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Epoxy over well sanded Gelcoat?

Posted: Mon Aug 08, 2022 6:29 pm
by APLJaK
Hi, Naive question perhaps.

I am repairing the keel of a small skiff (8') for a friend. Previously someone used mat and tons of fiberglass resin and made a big mess. I have ground off the mess and would now like to use 2 x 6" 12oz tape and epoxy resin (System 3 Silvertip). The boat originally was finished in a green gelcoat. I have removed much of the gelcoat in the repair area and what remains is well sanded at 80 grit. Can I start the repair over this, even though I am not 100% back to the original glass, or should I keep sanding?

TLDR; Will epoxy resin bond over a well sanded bottom that may still have some gelcoat showing?

Better ask than find out the hard way. Thanks for any advice

Re: Epoxy over well sanded Gelcoat?

Posted: Mon Aug 08, 2022 8:03 pm
by jbo_c
I’ve done it successfully. I don’t think I’m an outlier.

As long as you’re down to solid stuff with no blisters or adhesion issues, I’d say you’re golden.

Jbo

Re: Epoxy over well sanded Gelcoat?

Posted: Mon Aug 08, 2022 8:25 pm
by OneWayTraffic
Isn't the Gelcoat more brittle than glass? If this area was under some bending stress that might be an issue.

Re: Epoxy over well sanded Gelcoat?

Posted: Mon Aug 08, 2022 9:03 pm
by fallguy1000
Keep sanding. 90% glass is good...epoxy bonds best to about 40 grit

Re: Epoxy over well sanded Gelcoat?

Posted: Tue Aug 09, 2022 11:18 am
by APLJaK
Thanks

I'll put a bit more "tooth" into the surface with 40g and then proceed.

I appreciate the advice

Re: Epoxy over well sanded Gelcoat?

Posted: Wed Aug 10, 2022 7:38 am
by wpstarling
I've done the same and didn't have issues with it sticking but there's a lot of variables that could make it different, age, type of gelcoat, how the surface was prepared to begin with, etc. Also depends on how good of a finish you want I'd think.

Re: Epoxy over well sanded Gelcoat?

Posted: Wed Aug 10, 2022 12:44 pm
by APLJaK
Glassed the bottom of the very old skiff including closing off the two giant holes in the keel yesterday. No issues.

The glass came out beautifully. I have lots of experience glassing on new glass/epoxy while building my CX19, but repairing an old boat, especially a polyester resin boat, was still new to me. I appreciate the advice!

Lucky, this is a small skiff that is used simply to transit from shore to an anchor point in the lake. Doesn't have to be beautiful, but I am very happy with how it turned out.

Might use up the last of my graphite and give it a new bottom coat while its on the sawhorses.