This topic has been covered a bit in the past, but mostly 10-15 years ago. I’m wondering if there’s any new theories on this that may have come to light in the ensuing years.
Basically I’m taking about the yellowing of Epoxy/EPS surfboards. This is not an issue I have encountered, but it appears that a number of people have. There is an interesting topic on the Swellnet site about it. https://www.swellnet.com/forums/wax/497925
Yeah so if anyone has a bit of time in their hands they might want to check out that topic and see what I’m on about. At any rate it’d be interesting to hear from someone who knows what they’re taking about. I have absolutely no idea why this would happen. (the yellowing) My EPS/Epoxy boards are not in the faintest bit yellow, even after a number of years of use. They just stay white. I’m using pretty standard EPS and pretty standard Epoxy surfboard resin. I don’t seal my blanks.
Any board spray finished with an automotive clear coat will yellow. So that would be Surftech, Boardworks, NSP etc. More noticeable on white or clear boards. Less so on colored or boards painted various colors. To see an example, just take a look at any white Boardworks or Bonga Perkins model that is more than a year or two old. If you sand off the clear coat; the bright white paint will be revealed.
Surfboard epoxy resin has typically been UV stabilized because it’s almost never coated with an opaque paint.
The factories in thailand typically use non-stabilized resins because they have been painting them for ages, if they now suddenly stop doing that and keep using the same resins, you get a lot of yellowing.
In the past I had quite some yellowing too, because my composites store did not sell stabilized resin. But now with the epoxy river table hype, they caught up and have quite nice and stable resins, also for laminating. Since then, never had any yellowing anymore (a UV blocking varnish also helps).
It’s just a resin formulation thing, standard epoxy resins typically yellow very fast.
All plastic yellow more or less under uv. Most pigments color modify more or less under uv too. UV blockers reduce this more and more so it became less a problem for last epoxy system plus boards are more and more colored. Make a yellow board and you’ll not have this problem even if color change slightly with time. Clear sprayed sanded lap of chinese production boards yellow badly with time but those boards don’t resist too much time…
I read swellnet link. UV deterior epoxy , UV blockers reduce this. Last gen reduce yellowing better too. Over heat yellow epoxy too. Lightly off epoxy mix, not well mixed epoxy will yellowing more or not uniform too, that’s hardener that yellow in epoxy. Most industrial epoxy build (boat, plane…) are painted to protect composit layers from uv so not needed those high cost additif in the mix. Same for car paint style epoxy boards. Epoxy they use is still yellow…