I have the rails of what was a 12’ sailboard blank, that lost its center to create a fishing board blank. I got these two pieces of foam b/c they looked like they’d make a nice narrow paddleboard.
Now I realize (after looking over a raft of paddleboards after a race) that an 18" wide paddleboard is gonna probably be too narrow, so I will have to widen the blank. Likely I will insert about 4 inches down the middle, but this may be tapered to nothing at the front and back.
Due to the relatively high cost of Clark foam for an insert, I’m thinking to use Home Depot EPS. Cheap, shape-able, flex not a problem, glassing will be sufficient, whatever that is.
Problem is, of course, that I can’t use poly resin over the EPS, and I don’t want to buy a bunch of epoxy that I don’t normally use (I have 5 gallons of UV poly in the garage, so it’s not the time to switch). So… has someone effectively sealed EPS for a poly glass job, and if so, how and with what?
Or, can I lam a strip of 4 oz with epoxy down the middle over the EPS, then continue with poly over it?
i’ve done 8 boards with poly over epoxy successfully. you have to seal all pinholes with epoxy. I have done 4 boards trying poly over epoxy VERY unsuccessfully. I dont’ know the chemistry of it, but some epoxies are not compatible with some poly’s , or visa versa. I know that System three epoxy is not compatible with the gloss coat I bought from Fiberglass supply.
I do know that Surfsource Epoxy is compatible with the Surfsource poly . Thats all I know about that. And also, epoxy is like a box of chocolates…
Epoxies containing phenol are the ones that polyester won’t work over. Both RR and FH resins are phenol free and will work. As HD foam is very weak I’d put a layer of epoxy with 6 oz over the middle EPS and make sure it’s nice and wet so it’s sealed well. Do a light sand and you should have no problem with your poly lam on top.
Greg has given you the definitive answer to your question. The early Hobie foam boards were styrene based foam that were sealed with epoxy and sanded, then glassed with Poly. Sometimes there were little disasters. A pinhole void would allow Poly/foam contact causing the foam to dissolve. That’s why many of the early Foamies had colored gloss coats.
You could also get some 1/8" d-cell at a boatyard. Use it over the center EPS. You could fair the EPS & PU foam & slap it on top, or you could plane/sand your EPS 1/8" below the PU foam. The latter would make cleaner lines of gray-on-white and might be easier to weigh down for gluing.
Glue it on with a poor-man’s vac bag (1-gallon ziplocks filled with sand - hot sand for that ‘autoclave’ look everyone’s talking about this year ) I’d use gorilla glue. Fair the edges down with a surform.
Then glass with your UV poly like normal. Divinycell is perfectly compatible with poly resin. 1 4’x8’ sheet, cut into 1’ wide strips should do ya…about $50. Or even cut into 4" wide strips if you go the insert style - you could do a paddleboard 32’ long with one sheet of d-cell
) I’d use gorilla glue. Fair the edges down with a surform.