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How to Strengthen Plaster

Updated February 21, 2017

Plaster is a compound made from gypsum, sand and water. It has been used since ancient times for construction and artistic purposes. Plaster can be a versatile medium, and is often used for making statuary from a mould. When using plaster for these purposes, however, it can also be brittle and break easily. Paper, lime powder, gum Arabic and sodium bicarbonate can all be used as strengtheners for plaster.

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  1. Shred scrap paper finely by passing it through a paper shredder. Pre-cut paper confetti can also be used.

  2. Mix 1 1/2 cups shredded paper or fabric to 8 1/2 cups plaster of Paris, which is dry.

  3. Add water to this mix in the amounts proscribed on the package of plaster.

  4. Follow the package directions on mixing the plaster. The paper or cloth fibre will help strengthen the hardened plaster.

  5. Add powdered lime to water to create "milk of lime." Use the amounts dictated on the powdered lime package. Mix this in a large bowl or bucket.

  6. Mix the powdered plaster into the lime in the amounts directed by the plaster package. The amount of milk of lime to plaster should be the same amount of water to plaster as directed on the package.

  7. Use a spoon to stir until smooth. This will create a harder plaster.

  8. Mix a small amount of gum Arabic to water. Use a large mixing bucket.

  9. Whisk the mix well in order to dissolve the gum Arabic thoroughly.

  10. Add 1 part gum Arabic to 100 parts plaster of Paris by weight. This helps increase the toughness of the plaster.

  11. Create the desired plaster. Mix according to directions, and create your moulds or whatever purpose you have in mind for the plaster.

  12. Allow it to dry thoroughly.

  13. Mix 1/4 cup bicarbonate of soda to 1 cup warm water.

  14. Stir well in order to dissolve the soda in the water.

  15. Brush this solution over the finished piece. Let the solution dry.

  16. Repeat Step 5 three to five times.

  17. Tip

    Always add dry plaster slowly to a mix and whisk well to create a smooth compound, and to avoid any lump formation.

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Things You'll Need

  • Scrap paper
  • Whisk
  • Paper shredder
  • Plaster of Paris
  • Powdered lime
  • Water
  • Spoon
  • Gum Arabic
  • Mixing bucket
  • Sodium bicarbonate
  • Spoon
  • Paintbrush

About the Author

Darby Stevenson began writing in 1997 for his high-school newspaper, the "Alsea Valley Voice," which won him statewide awards for Best Feature Article and Best Personality Interview. He holds a Bachelor of Arts in international studies and a Bachelor of Arts in religious studies from the University of Oregon.

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