polyester gel coat over epoxy

[Richard Jones]

A weird little side project has me repairing some swimming pool coping pieces,for a friend, with epoxy and tape. Question: Since my friend already has some polyester gel coat on hand, can I apply that over the epoxy? Will it bond? How'd I get into this? He lets me test float my canoes in the pool! Thanks.

[Jim Ledger]

The general rule of thumb is that epoxy will stick to polyester, but not the other way round.

Even so, a test piece is always a good idea.

[boattruck]

Pool Guy, That is a negative, my understanding is that you can't go this direction, if you had done the repair with vinylester you could do it, but with epoxies you are bound to stay with epoxies on out to the paint...The good news is that the epoxy repairs are meant to be markedly stronger, Best of luck, Cheers, BT

[Ray Frechette Jr]

Epoxies invariably have unreacted amines on their surface. Unreacted amines prevetn proper cure at the molecular layer of the gelcoat. The glecoat will look fine, but at the very interface between epoxy and gellcoat it will not cure properly and that is why you do not have appropriate adhesion.

You can of course use some sort of barrier coat on top of the epoxy that acts as a tie coat by isolating the unreacted amines.. Then apply the gellcoat on top of the tie coat.

Interlux 404/414 stink paint makes a descent tie coat...

Pretty pricey though for a small area...

[D Happ]

What I did was make sure the epoxy is cured. Heat the epoxy for a few hours at 120F. (I heated mine overnight) Let it cool. Wash it with water. Sand it 220 and spray the gelcoat.
So far it has worked on this little boat. 2 years now and it has not a problem.
The repair area is right between the two hand holes and up over the gunnel. If you look close, you can see a small color difference. The camera picked it up, but I can't see it with my eyes.

There is a video West Systems has on youtube explaining how to put gelcoat over epoxy.

My two cents.

http://users.gotsky.com/dhapp/pirateer/repair.jpg

[RodB]

System III Clearcoat and SB 112 both allow you to apply polyester gelcoat on top because they do not release free amines. They are not cheap, but they work.

I use Clearcoat when I am doing fiberglass boat repair and want to apply gelcoat at the end.

RodB

[Richard Jones]

Thanks everyone. Think I'll put some white pigment in epoxy and use that. Doesn't have to be perfect.

[Bob Adams]

The problem with topcoating with epoxy is the sun will reek havok on it. (epoxy dosent do well with UV rays) I'd suggest an epoxy primer paint, I'd bet the polyester would adhere to that. Worth a test patch anyway.

[Todd D]

My experience is that you will be OK for small patches (a few square inches). For larger areas, I would paint the part.