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floatingkiwi
04-20-2009, 12:53 AM
I am aware of the detrimental effect, sunlight has on epoxy.
Has anyone actually had epoxy fail them from being exposed to the sun, what was the damage, how long, etc.

ShagRock
04-20-2009, 01:29 AM
BHOFM...in the article you linked it says:

When exposed to UV (ultraviolet) radiation such as full sun, sooner or later it discolors, turns very brittle, and eventually disintegrates.
I assume the latter indicates failure. Be interesting to know how long that takes.

AstoriaDave
04-20-2009, 02:02 AM
It definitely fails. Takes a few months of regular sunlight to become obvious to the naked eye. Probably compromised structurally before that if the thickness is minimal. On epoxy/glass covered hulls, I typically allow the boat to cure for a couple months before final sanding preparatory to application of a protective finish (varnish, 2-part LPU). Most of the time, I have not worried about the intermittent exposure to sunshine for a dry-sailed hull which is stored indoors. No ill effects, so far, with that practice.

In tropical sun, things would go bad very much sooner; I am at latitude 46 N.

Andrew Craig-Bennett
04-20-2009, 03:44 AM
It is surprising how good the UV protection afforded by varnish can be. I've just stripped back the insides of my 19 year old tender, finished with epoxy and four coats of UV resistant two pack polyurethane varnish and given one coat of varnish five years ago. The boat has gone through 19 summers at 51 deg N and the coating had failed mechanically and from related moisture ingress over maybe 12% of the total surface. I'm impressed!

P.I. Stazzer-Newt
04-20-2009, 03:53 AM
Took some early Kevlar epoxy kayaks from Khartoum to Aswan in '82 - about six weeks.

The discolouration was remarkable and the hulls were subsequently quite brittle - but its a little hard to draw any firm conclusions:
The boats were built down to weight (as asked)
The builder had relatively little experience with Epoxy, though lots with polyester.
Lightweight whitewater boats are relatively disposable items anyway.

carioca1232001
04-20-2009, 07:06 AM
It is surprising how good the UV protection afforded by varnish can be. I've just stripped back the insides of my 19 year old tender, finished with epoxy and four coats of UV resistant two pack polyurethane varnish and given one coat of varnish five years ago. The boat has gone through 19 summers at 51 deg N and the coating had failed mechanically and from related moisture ingress over maybe 12% of the total surface. I'm impressed!

The four coats of UV resistant 2-part PU varnish probably take all the credit as the formulation of the 'single coat of varnish applied 5 years ago' was not specified.

The proprietor of a boat epoxy plant in Rio told me that the epoxy holds out provided 4-to-6 coats of 2-part , UV resistant PU varnish is applied over it.

I followed the recommendation with aircraft-grade 2-part, clear, UV-resistant PU varnish, and the lot has weathered well in the boat hangar for 18 months now. Will need to see what happens when the boat is launched and sits out.

spirit
04-20-2009, 08:24 AM
Aside from sunlight, be careful of heat. I joined mahogany boards with thickened epoxy, edge-to-edge with a deep spline, for seats in a Boston Whaler in the tropics. The perfect original bond failed completely after two years exposure to sunlight, even though the epoxy was completely out of the sun.

Todd Bradshaw
04-20-2009, 10:40 AM
Gougeon Brothers say that epoxy can start to deteriorate in as little as 200 hours of exposure to sunlight. I have seen unprotected resin turn yellowish, get kind of rubbery and crumble away (reminded me of one of those art-gum erasers) within a single season. It's just not something you want to push your luck on when protecting it is a reasonable simple procedure.

Brian Palmer
04-20-2009, 10:51 AM
Lots of talk about varnish here. Don't forget that good ol' paint is also a pretty good UV inhibitor.;)

Brian

floatingkiwi
04-20-2009, 01:45 PM
Interesting.

John Meachen
04-20-2009, 03:20 PM
Took some early Kevlar epoxy kayaks from Khartoum to Aswan in '82 - about six weeks.

