plaster molds

I was looking through the forums and saw a lot of people using WSF for for metals casting and I wondered if you could use it as a master for making a plaster mold? would it need to be sealed first, etc? If anybody has done this let me know. Thanks.

Let me say for a start that I havent cast WSF in plaster - But I have cast a lot of other things. It will need to be sealed and I would suggest the master would need to be smoothed too, plaster likes to stick to rough, porous surfaces.

I believe I've read on the site somewhere that you can't "smooth" the WSF material, because the texture is granular and porous throughout. Maybe another material would work?

You can smooth it quite well after its been infiltrated with a resin.

Can you explain this please? Thx.

Certainly.

Any sufficiently low viscosity clear setting resin will do. Two part thermosets are the cheapest and most readily available. You should be able to buy something that will do the trick at any hardware store.

Just dip the part in the resin, it will infiltrate through the pores in the surface and leave a film on the top that can be easily sanded. Make sure you wipe off excess dripping resin as it cures.

Maybe a brand name or a link? Thanks in advance...

Thank you for explaining.

Sounds like he's talking about polyester resin. If you're looking at a hardware store, this will be sold for fiberglassing. Some craft stores will carry a brand called "Castin' Craft" for doing small scale resin casting*.

Read the package to make sure sure it's a polyester resin. Often you'll find epoxy resins in the same places for the same purpose. Epoxies are stronger than polyesters, but they're also much more viscous (think like honey), and that makes hem unsuitable for what you're doing.

*Polyurethane resins are actually the common standard for casting, not polyesters, and they give much better results. Polyesters are much much easier to use for clear castings though (clear polyurethanes are notoriously temperamental), and are not as expensive. You can find them in hobby shops sometimes, but not usually in craft or hardware stores. Most people I know who use these order them specially online. Still not what you want though- you don't need clear resin for what you're looking to do, but even opaque polyurethanes (which are much more user-friendly than the clear ones) are typically a wee too viscous (about like vegetable oil) for what you're doing.

So go to the Home Depot or whatever, and ask where they keep the fiberglassing materials. Be aware that if you're asking for "polyester resin", they may show you to the auto body filler resins by mistake. These are polyester resins with fillers mixed in to make them thick and paste-like instead of liquid- not what you want. So be sure to be clear you're looking for fiberglassing resin, not auto body resin. Fiberglassing polyester will usually come in a square metal bottle like paint thinner, whereas auto body filler polyester will come in a can like housepaint.

Work outdoors and wear rubber gloves and a respirator when working with resins (a proper canister filter job, not one of those little paper mouth covers) , ALWAYS. Polyester resins contain chemicals which are scary toxic to the central nervous system and bone marrow, so DO NOT breath the fumes, and DO NOT get them on your skin.

If you can't do that for whatever reason, you may want to try soaking you model in an emulsion binder instead of a thermoset resin. Shellac thinned with denatured alcohol will work, as will probably acrylics.