I am making epoxy surfboards, normally I stop after the hotcoat and sand it down to 400 wet. Now I want to try something new and make a gloss finish with polyurethane.
Is polyurathane thin enough to get a good glosscoat? Can you add styrene to a polyurathane resin? I have read a lot about adding styrene to a polyester hotcoat & glosscoat, but can you add styrene to a polyurathene resin? Is it necessary?
If you want a gloss coat then do and epoxy gloss coat. It'll be harder to get a great shine than polyester. also, you can tryPolyester gloss resin, this will be easier to get shiny.
As for polyurethane, I believe that it is super liquidy already. try minwax PU, I don't know what styrene would do. Styrene thins polyester resin, but I don't know about a polyurethane seal coat.
I know that people use pu on a sanded finish epoxy board as a sealer. If you want it shiny with a pu coat, sand to 1200 and then try pu by wiping on with a sponge or something.
Howzit Peter, Styrene is polyester resin thinner and add 10% to your gloss resin and 5% SA . It will thin the gloss resin but it will make the gloss flow and even out really nice and you won't have to sand the gloss very much before you use your rubbing compound. Aloha,Kokua
Two problems with polyurethane glossing: (1) It takes forever to dry, and you can only do one side at a time. (2) When repairs happen, you’ll need to sand it well beyond the glassing area because the brush-on and rattle can types never dry hard enough for the epoxy to stick to. Clear marine-grade polyurethane may work, but most of those products are intended for wood.
Clear automotive urethanes (UPOL, etc) are a different story, but you’ll need the equipment and spray area to do it right. They do however form a chemical bond with the epoxy, dry really hard, and little or no polishing.
You can use epoxy resin to glosscoat, but it’s a lot of sanding and the epoxy needs a complete cure. This means a hotbox or else several weeks at least.
Glosscoating with polyester resin is sometimes done, but it very often has problems with adhesion and flakes off. I have done it and not had this problem, but I sand the epoxy to 60 grit on the hotcoat, and you have to be real careful doing that.
Most production epoxy boards (except imports) are sand finishes because of the cost of UPOL clearcoating, the labor time in epoxy glossing, and the return problems with polyester gloss flaking off.