Materials that are attacked by fiberglass resin?

[Stephen Tashiro]

Are there common materials that are attacked or dissolved by the resin used in making fiberglass objects ? In other words, what common materials should be avoided in making moulds and forms for fiberglass parts?

I assume that with a suitable release agent, wood can be used as a form. Will common coatings for wood like shellac or polyurethane cause problems?

[Wayne Lomman]

If acetone affects it, avoid it. Cheers

[Lee Schierer]

Latex gloves don't hold up.....

[Alan Rutherford]

I assume you're thinking of shellac and polyurethane as wood finishes, not as release agents. Nothing comes to mind that could not be used as a form as long as it's physically sturdy enough. I'd be more concerned that your release agent is compatible with both the finish and the resin. Wax works.

[Edit: As noted below, styrofoam does not play well with acetone. Painted with something that would stand up to the resin or covered with plastic or even packing tape it should work fine.]

[Stephen Tashiro]

If acetone affects it, avoid it. Cheers

I see Styrofoam listed as a material for making moulds, but doesn't acetone dissolve Styrofoam ?
http://www.fiberglasssupply.com/Misc...materials.html

[Wayne Lomman]

Yes and the site also notes that it is not compatible with polyester or vinyl ester resins which are the common ones used. Hence the advice to stay away from acetone soluble materials. Cheers

[Pete Simmons]

Epoxy resin reacts less to many things such as Styrofoam. Items such as foam core surf boards and form core kit aircraft use epoxy resin. Polyester resin melts thru most foams easily. Of course epoxy resin costs more than polyester resin.

[Alan Rutherford]

Epoxy resin reacts less to many things such as Styrofoam. Items such as foam core surf boards and form core kit aircraft use epoxy resin. Polyester resin melts thru most foams easily. Of course epoxy resin costs more than polyester resin.

This reminded me that I once filled a large void ( > 1 cubic foot) in the fiberglass-encased lead keel of a 40-foot sailboat with 2-part expanding foam and then glassed over it with conventional mat, cloth and resin. It held up for years with no problems. I did nothing to protect the foam from the resin - didn't even think about it.

[Walter Plummer]

The two part foams are polyurethane not a styrene foam. The polyester and vinyl ester contain styrene and will melt the styrofoam. Molds can be made from wood, mdf, plastic, or even fiberglass or carbon fiber. Sealing substrates and release agents equal success. PVA (Poly vinyl alcohol) can be sprayed or brushed on and creates a film barrier that is water soluble if all else fails. Careful design to prevent under cuts is very important or your hard work remains locked on the mold. Even with good draft and proper release you will be surprised how difficult it is to get a release sometimes. Lots of wedges are very handy to have on hand.