varnish over epoxy issues

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amyb
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varnish over epoxy issues

Post by amyb » Fri Jun 10, 2016 11:37 pm

OK,
so on my cedar strip canoe I aplied the first coat of varnish over the epoxy on Tuesday evening and it's still tacky 3 days later.

I used west system with fast hardener as it is an unheated area I'm working in - not great humidity levels either, ephifanes varnish about 5% thinned with white spirit.

I tacked down with white spirit to clean any sanding residue from the epoxy. The epoxy has had 2 or 3 weeks of cure time.

I've seen pages with similar issues, some talking about the fast hardener being a cause, others mentioning amine blush, others mentioning using branded thinners and that some varnishes aren't compatable and options for trying terebene or cobalt driers.

I feel that if it hasn't dried now it won't so I think I will get some acetone and scrub this coat off.

then I suppose do some tests before a full coat, I can give the epoxy several soapy water rinses and test I could not thin I could add driers, or buy some other varnish for the first coat.

Anyone experienced this before and any advice to share?

hoping to get it ready to bring to Clewedog, having just agreed to crew the FD with Julian.

Amy

Rupert
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Re: varnish over epoxy issues

Post by Rupert » Sat Jun 11, 2016 8:40 am

I have had this, and I left it for about a week before it hardened, but in the end it did get sandable. Doesn't mean it always will, and I never found out why, but I think it was the epoxy under rather than the weather. Had it with G4 and varnish once, too.
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trebor
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Re: varnish over epoxy issues

Post by trebor » Sat Jun 11, 2016 10:29 am

I spoke to our paintshop about this, what they believe's happened is Epoxy "surface" set to quickly trapping thinners etc behind it, probably caused by heat or sunlight, the thinners leaching out is preventing your finish from setting it will eventually set.
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Ed
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Re: varnish over epoxy issues

Post by Ed » Sat Jun 11, 2016 10:37 am

Yes, I have had it, although not recently and I don't remember the details at all. I think I just cried for a couple of weeks, by which time it was a bit closer to drying and then left it a couple more by which time it was OKish. In UK humidity, it can take sometimes take many days to harden fully. I would certainly leave it a few days longer to see what happens.

In general, with both epoxy and G4, you need to both abrade the surface and wash down with soapy water and then lots of water. I think this works better than using any solvent for surface preparation. If you need to wipe down, then use something that isn't too oily like acetone rather than white spirit. G4 in particular seems to prefer being left for a few weeks before varnishing. Don't always do that!.... but think it is best.

Shouldn't be any problem with Epiphanes over epoxy.

Personally, I do normally use Epiphanes thinners, at least till I have run out of it. I wouldn't use a drier, as shouldn't be necessary. I would make sure you stir the Epiphanes properly. Just because it is clear doesn't mean it doesn't need to be stirred.

For what it worth, I really don't like using fast hardeners. They are just so much harder to use than 'slow'. I have a small bottle I use just for gluing sometimes, but never for laminating/coating.

Good luck,

I am sure it will sort out.

Looking forwards to photos

eib
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amyb
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Re: varnish over epoxy issues

Post by amyb » Fri Jun 17, 2016 7:50 pm

So I ran some tests on the inside of the boat,

I washed her twice with soapy water and rinsed well, then did some tests of unthinned to 50% with white spirit and did the same with a batch with some terebene driers in.

The terebene set dried in 12-24 hours, the others about 48hours. so I think the washing helped, and the white spirit is ok to use to thin.

After spending more than 4 sessions with whitespirit , rags and scrapers removing the unhardened stuffthis morning I scrubbed the outside, and put on a coat of varnish with a little terebene and a little white spirit which seems to be setting nicely. Hoping to get it finished before coming to Staunton Harold so It can harden over a week or so before some trials here and bringing it to Clewedog.

Amy

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