Epoxy and UV light...


Enthusiastic about Wooden Canoes
I've read in a number of places that epoxy is damaged in UV light with prolonged exposures, for example at: http://www.oneoceankayaks.com/Epoxtest.htm.

I'm curious, however, if there is any threat over a few days (5-6 days w/ partial exposure). I'm varnishing the interior hull of my canoe on a West-facing porch, as I don't have access to a garage and my basement is poorly ventilated - the porch is the only thing covered. But there is a bit of light exposure from ~2pm to 8pm near the hull. I'm waiting to paint the epoxied fiberglass hull until after the varnishing is complete, but I can't cover the boat from the light when the varnish is wet. By varnishing in the AM, I've escaped most trouble with the sunlight and varnish - but I'm worried about the epoxy a bit.

Will 5-6 days of partial sun exposure do any harm at all to epoxy or is the danger only in months of exposure...?
You will be fine. Just don't push your luck. Epoxy formulas vary a lot but some can start to break down with only a couple hundred hours of UV exposure if they aren't protected. Also keep in mind that UV absorbers get used up as they do their job. Most work by converting UV to heat, which can bleed off into the atmosphere before damaging the resin. As the protective film of varnish ages, it slowly loses it's ability to protect the epoxy and needs to be recoated from time to time to replenish the absorbers.

I don't know why it took me 24 hours to think of this, but I'm also going to cover the exposed region of the hull with a loose plastic, taped on - should do the trick too. Definitely don't want to push my luck though. Thanks.