Epoxy is Not Forever

[Roger Long]

Well, I know that but this was still a surprise.

After I got my Puffin fiberglass dinghy at the beginning of the summer before last, I printed up a label on plain paper with my contact information. I set this into some wet epoxy and then applied more epoxy over it, wetting out the paper as much as possible, with a good thick coat over the top. I thought this would be a pretty permanent marking unless someone took a grinder to it. Wrong.

I noticed yesterday while cleaning the dinghy that the lettering was illegible. I touched the label and the top surface scraped off like a wet label from a food jar. There is still paper stuck to the hull but the rest is gone. This was up under the gunwale so a pretty dry location. I can't remember what I used but it was something like System Three or Silver Tip. The paper wasn't fully saturated but there was a thicker a layer over the top as I would expect to use in the finish of an epoxy composite wood construction.

Even when there is no standing water, moisture seems to migrate through Epoxy to a much greater extent than I would have expected.

[orbb]

Was the label in sunlight much?

[The Bigfella]

Yep, sounds like UV degradation to me.

I made a couple of carbon fibre bits for my bike in July last year. I used normal West System resins on one part and their UV resistent resin on the other. Neither piece has had any further protection. The bike has had a lot of outside exposure over the last 16 months or so. The normal resin piece has badly discoloured and degraded a bit. The other piece is still fine.

[MiddleAgesMan]

UV failure, plain and simple. Cover the area with UV resistant varnish and you'll be good.

I was slow to paint an epoxied area and I got a crazed surface within a couple months. You could brush off the broken surface with a fingernail.

[George Ray]

The Epoxy Panel after 1 year
http://www.oneoceankayaks.com/Epoxyhtm/epox12m.htm

UV damaged epoxy - what happens?
http://forum.woodenboat.com/archive/...p/t-69536.html

http://www.scribd.com/doc/60541937/152/UV-Degradation
"Chapter Six - Failure Modes
- Design Guide for MarineEnvironmental Degradation Applications of Composite"
UV Degradation
The three major categories of resins that are used in boat building, polyester, vinyl ester andepoxy, have different reactions to exposure to sunlight. Sunlight consists of ultraviolet raysand heat.Epoxies are generally very sensitive to ultraviolet (UV) light and if exposed to UV rays for anysignificant period of time the resins will degrade to the point where they have little, if any, strengthleft to them. The vinyl esters, because there are epoxy linkages in them, are also sensitive to UVand will degrade with time, although in general not as rapidly as an epoxy. Polyester, althoughbeing somewhat sensitive to UV degradation, is the least sensitive of the three to UV light.The outer surface of most boats is covered with a gel coat. Gel coats are based on ortho orisopolyester resin systems that are heavily filled and contain pigments. In addition, often thereis a UV screen added to help protect the resin, although for most gel coats the pigment itself serves as the UV protector

[Todd Bradshaw]

I used normal West System resins on one part and their UV resistent resin

While the UV absorbers in this formula make it less prone to UV damage than most other resins, their UV resistant resin is by no means UV proof and not intended to be a stand-alone UV barrier. It would still be a very good idea to top-coat the frame with a more effective UV protective coating.

[Tom Lathrop]

I made switch labels for an instrument panel that sounds just like your method. They have been on for 12 years inside the boat but exposed off and on to the sun. They are still very legible but getting kind of ratty. I plan to make replacements and either coat the topcoat of epoxy in some UV varnish or bond it to some thin plexiglass. I used RAKA but don't think that made any difference.

[Neddie Seagoon]

When I turn a bowl, I glue a baseplate for the chuck onto the bottom of the bowl blank using a piece of paper in between. When the bowl comes off the lathe, the baseplate can be easily pried off without damaging the bowl.

Paper, having no tensile strength, is not a good matrix for a composite system. Especially if it was not properly wetted. It's not the epoxy that's not forever, it's the paper.

[Todd Bradshaw]

That would depend upon UV exposure. Epoxy exposed to as little as a couple hundred hours of UV can start to break down and is most certainly not "forever". Neither are the UV absorbers in varnish. They get used up as they do their job and need pro-active renewal to maintain protection.

[Andrew Craig-Bennett]

This is a very important thread.

FWIW, I'd put the life expectancy of a very good UV resistant polyurethane finish at twenty years in the British climate - which is notably cloudy. In the tropics, make that three years.

[St.J]

Wow!
What are you using Andrew?

[Andrew Craig-Bennett]

SP Systems.

[Bill Huson]

How true. Before WEST came out with 207 I had my race boat coated with 105/206 but in the rush to go racing did not varnish. One season and finish was done. Silly me sanded it down, recoated with 105/206 and . . . whoops! Race this weekend! End of that season, finish was UV cooked.

Built two SUPs last year coated with 105/207, no varnish. The boards sleep inside and so far so good, but another build with 105/207 and two coats of spar varnish is beginning to look sad after two years, most of the time outside in the sun. You folks are right, two coats of varnish isn't enough.

Note to Roger Long: Epoxy is not exactly waterproof. I seem to recall WEST claiming 6 coats of epoxy to get a coating thickness that will be reasonably water/moisture resistant.

[Todd Bradshaw]

Naturally, the best defense against UV for epoxy is a good paint job. Sunbrella is also pretty good. I had alcohol stain, followed by six coats of WEST 105/207 and topped with Captain's Varnish on the bright mahogany topsides of my Starboat. I made a full Sunbrella cover for it and it sat outside for five years under the cover. When I moved up here, I had to get new registration numbers and was happy to see that there was no fading or discoloration around the old ones when I peeled them off.

[JimConlin]

In the Gougeon book:
http://www.westsystem.com/ss/assets/HowTo-Publications/GougeonBook%20061205.pdf

Page 21: "All epoxies eventually break down under direct sunlight, so epoxy-coated surfaces should be protected with paint or ultraviolet-resistant varnish..."