Just shaped a poly blank for a display board that will be placed outside a barber shop during the day. There’s some shade but it’ll get sun exposure from mornings til noon. I know these conditions aren’t favorable but if you had to choose, would you glass with epoxy or polyester resin? Which would handle heat better? It’ll be a colored board so I’m more concerned about delams and warping than yellowing. I have a few gallons of epoxy and no polyester so I’d rather use what I have 
Appreciate your insights!
Can you paint it white?
Hey John,
Yep I can paint it white but you think I should go poly or epoxy resin? Thanks
Surfpac -
If it is a prop for in front of a barbershop and since you already have epoxy resin, use it and paint the board white. Either way (paint or not), constant outdoor exposure will eventually take it's toll. With white paint on the exterior you can repaint it occasionally? Dark colors can heat up and cause delams with epoxy or polyester but EPS foam is more troublesome. Since you're using polyurethane foam it won't be as fragile in that regard. If it's a painted outdoor prop, weight and blank cosmetics won't be an issue? I'd rough sand it and use a light touch when squeegeeing the lam. I think some boards delam because the blanks are fine sanded, the glasser tries to squeegee every last gram of resin off, and they kick the resin so fast it doesn't have a chance to penetrate the foam.
PS - I have a broken board that is epoxy over poly foam. I've left the pieces outside now for several years and since it's glossed with polyester gloss resin, it has held up remarkably well even with a lot of direct sun exposure. It has tanned somewhat but it's still in pretty good shape. With poly foam, the foam tans too. If you decide to glass it clear over a painted blank (customer wants it that way?) use a finish with UV protective additives. Genuine poly gloss or some sort of UV clearcoat will definitely help.
Had a fire at my workshop pre christmas,(losing 11 of my boards, and 3 of other peoples) and had recently done a snap repair on a pu/epoxy board, this board was close to the fire, and the only delam was on a previous repair where polyester resin had been used… so for heat resistance i recommend epoxy!
Thanks for the insight and tips everyone. I went with the epoxy. Actually glassed it with resin and different colored pigment. I guess if the color turns nasty, I could paint over it at some point down the line.
Sorry to hear about the fire jonty. Hope your workshop is up and running again. Glad to hear about the heat resistance of epoxy.
Epoxy is the way to go for the following reasons:
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Epoxy has a much higher heat resistance than Poly, you can test this with a heat gun. As a boat builder I have had to remove more fiberglass from boats and Epoxy takes twice as much heat and 5 times longer.
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Epoxy is a bonding agent, Poly is not. Most people believe Poly is a glue, it is not. Poly just fills the glass and hardnes in the shape giving the illusion that it is a bonding agent.
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Epoxy can be puddled or built up with losing minumin structual strength, Poly cracks and breaks when puddled.
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Epoxy is 100 times safer than Poly when it comes to your health when using it. It still is not safe, wear protection (gloves and good respirator) and do not eat / drink / smoke when working with it.
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Epoxy does not stink up the neighborhood, not saying you should Epoxy in your living room, but less of a order is nice for your neighbors.
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Epoxy is harder to sand but if you come at it with the right grit paper it becomes easier to work with.
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Epoxy kits usually come with pumps taking the measuring out of the equation and nothing is worse than having a coat of goop that did not cure which can happen with Poly. If you ever have this happen use Acetone and Vinegar to get it gummy but not super sticky and scrape away. Paint stripper does not work as well as you think it would.
Side note: one way to fight heat damages is to “vent” the board. This will allow the gasses and expanded air to escape when it is hot and suck in air when cool. Make sure the vents do not allow water to get in. Just keep paint/varnish over the Epoxy or Poly because they do not come with UV inhibitors in them out of the container. You can add UV to epoxy but you better off just painting.
Have FUN!!!
I would paint it. Signs get way more UV than ordinary boards and they tend to really deteriorate. Paint the outside preferable with white paint. I use rattle cans and get fine results. Try this stuff. Really high quality.
http://molotow-na.com/catalog/spray-paint-molotow-spray-paint-c-26_35.html