Epoxy Yellowing

General Discussion
1

Hi all. Don’t usually post here as I’ve always been able to find my answers in a search.

I’ve read through the threads here on this but couldn’t find a definitive answer. What is the standard, if any, for keeping epoxy from yellowing? I’m just about to start my first batch of eps/epoxy boards; but several weeks ago had to do some extensive repair on a EPS Arakawa (chinese kind). The resin(FGH 2:1) in the repair area has since yellowed quite a bit compared to the rest of the board. This is the same resin I will be using for my own boards; and I’d really like them to stay white for more than a month.

Do I need to watch my measurements more carefully? Add some kind of UV inhibitor/stabilizer? Just change resins? The original epoxy on the board I repaired is still very white after months… the FHG resin I put on is now almost a brownish tea color.

2
Quote:
...resin I put on is now almost a brownish tea color.

So what’s so wrong with a board that matches your teeth? Seems a strange thing to obsess over…

3

Are you sure it is the epoxy thats turning brown? Could it be the filler or water coming up to the surface? I never had FGH 2-to-1 go yellow in less that a month on me. Check your ratios.

D

4

Tea brown is not yellow by the way… slight yellowing could have different reasons than downright browning.

My guess would be all these things you would find in the archives:

  1. exotherm/excess heat

  2. dirty mixing cup

  3. insufficient mixing

  4. crappy epoxy (as in poor recipe for unshielded use, i.e. boat epoxy)

5

try the Green Room resin.It was developed by some chemists out of the research triangle.we use it at WRV and our yellowing problems have ceased

6

as I understand it your options are:

  1. buy a UV stable epoxy

  2. go over the epoxy with a UV stable material

I’ve been using poly over epoxy and it’s kept the MAS from going buttery gold…but poly over epoxy

is a whole can of worms in and unto itself.

7

Resin Research sells an epoxy that is UV protected. It has a slight blue tint to it, and the result is a very bright white look for the foam.

I agree that the yellowing may be from some other source. My first guess is that there was water still in the foam. My second guess is that the epoxy went off too hot. If epoxy gets thick it heats up in a scary way. Smoke and melting things.

For deep dings, it’s best to cut out a uniform hole then fill it with a scrap piece of foam cut to fit the hole. That way you glass in the same thicknesses as regular glassing and you’ll know what to expect.

I did a large ding repair on the nose of one of my boards recently. The new foam was very obvious, because it was very white compared to the rest of the board. So I just wrote right on the foam, “Really Obvious Ding Repair Inc.” I actually like that better than a perfect repair for that board.

Doug

8

I’m fairly certain that it’s not water or filler. The damage was out of water.

The new FGH epoxy is distinctly, uniformly darker throughout; even over the original resin. You can even see where it feathers out into the existing glass job.

I don’t believe RR is an option for me on Oahu?

If the FGH 2:1 is not prone to yellowing, it would lead me to believe my ratios were off. I just went off the graduated markings on the mixing cups. Fast hardener in first; then corresponding amount of resin.

Guess I’ll just give it a shot. Thanks for the help. Working on pics.

9

Do you have a scale? Try weight ratios. It’s more precise.

10

glassing with epoxy over a white foam blank ! Hint !(fiberglass Hawaii 2-1) tint the resin with a white pigment . You will have to experiment to figure out how much white pigment to use, dosen’t take much. Wood_Ogre

11

It has been my experience that epoxy harder get darker with age. Most harders only have a shelf life of 12 months, so my guess is you mixed up some old stuff. JMHO