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How to Use Silicone Caulk as a Casting Material

Updated February 21, 2017

Silicone is a rubber product that is used to cast many objects out of moulds. Typically this process uses Room Temperature Vulcanization (RTV) silicones, which uses a chemical reaction to cure the rubber. These products are often expensive, however, and must be ordered from speciality companies. It is possible to produce the same objects using silicone caulking from the hardware store. This process requires more time and labour, but is a much less expensive alternative for the occasional hobbyist.

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  1. Prepare the mould with a release agent. If the mould is a rigid material such as cement, fibreglass or plastic, brush on a thin layer of petroleum jelly. For flexible moulds such as silicone, latex or urethane, brush on a layer of hand soap. Buff out the excess with a paper towel once it has dried.

  2. Load a tube of 100 per cent silicone caulk into a caulk gun and cut the tip off with a sharp pair of scissors.

  3. Squeeze a small amount of silicone into the mould.

  4. Spread the silicone over the entire mould surface with an acid brush, available at most art and hobby stores. Brush silicone into any recessed areas of detail. Work gently to avoid introducing any air bubbles into the silicone.

  5. Add more silicone as needed until the first layer is 1/4-inch thick.

  6. Allow the silicone to air dry. This could take up to 24 hours depending on the brand.

  7. Add a second layer of silicone to the first, following the same procedure as the first. Allow the second layer to air dry.

  8. Continue adding layers of silicone until you achieve the desired thickness.

  9. Remove the silicone casting from the mould once it has completely dried.

  10. Warning

    Do not apply silicone thicker than 1/4-inch at a time. Because it is an air-dry product, applications that are too thick will form a skin that prevents the interior from drying.

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Things You'll Need

  • Mold
  • Petroleum jelly or hand soap
  • Brush
  • Paper towel
  • 100% silicone caulking
  • Caulk gun
  • Scissors
  • Acid brushes

About the Author

Alex Smith began writing in 2006 and brings a combination of education and humor to various websites. He holds a Master of Arts in theater and works as a professional makeup and special-effects artist.

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