How do I make a Mold from a Polystyrene (Styrofoam) Shape?

Question

Got a few bits I want to make a master Mold from that are in Polystyrene ant the moment (Not High Impact).

Once I've got the master mold I was gonna use a plaster based to make casts.

Any ideas?

Answer 1

Hey Mickey,

Just cover the Polystyrene shape with your mold material. Leaving an opening at the bottom or back. Then use one of the paint thinners that eats Polystyrene to get it out of there.

But if you make the mold with a seam (to take it apart), that will be needed when you use the mold for real.

These are just thoughts - hope they help you.

Answer 2

just like you would make a mold of any other material.
Clay or plaster comes to mind as cheap mold materials.
Make you mold with your final material in mind. It's pointless to make a one piece mold by dissolving the polystyrene if you then want to make your object in plaster which then you may not get out of your mold without destroying your mold. Introducing parting lines by cutting your mold into pieces usually results in bad alignment due to the lack of keys...

How you make a mold depends a lot on the shape of your object and the material you are going to cast it in. It also depends how many casts you want, as some techniques give you just a single casts others multiple.

If you don't know about mold making take a class or read a couple of books. Books which deal with metal casting techniques usually have a section about mold making as well.

Make sure you know what undercuts, parting lines, mold release, mother mold, and mold keys mean before you make your mold...

Answer 3

Forgive me if this sounds off, but isn't styrofoam porous? Don't you need a silicone mold for plaster?

If not, then all you have to do is carve out the negative image of whatever you're trying to make your mold of so that when you pour the plaster into it, the object will look correctly.

Answer 4

i am using a Styrofoam head and I want to put silicone over the Styrofoam head but I want to reuse the Styrofoam head for other times can't I just put Vaseline over my Styrofoam head and then clay over that if so not sure which kind of clay I should use can anyone help.also what type of silicone should I use?