Molding Styrofoam

I do a lot of vacuum forming. I usually cast all my parts in plaster. I want to make a mold of a piece of styrofoam. I don't think I can poor plaster into the styrofoam without ruining the original mold. Can anyone think of some other options?

You would have to maybe fiberglass the foam part, to give it a finish?

You can make a rubber mold of the styrofoam and pour plaster in that. Smoothing over the surface irregularities with some other material would produce a smoother part ultimately, but you can't use regular fiberglass resin, which is polyester and dissolves styrene-based foams. Joint compound might be a better choice. Of course, you can also sand the plaster part after it's removed from the rubber mold, if the dimensions aren't critical.

Andrew Werby
ComputerSculpture.com ? Home Page for Discount Hardware & Software

you can also metalize it

the1toyplace, If you are looking to make a rigid mould there are better options than styrofoam. If you use styrofoam it should be extruded foam not expanded foam (like a cheap drink cooler). It will be blue in colour. It can be coated with epoxie resin to seal the surface and make it stronger, then use automotive high build primer to sand to a polished finish. Then the surface needs to be waxed with a mould release wax and buffed. There needs to be a positive "draft" on all the verticle surfaces to get the plaster
parts out. If you want to use polyester resin you can machine your moulds out of PVC foam which is usually yellow in colour. I use 3/8" core box router bits from Heleta to get filleted corners in my foundry patterns. The suggestion above of the red rubber mould seems like a good idea to me. You would machine the positive and coat it with the liquid rubber. Should be easy to separate from the plaster. If useing a rigid mould blow compressed air between the mould and part to free it up.
wizzardworks

Line the Styrofoam with tin foil and spray with PAM cooking spray as a release agent. Now pour in plaster.

Maybe you could make the styrofoam part smaller than you need & then cover that with clay or plaster to build it up to the size & shape you need for you final buck size.

There's a couple of forums for making costumes like storm trooper armour & such, but they have a lot of good information on vacuum forming. Try goggling TK560 & theRPF. I found a lot of good information over there. When I was getting into vacuum forming.

If you already do vacuum forming, why not form some thin plastic over the styrofoam. They do it in the RC world on jets all the time.

can project styrothane (rigid polyurethane projectable) EPS does not attack hardens in 7 seconds and can be machined.
http://www.futuracoatings.com/pdf/Te...ry/Pdf_941.pdf

Thanks for all the suggestions. I should have given more information in the beginning. The styrofoam insert I want to reproduce belong to a Transformer toy from the 80's. It cost me around $50 for this styrofoam insert. My plan is to reproduce the styrofoam in plastic so it is more affordable.

I have vacuum formed styrofoam like this before and it crushed it.

I looked at this site: "can project styrothane (rigid polyurethane projectable) EPS does not attack hardens in 7 seconds and can be machined." But it requires a sprayer and looks like it could be costly.

I think spraying with to metalize it might be beset. I done this with wood but I am not sure it will dissolve the styrofoam.

I might try and use foil or cern wrap and then poor plastic in the styrofoam.

I would like to find somebody with a copy carver or wood duplicator and have them make a wood mold.

Any other suggestions.