Plaster For use in slipcast molds.

Plaster is extremely versatile but it is a picky material. This short page will discuss how we use plaster for slipcast moldmaking as part of the Advanced Ceramics Class at TAMU-CC. It is not meant as a complete diescripiton. More complete information can be obtained from plaster manufacturers, books by Donald Frith or by Andy (Andrew?) Martin, or a short Monograph by Richard Notkin.

The plaster itself. Plaster sets through a chemical reaction with water. It can react with the water in air, so plaster should be stored for a minimal amount of time in closed bags. Fresh plaster is essential for making quality molds.

Mixing procedure.

1. Determine amount of water necessary. Ask Louis if you need to. Put a thin laver of vaseline on your hands and on your bucket.
2. Determine the amount of plaster necessary and set it aside.
3. Don your respirator
4. Put the water in your clean greased bucket. Water should be approximately 70 degrees and clean.
5. Note time. Over a three minute interval sift the plaster into the water, preading it evenly over the surface.
6. Let the plaster rest for two minutes. Wash your hands in the plaster wash bucket.
7. Stir plaster with your hand bringing bubbles to the surface. Stir for three minutes.
8. Let the plaster sit until the set begins. Test with finger swipes looking for a prominence at the end of the swipe signalling the transition from being clearly a liquid to having some properties of a solid.
9. Pour into the mold down a ramp incorporateing as little air as possible.
10. Lightly agitate the plaster to cause bubles to rise from the surfact of the mold.
11. Let the plaster alone until at least five minutes after it has become warm and hard. Tricky molds with dificult releases are often best let sit until the next morning.
12. Clean up your area

Mold Soap

Mold soap works to separate palster from plaster and other calcium based materials from plaster. True soaps are necessary. These include, English Crown Mold Soap, Pure Lube (available from Axner Supply), Murphys Oil Soap (from the grocery store) and "Simple Green" also available from the grocery.

Mold soap works by chemical reaction with the plaster form a thin layer of soapscum on the surface of the plaster. It is essential that your mold soap container does not become contaminated with bits of plaster.

Smooth the surface to be mold soaped so that it is free from defects that will create undercuts. Fill small holes if necessary with clay. Make sure you have your keys smooth.

Pour a small amount of mold soap into a small shallow container.

Using a sponge or soft brush work the soap into the surface of the plaster bringing up a lather.Rinse gently with clean water. Repeat three times.

Check the surface. Drops of water should bead up and not be apsorbed into the plaster. If they are mold soap again.