TOPIC: fiberglass molds

has anybody here tried to use the dense Styrofoam for making molds. I was just wondering if fiberglass resin will eat it up. just thinking about making fins for my old freebee boat. greg

Greg not absolutely sure but I think even the dense Styrofoam will get eaten up by the resin.

Bob

Poly resin does eat styro, not sure if Vinyl Ester does, but I suspect it will too.

But I think packing tape can be used in overlapping layers as a barrier to protect the styro.

You could coat the foam with west marine epoxy. Then do your fiberglass layup.

3 or 4 thick coats of latex paint for cover, Buy the oops paints at Lowe's and HD

thanks for the ideas, I can try with a few pieces of scrap. first. greg

I have used plaster of paris for small items.

There is a foam board intended for use with resin for making plugs. The name escapes me at the moment, but a search should turn it up.

Polyurethane (rigid) foam is what you are looking for. It comes in soft (seat padding) and rigid form and rigid is used by many boatbuilders as a sandwich and also used almost exclusively for making surfboards. You can shape it/ sand it easier and better than styrene foam and use fiberglass (polyester resins) to get an excellent finish. I have not had experience with vinyl ester over polyurethane but expect it would be ok. Check first or test.

It is the styrene in polyester resin which dissolves the polystyrene foam (also called styrofoam).
If you thoroughly cover polystyrene foam with at least 2 coats of epoxy this creates a barrier to prevent the styro dissolving. It works, I have done it often.

thanks. greg