden, once hard it can be sanded back, too thin it will not set.

Trying to make an epoxy boat with polyester gelcoat, all bets are off, not even worth trying.
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1 year 2 weeks ago #40505 by zachhandler
Replied by zachhandler on topic Gelcoat over epoxy?
Thanks Ranga - your expertise are much appreciated!

Current Skis: Epic v10 g3, NK 670 double, NK exrcize, Kai Wa’a Vega, Carbonology Feather, Think Jet, Knysna Sonic X
Former Skis: Epic V12 g2, Epic V12 g1, Epic v10 double, Nelo 550 g2, Fenn Elite S, Custom Kayaks Synergy

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1 year 1 week ago #40508 by mrcharly
Replied by mrcharly on topic Gelcoat over epoxy?
West systems even have a video for applying polyester gelcoat over epoxy.

www.ecfibreglasssupplies.co.uk/video-app...ng-west-system-epoxy
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1 year 5 days ago - 1 year 5 days ago #40524 by zachhandler
Replied by zachhandler on topic Gelcoat over epoxy?
I got the repair done. Gelcoat over cured epoxy was not an issue. I used 2 layers of carbon, faired with epoxy thickened with microballoons, then did gel coat. I did a second layer of gelcoat because the first was way too bright of a white. I should have remembered ranga has advised that epic gelcoat is not white it the past. I used a tiny amount of black pigment the second time around. It is close in color, though were i to do it again I think a little less black and then a touch of something warm like yellow or orange would have been the ticket. The only real visible error are the spots where i sanded through the tinted white into the bright white underneath it. I am not motivated to gelcoat it a third time. Now I am awaiting E and P stickers from epic. Regarding the over experience, the most annoying thing was the brushstrokes in the gel coat. It just would not go on smooth, and unfortunately one has to sand as deep as the deepest brush mark to get a smooth finish. I wonder if I could have used peel ply fabric on the gel coat like I did with the epoxy layer?

The pics here for some reason are in reverse order. The original damage is the bottom image and my final repair is the top:


Current Skis: Epic v10 g3, NK 670 double, NK exrcize, Kai Wa’a Vega, Carbonology Feather, Think Jet, Knysna Sonic X
Former Skis: Epic V12 g2, Epic V12 g1, Epic v10 double, Nelo 550 g2, Fenn Elite S, Custom Kayaks Synergy
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Last edit: 1 year 5 days ago by zachhandler. Reason: Order of photos wrong

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1 year 4 days ago #40526 by Ranga
Replied by Ranga on topic Gelcoat over epoxy?
You had not needed to do such an invasive patch!

Drill a few 2mm holes the length of a surgical needle away from the solid edge within the soft area (+- 40mm) and then spaced double the distance apart (+-80mm) away from first holes just through the first outer layer of the hull (1mm deep). Then inject epoxy into holes at 90 deg to surface, bend needle to help with that. Epoxy will fill the nomex and protrude out of surrounding holes and then proceed till epoxy coming out of all holes, wipe clean and tape over holes.

You will have far less finishing and a stronger patch.

And yes peel ply over the brushed gelcoat does work well to flatted brush marks, just pull edges gently to apply pressure on gelcoat, can even smooth over with straight block of wood or similar.

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1 year 4 days ago #40528 by zachhandler
Replied by zachhandler on topic Gelcoat over epoxy?
Thanks for the assessment ranga! Ill try that method next time…

Current Skis: Epic v10 g3, NK 670 double, NK exrcize, Kai Wa’a Vega, Carbonology Feather, Think Jet, Knysna Sonic X
Former Skis: Epic V12 g2, Epic V12 g1, Epic v10 double, Nelo 550 g2, Fenn Elite S, Custom Kayaks Synergy

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