The discolouration was remarkable and the hulls were subsequently quite brittle - but its a little hard to draw any firm conclusions:
The boats were built down to weight (as asked)
The builder had relatively little experience with Epoxy, though lots with polyester.
Lightweight whitewater boats are relatively disposable items anyway.
I would have been more concerned about the possible failure of the Kevlar.Having had three Kevlar main halyards break in a four month period a few years ago,I prefer to avoid using it for anything.FWIW this occurred at 52 deg north.

floatingkiwi
04-20-2009, 07:08 PM
Fwiw?

mcdenny
04-20-2009, 09:02 PM
For What It's Worth

willmarsh3
04-20-2009, 09:11 PM
When I built my boat a fair amount of epoxy dripped on my saw horses. I left them outside and watched the epoxy turn yellow and eventually peel off. Later as I was making the topsides bright I used the West 207 hardener as it is designed to resist UV more than others. Nonethless I then coated it with several coats of varnish. It has held up quite well.

Todd Bradshaw
04-21-2009, 10:31 AM
You can buy UV blockers to add to resins to aid in protecting them. Look up "UV9" for example. It's a fine, yellow powder. We used to mix small quantities of it into resin as a booster. It's most likely similar to the stuff they put in WEST 207. However, it does not make the resin UV-proof. Just like the blockers in filtered varnish, it gets used up as it does it's job. Good UV filtered varnish, recoated and renewed on a regular basis, is still the easiest way to protect clear epoxy and opaque pigments, graphite and good old paint are even better.

John, your Kevlar halyards most likely failed due to internal abrasion, rather than UV. This has been a problem with Kevlar (Kevlar 49 usually being somewhat worse than Kevlar 29) since day one. If free to move about, Kevlar fibers will abrade and cut each other. On a boat layup, this isn't much of a problem because the fibers are fixed in place with the resin lamination. For a piece of woven fabric or a hunk of rope where the fibers are moving, flexing and rubbing on each other in use, it's a very different story. In sailcloth, they finally worked around this problem by eliminating the over/under weaving and simply laying directional layers of Kevlar strands on top of each other, layer-by-layer. For rope, most manufacturers have moved on to different materials, most of which tend to be self lubricating, or at least slicker and less abrasive.

wtarzia
04-21-2009, 02:25 PM
Oh, good, I was going to ask if graphite is OK. I coated my canoe's bottom with graphite-epoxy but was worried if refracted sunlight might do it in. --Wade

Todd Bradshaw
04-21-2009, 03:37 PM
Graphite works, but does so by essentially stopping light penetration close to the surface. Any little resin bits on the surface that are holding the graphite particles together and are exposed may deteriorate, but it's more of a surface chalking issue than one where the entire resin layer starts to fail all the way through. If things start to get ugly, you could probably give the surface an occasional burnishing or wet-sanding, get rid of the chalk and have a nice new-looking outer layer without removing much material at all. Opaque resin pigments, or barrier-coat particles (aluminum flakes), can do the same by simply packing the resin full of tiny particles that light can't pass through. Paint goes one better by stopping the UV before it even gets down to the resin.

Most of the normal, non-opaque UV filters/blockers that I've run into work differently and convert the UV to heat, allowing it to dissipate before it damages the product. In the process, they slowly get used up and regular recoating is required to maintain good protection and a good supply of the little blocker bits in the outer coating layers.

floatingkiwi
04-22-2009, 02:53 AM
For What It's Worth

Right.

P.I. Stazzer-Newt
04-22-2009, 04:12 AM
I would have been more concerned about the possible failure of the Kevlar.Having had three Kevlar main halyards break in a four month period a few years ago,I prefer to avoid using it for anything.FWIW this occurred at 52 deg north.


....
John, your Kevlar halyards most likely failed due to internal abrasion, rather than UV. ....

Thanks - this seems a reasonable explanation - my only experiences of kevlar has been either in laminates or as a thread in fly tying - and when loaded it is capable of cutting other materials.

Not that deer hair puts up a lot of resistance:)

Bill Huson
04-22-2009, 06:23 AM
WEST resin 205 or 206 hardener, good for about a year and then turns white and flakes off. Don't know about the 207 hardener, just started using it. I never varnished my 15 super stock hydro and the WEST resin got ugly after a year or so. Sand it down, recoat and varnish ... no wait! Gotta race to go to - forget varnish! Repeat.