Gelcoat nightmare

[cme4pain]

I was patching up last years gouges and scrapes on the front of my boat.

Sprayed evercoat brand gelocoat over the repair area thinned with 10% acetone. Certain parts of the gelcoat didnt catalize. Thinking I screwed up mixing, I took it off mixed up another batch and mixed with my drill attachment, thinned and resprayed. Same problem.

Can it be that I used colloidal silica in my fairing compund, gelcoat not compatible with epoxy. I cant think of anything that would cause the gelcoat to catalize in some areas and not others.

[Fanie]

Which catalist did you use and what ratio. What you describe does not make sense. If you add catalist to gell coat it is supposed to harden correctly. Done it many times, just never thinned it.

I'm not too sure about thinning the gell coat with acetone though, I've never done that.

[cme4pain]

manufacturers instructions said thin with acetone 10-15% to spray. Catylist came with the gelcoat. Quart size can I mixed a pint and used half the catylist per instructions. Its weird. On one hand I have a beautiful gelcoat but in some areas it just didnt set. Areas about the size of your hand. Thats why I am wondering if the silica in the fairing has something to do with it. But even that makes no sense. If the silica had something to do with it it probabaly would fisheye like an automotive paint or just not adhere.

[MikeV]

what type of gun did you use to spary just wondering...
spmtimes i end up spraying over it with a mixture with more hardener ????

[gonzo]

Is the gelcoat waxed?

[cme4pain]

no no wax. Sprayed with my gravity gun. I am gonna mix up another batch tomorrow from another brand.

You could put a little acetone in there but what manufacturer recommended that? Generally they have thinners specifically for that. It has been done for as long as there has been gelcoat but it doesn't even make sense, as I understand the chemistry. People used to thin with acetone to get it to partially soak into plywood which doesn't do anything. The colloidal (fumed) silica didn't hurt anything unless it was contaminated. I don't understand adding it to the gelcoat to spray, however. Was it recommended to build up faster or prevent sagging, or what? I wouldn't. RU a dentist?

[gonzo]

Gelcoat with no wax will not cure. It is air inhibited.

Gonzo is right, of course. We all missed that.

[cme4pain]

what wax? there is nothing on the can that says wax. I didnt add silica to the gelcoat. I mixed silica in with my epoxy resin for my repair and sprayed gelcoat over it.

[Landlubber]

Gelcoat over epoxy, NO.

You can epoxy over polyester, but not popyester over epoxy. and there should be waxed gelcoat for top coating , known commercially as Flocoat. It is simply gelcoat the has wax in styrene mixed in, it allows the air ti be sealed from the surface and the surface can cure.

[gonzo]

They sell the wax solution to add to gelcoat. Epoxy produces amines when cured. I don't know how it could affect the gelcoat.

[ondarvr]

You have two things that may have happened.

1. No wax in the gel coat, this will cause the surface to stay tacky, but you should be able wipe it down with acetone to remove the surface and then sand and buff it as normal.

2. The epoxy was still curing and inhibited the cure of the gel coat.


The bigger issue is that even if it did cure well and you finished the job, it may not hold well. Polyesters just don't bond that well to epoxies, it will stay in place for a while, but the chance of having problems in the future are much greater than when using compatible products.

[cme4pain]

Thank you! I figured it had something to do with incompatitable materials. I did wash the uncured spots down with acetone. Guess I will sand the epoxy out and redo with polyester resin.

[thill]

...Or just use a barrier coat?