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UV and Epoxy

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#1 KelpKritter



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Posted 18 April 2009 - 09:46 PM

I know that UV rays will yellow and cause other problems with epoxy if it is not painted over. I learned this as I built some small boats using epoxy resin in the build and was told very plainly in the plans to cover the epoxy with paint.

For lurebuilding my question is two-fold. First, are there any other factors that would cause yellowing of a cured epoxy top coat other than UV exposure? Second, assuming the first answer is no, would a clear spray on top coat of some kind, over the epoxy, keep it from yellowing?

Thanks for the help.


#2 BobP


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Posted 19 April 2009 - 05:46 PM

Epoxies are almost always somewhat yellow to begin with and they get more yellow as they age. Same goes for cured epoxy. It all yellows to some extent over time. The only way to slow (notice I did not say eliminate) the process is to use an epoxy with UV inhibitors like NuLustre, or overcoat the epoxy with a clearcoat that contains UV inhibitors (which IMO begs the question "why use epoxy at all in that circumstance?"). Almost all clear finishes including polyurethanes also yellow with age to some extent. Measuring accurately and mixing epoxy thoroughly also helps to avoid yellowing. I have plenty of baits coated with epoxy (D2T) that show only negligable yellowing after several years so I personally don't consider it a big problem.

Edited by BobP, 19 April 2009 - 05:48 PM.

#3 FishThanks



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Posted 19 April 2009 - 07:34 PM

West Systems makes an epoxy now that has UV protection. My friend put three coats on a large Teak swim platform (sanding between) and then we shot two coats of Automotive clear over top. It looks amazing. A wood supplier to the boat industry told us about the Epoxy. I do not remember the number for each of the components but my friend still has the cans if anyone is interested I will get the numbers. He bought it in Quarts I am not sure if they offer a smaller can.

#4 RiverMan


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Posted 19 April 2009 - 10:07 PM

I had an envirotex lure that I left in the vehicle one time for the entire summer, it cooked very day in full sun, sometimes over 100F outside and it never yellowed in the least.

If you are worried about UV, look at EX74 by envirotex. It won't yellow anytime in the next few decades.