How to Make Plaster of Paris Molds

Plaster of Paris is a molding material composed of calcium sulfate hemihydrates, calcium carbonate and crystalline silica. By mixing the powder form with water, you can make simple molds to use for small craft projects--with the exception of hand prints. Because the plaster heats up while hardening and my become uncomfortable in the hands, a different type of molding products is best for hand prints. And though children would be understandably attracted to the process of mixing Plaster of Paris, adults are better suited to this task.

Things You'll Need

  • Plaster of Paris
  • Oil or petroleum jelly
  • Two plastic cups
  • Plastic spoon
  • Paper bowl
  • Object to mold
  • Water
  • Modeling clay (optional)
Clay from a plaster mold.
Clay from a plaster mold.

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Step 1

Lubricate the object to be molded with oil or petroleum jelly. Plaster is activated by water and will attach to objects unless a release agent is used. The oil and water won't mix easily, so oil-based lubricants work well as release agents.

Oiling the object to be molded.
Oiling the object to be molded.

Step 2

Place the object to be molded in the paper bowl.

Object in the bowl.
Object in the bowl.

Step 3

Pour plaster into a plastic cup and add water, mixing thoroughly.

Pouring plaster into a disposable cup.
Pouring plaster into a disposable cup.

Step 4

Pour the mixed plaster over the object so that the fattest part of the object is no more than halfway into the plaster (otherwise it won't come out without breaking the plaster).

Step 5

Allow the plaster 30 minutes to harden. Larger pieces may take longer.

Drying the mold.
Drying the mold.

Step 6

Pull the object gently out of the plaster. Where the object was placed, you see a duplicate but opposite mold of the object. Allow the mold to harden completely.

Removing the object.
Removing the object.

Step 7

Use modeling clay or other soft modeling material to press into the mold to capture the shape. The mold can be reused many times if handled carefully.

Using the mold.
Using the mold.

Tips & Warnings

  • Adults should mix plaster to keep the silica away from children.
  • Clean up the area well so that bits of plaster aren't crushed back into powdered forms.
  • Avoid breathing in plaster dust

References

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