Varnish on West System epoxy?
I recently repaired a broken cabinet on my boat and took the opportunity to strip the old varnish in order to refinish the it. I was surprised however, that the varnish doens't seem to dry (it is left sticky) on the areas with exposed (105/205) epoxy. The varnish I used was International Goldspar Satin in a 50/50 turpentine mixture. Guess I should have researched first. Afterwards I read from West's site that you should use 207 Special Clear Hardener if you are planning to varnish... And varnish with two-pack...
What are your thoughts? Should I sand the varnish away and apply a layer of 105/207 and then varnish with two-pack?
When I dismantled our tiller a couple of seasons ago - I drilled & dowelled the two halves before sticking it back together with thickened West Epoxy.
There was a nasty mixture of crumbly varnish & water marks all over , so after sanding it back to clean wood I applied several coats of thin West Epoxy, doing nothing special other than making sure it cured well after the last coat.
Some minor un-even-ness -I sanded flat with 600 wet/dry. Then I put a couple of coats of (ordinary!) exterior anti-UV gloss varnish. After a decent delay I flatted that off and used polishing compound to finish.
It looks fine, and if i need to do it again some day - I'd probably just do the same.
I perhaps should have checked the "proper" way to do it? but didn't
Was there any bloom on the epoxy? Did you wipe clean with acetone? That could have helped?
If it is sticky, I'd try wiping it off with Acetone ? let it alone for a good while - somewhere warm & dry, sand gently & try another coat??
Hi Graeme, thanks for the hint. Being somewhat wet behind my ears when it comes to epoxy, I didn't wipe it with acetone of with any other substance than sand paper. The epoxy was probably bone dry, but I just didn't think of the amine blush! You live and learn. I'll have another go at it and report...
The effect is termed amine blush. The film is water soluble, but perhaps acetone is also OK, as said above.
PU varnishes seem less affected compared with traditional oil based varnishes in my experience.
No need to use epoxy on internal work. Is the epoxy from adhesive in joints? If so then try to remove it where it runs over onto surfaces you want finished bright. Usually there is no problem varnishing over epoxy but it can go dull because UV affects the epoxy unless you use a UV resistant varnish. The lack of curing of the varnish could well be caused by amine blush on the cured epoxy which should be washed of and cleaned with acetone before overcoating.
I did the exact same thing a couple of years ago on some teak in our cockpit, actually using identical materials - west epoxy and goldspar varnish (to give UV protection). Had no problems at all, but the "epoxy bloom" was removed first by washing in warm water and sanding with fine wet and dry sandpaper and then thoroughly drying before varnishing. If the epoxy bloom was not removed first then this may be why the results have not turned out as expected. If still sticky I would remove with turps and then prepare as above before re-applying. Also heat helped - I did this in the winter but applied the epoxy and varnish in the house so left it near the boiler flue to assist curing.
Amine Blush is only water soluble (warm water and a gentle scrub with a green pad), not acetone.
You can varnish over west epoxy with convention varnish, but don't thin it. Only thin for the first coat onto bare wood, and then only with 10% thinners, not 50:50. Two pack varnish can also be used as the west epoxy makes for a very stable, hard 'base', so 2-pack is really happy. So if you had made a ply / epoxy dinghy, then 2-pack varnish would be ideal, but on something like a tiller, you can use either.
Never thin West epoxy with anything. If you want it less viscous, then warm the wood (not the epoxy) before you apply the coating. Warmth is the only recognised way to make West less viscous.
And never vary the ratio of hardener and epoxy from the correct proportions. I read else where on these forums someone suggesting you could increase the amount of hardener in cold weather. That's possible with polyester as you're only adding a catalyst, but the two parts of epoxy must combine chemically in exactly the proportions they were designed to use.
Used West to do my washboards a few years ago, with varnish on top a week or two later. Took ages for the varnish to dry properly (days if not weeks in the airing cupboard), but it went in the end. Results have been excellent in spite of the wait.
Thanks for all the comments! I really didn't remember the amine blush even though I must have read about it somewhere
I used epoxy only as a glue and stupidly enough didn't wipe the excess away, just spread it on the wood without a second thought. Luckily those areas are inside the cabinet, but I guess that my mistress don't want to have sticky clothes so something has to be done.
As for thinning the varnish, the 50:50 was intended for the first layer as I had completely stripped the old varnish away.
I think the way to go is to remove the varnish from the affected areas and wash and sand, n'est pas?
'Conventional' varnish does sometimes take a very long time to harden on top of epoxy.
It seems that taking the work outdoors to fresh damp air and GENTLE UV light (e.g. winter sun) helps a lot.
In general, it seems either 1 or 2 pack polyurethane is better than anything containing Tung oil over epoxy.
I don't know the chemistry, but the above is a precis of the advice from several trusted sources.
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