How to Extend the Life of Plaster of Paris


Plaster of Paris is a versatile patching and molding compound that has been used for centuries in construction, medicine and art. Plaster of Paris was named in the 1700's after large deposits of gypsum were discovered near Paris. Now the term is used for any plaster containing gypsum, sand and water. The compound is easy to use, but articles made from Plaster of Paris may easily break. However, there are several ways to strengthen Plaster of Paris to make the medium more permanent.

Things You'll Need

  • Plaster of Paris
  • Water
  • Plastic bucket
  • Measuring cup
  • Spoon or whisk
  • Paper or cloth fibers
  • Other ingredients, depending on method:
  • powdered lime
  • gum arabic
  • bicarbonate of soda (baking soda)
  • soft brush

Cloth or Paper Fiber Method

  • Shred scrap paper finely through a paper shredder or shred fabric (preferably 100% cotton fabric) with a fabric shredder. Pre-cut paper confetti also works fine.

  • Mix 1 ½ cups of shredded paper or fabric to every 8 ½ cups of dry Plaster of Paris.

  • Add water according to package directions. The paper or cloth fiber will strengthen the hardened plaster.

Lime Method

  • Mix powdered lime with water in a large mixing bucket to create "milk of lime" according to directions on the package.

  • Use the spoon or whisk to stir the powdered plaster into the mixture, measuring the dry powder according to package directions.

  • Stir until smooth. The "milk of lime" helps create a harder plaster.

Gum Arabic Method

  • Mix a small amount of gum arabic, available at art or craft supply stores, to water in a large mixing bucket. Whisk well to dissolve the gum arabic thoroughly. One part gum arabic to 100 parts Plaster of Paris by weight will increase the toughness of the finished piece.

  • Slowly add dry plaster, whisking well to create a smooth compound.

  • After achieving the desired thickness, mold plaster as desired.

Bicarbonate of Soda Method

  • This method is used on a piece after it has dried. Mix Plaster of Paris according to package directions and create the plaster piece. Allow to dry thoroughly.

  • Mix a solution of ¼ cup of bicarbonate of soda (baking soda) and 1 cup of warm water. Stir to dissolve the soda in the water.

  • After the Plaster of Paris cast or piece is dry, brush the solution over the finished piece 3 to 5 times, allowing drying time between. The soda solution will increase hardness.

Tips & Warnings

  • Remember that Plaster of Paris becomes quite hot as it dries. Do not cast on skin. Severe burns have occurred using Plaster of Paris on the skin. Instead seek specific casting compounds specifically made for life-casting. These are available in art supply stores and mail order catalogs where sculpting supplies are sold.

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