Plastic Classic Forum

How sensitive to UV is West System epoxy? In particular how soon does exterior epoxy need to be painted before the sun does damage?

winter time, up north, maybe 5 - 6 months or even longer

Summer time, down south where I live- 2 months max

If it's only gonna be a few weeks don't worry about it over much. If it's gonna be quite a while, get a can of West #420 aluminum powder, mix that into your final two coats. That will extend the life quite a bit- as much as 8 months or so if it isn't in direct broiling sun.

John,

I think you have a little more time than Charlie suggests. Here in Philly, I've left filled WEST exposed for an aggregate of a couple years. I suppose the filler kept the sun away from the epoxy deeper in. I've left neat epoxy coating on wood exposed for an aggregate of about a year. In both cases, a color shift starts pretty quickly, which I take as evidence of deterioration; obviously unacceptable for a surface which you intend to finish bright. However, I think there's a long distance between color shift and real chemical damage in a filled epoxy that would not be removed by a bit of sanding. Google on this subject; I recall finding a fellow's site showing photos of wood test panels using several manufacturer's products.

On my FD project, I keep the work-in-progress (the whole boat) covered to slow down the color shift in bare mahogany as well as in epoxy-coated surfaces. It's only uncovered in the barn when I'm working on it, and uncovered outside when I'm photographing it or turning it around. I'm pretty much adamant about keeping it covered since the whole boat will be finished bright. Final finish will be the WEST's special coating for bright finish #207 covered with marine varnishes. I've used this with mostly good success on some small boat parts, and with great success on interior floors and countertops.

You may be closer to the truth than I am, for where you are and from your keeping it covered.

But here, the sun can be BRUTAL, even in spring and fall. So I have to base my answers on what I personally have experienced

And of course if you are painting, you have much more leeway. But the epoxy WILL eventually turn yellow and start lifting- then you have to get rid of all of it and start over- not fun.

Hooo! I failed to notice that you are in Texas. The place is death for boat plastics, judging by those I saw on our $1000 weekend in Kemah. Even Miami did not seem so bad and it's just as far south.

Johnnyboats will be bringing his boat home to Maine from Florida, but I don't know on what schedule.

Johnnyboats will be bringing his boat home to Maine from Florida, but I don't know on what schedule.

I'm currently in Tarpon Springs on the hard, looking to get out of here before hurricane season.

On the other hand with all the snow in Maine, I don't think I want to get there before Memorial day ;-)

JonnyBoats wrote:How sensitive to UV is West System epoxy? In particular how soon does exterior epoxy need to be painted before the sun does damage?

I would not leave epoxy exposed to UV for more than a a week or two. According the Gougeon Bros, quoting from their Wooden Boat Restoration and Repair manual:

"Any epoxy finishes without protective coatings are vulnerable to rapid ultraviolet degradation. West System Brand epoxy, including 207 Special Hardener, is not intended to be used as a final finish. Therefore you should cover bare epoxy that will be exposed to direct sunlight as soon as possible with an opaque paint or a clear coating (varnish). If the surface is to be painted, add pigment to the last two coats of epoxy to protect the surface. Surfaces that receive indirect UV exposure, such as below decks, will last much longer without a protective coating than directly exposed surfaces."

I would not leave epoxy exposed to UV for more than a a week or two.

Is there soe kind of "paint" or other coating that can be used to protect a work in progress? In other words, suppose there is some exposed epoxy which will need another coat at a later date but which can't be covered with a tarp for some reason (like one wants to go out sailing for example).

In my case I glassed in three new hatches and plan on painting the topsides at a later date, but I do not yet know what kind of paint will be used. I don't want to put on a primer that will be incompatible with whatever kind of paint is ultimately used, thus I am looking for something to protect the epoxy which will not interfere with the later work of fairing and painting.

There are answers to that in a couple of the posts above: you can add certain pigments or powders to the epoxy so that it is protected, at least short-term, from UV rays. These additives are compatible with additional epoxy later, or with whatever primer you might use down the road.

you can add certain pigments or powders to the epoxy

What if one was dumb and forgot to do this? ;-)

Should I simply add another coat of epoxy with the powder in it?

Yes.

I would not leave epoxy exposed to UV for more than a a week or two. According the Gougeon Bros...

In Maine I have one skiff, which I sometimes forget to paint. Once I re-did the exterior, and forgot to paint most of it. After 3 or 4 years of 12-month exposure (6 months upright, 6 months upside down on shore) the epoxy was failing, particularly on the topsides.

I still don't bother to paint the bottom, as it needs repairs due to abrasion damage long before the epoxy fails.

Another experimental boat was West over foam. It's been outside year round for over 20 years, kinda deteriorated now, but was serviceable for the first 10 or so.