I have laminated a polyiso (which I think is basically unbleached polyurethane) blank with greenlight bamboo cloth and RR epoxy. Only the hotcoat is left.
Now I learned from other posts here that the standard RR epoxy doesn’t have UV inhibitor in it, which will result in browning and possibly shrinking of the blank when it’s exposed to the sun. The posts I found don’t all agree; some say poly blank + RR epoxy yellows less than poly blank + PE resin, others say the blanks turned brown and nasty.
Many of the posts were from around 2004, I’m hoping people have accumulated more experience since then, and can give me advice on how to save the board. How bad is the yellowing/browning really?
The current board is anyway not white, the polyiso foam + bamboo combo has a light yellow color that I actually quite like (see picture). And the bamboo cloth is supposed to be somewhat UV filtering. Can I just keep going without UV inhibitor, or will my board brown and crumble and shrivel?
Here are options I’m considering:
get the new “blue” RR epoxy with UV inhibitor and use that in hot coat
hotcoat without UV inhibitor but use some UV-blocking varnish or paint after board is done
use pigment in the hotcoat
keep going with regular RR epoxy also for hotcoat, if the bamboo is UV resistant enough???
Keep going. We only use EPS with RR epoxy and bamboo and have no problems with browning or shrinking in boards that are up to 2 years old. So I’m certain there will be no problem with a Poly board.
The bamboo does have a natural UV inhibitor to protect the foam to some extent. The epoxy itself may darken but it is not noticable due to the bamboo’s tan tint.
We will be stocking Resin Research “Blue” UV epoxy resin beginning in October to provide 100% UV protection for boards glassed with bamboo as well as traditional fiberglass.
Let me know if you have any questions on finishing your bamboo glass job. Glad to help out.
Thanks for being so helpful, both here, and I our email correspondence.
To clarify: It’s browning of the polyiso blank that I’m worried about. The people who reported blank browning on swaylocks in the past were the ones who used epoxy over polyurethane blanks, and polyiso is almost identical to polyurethane. (The reports on EPS + epoxy have been much more favorable. Browning does not seem to be a concern with EPS and RR epoxy. I’m also not worried about slight yellowing of the epoxy layer, as you say the bamboo already has a slight tint to it anyway, and I like that color a lot.)
Since polyiso is basically unbleacked polyurethane, I suspect it is even more UV sensitive than polyurethane: I noticed that after leaving my foam block in the sun for a week it had already discolored significantly. So that’s why I’m a bit worried.
Any comments on recent experiences with RR + polyurethane or RR + polyiso would be most welcome!
I have been using RR epoxy exclusively over my balsa compsands for the last 2 years and have had no problem with darkening of the wood, in fact the wood stays much lighter than other epoxies I have used. Thus I am surprised to hear that RR has no UV inhibitor (Greg, anyone?)
Some of my boards are sprayed with speedcote matt, which I assumed had no UV blocker?
Yes, it’s probably better to go with some UV protection rather than to be sorry later.
Does anyone know if “blue” RR in hot the hot coat would be enough protection, or am I better off applying some varnish or similar after the board is done?
If I can’t figure it out, then I guess I’ll go for resin pigment or just paint the whole board to be safe. But some transparent protection would be ideal, as I like the current color and look of the board.
Can someone here recommend a transparent UV protection product that I could apply after a RR hot coat? (I’d like to avoid getting into polyester resin.)
Not sure if just pigmenting will provide enough UV protection. If the hotcoat is transparent, that indicates some amount of light is getting through the glass and bouncing off the foam.
Whether the UV wavelength is being absorbed by the tint is probably determined by tint color? I don’t know.
The new RR BLUE resin was created for just this situation so I’d just go with that instead of the hassle and uncertainty of other methods you’re thinking about.
If you can wait a week or two to hotcoat your board I’ll slide you some RR BLUE to try out.
I’ll send you a PM.