DISCOVER
×

How to Make Plaster of Paris Molds

Plaster of Paris is a moulding material composed of calcium sulphate hemihydrates, calcium carbonate and crystalline silica. By mixing the powder form with water, you can make simple moulds 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 moulding 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.

Lubricate the object to be moulded 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.

Place the object to be moulded in the paper bowl.

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

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).

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

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

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

Tip

Adults should mix plaster to keep the silica away from children.

Warning

Clean up the area well so that bits of plaster aren't crushed back into powdered forms. Avoid breathing in plaster dust

Things You'll Need

  • Plaster of Paris
  • Oil or petroleum jelly
  • Two plastic cups
  • Plastic spoon
  • Paper bowl
  • Object to mould
  • Water
  • Modelling clay (optional)
bibliography-icon icon for annotation tool Cite this Article

About the Author

F.R.R. Mallory has been published since 1996, writing books, short stories, articles and essays. She has worked as an architect, restored cars, designed clothing, renovated homes and makes crafts. She is a graduate of the University of California at Berkeley with bachelor's degrees in psychology and English. Her fiction short story "Black Ice" recently won a National Space Society contest.