How to Mold Latex

Written by scott knickelbine
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How to Mold Latex
Halloween masks like this one are often cast from liquid latex. (Jupiterimages/Photos.com/Getty Images)

Latex is based in natural rubber, and is used extensively to cast masks, toys, doll parts, fishing bait and countless other items that need to be flexible. It is less irritating than synthetic casting compounds such as urethane, and is preferred for casting items that will come in contact with the skin. The best approach to casting latex is to use a plaster mould; the pores in the hardened plaster draw liquid away from the latex and help it to cure. A plaster mould also provides a rigid surface from which the cured latex can be peeled away.

Skill level:
Easy

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Things you need

  • Plaster mould
  • Water-based latex casting compound
  • Talcum powder
  • 2-part foam latex
  • Mixing cup
  • Paint brush

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Instructions

  1. 1

    Lay the plaster mould face up on a flat surface. Make sure it is perfectly dry.

  2. 2

    Fill the mould with liquid latex. Do this even if you want the moulded latex to be very thin.

  3. 3

    Allow the latex to cure for at least 12 hours, or until the upper surface of the latex is dry to the touch. The latex will form a thin layer against the mould.

  4. 4

    Demold the latex casting if you want it to be thin (as in a mask). Sprinkle the upper surface of the latex with talcum powder to keep it from sticking to itself, then carefully peel it away from the mould.

  5. 5

    Add a layer of two-part foam rubber if you want the casting to be thicker and more durable. Mix the foam rubber compound according to the manufacturer's directions, and paint a coat of it onto the upper surface of the cured latex. Allow the foam rubber to cure as per the manufacturer's directions. The foam rubber will swell up to about 1/2 inch thick as it cures, and will be completely bonded to the latex. Carefully peel the finished casting away from the mould.

Tips and warnings

  • If you want to create a latex "skin" from a 3D model (such as a plaster bust), you can paint the liquid latex directly onto it. You can then leave the latex skin in place while you paint it.
  • You can paint latex castings with a mixture of latex thinned with water and coloured with pigments or paints.
  • You can purchase plaster moulds for latex ready-made, or you can make your own by applying high-quality mixed plaster to a wax model or a model prepared with mould release.
  • Latex must be cured with porous mould made from plaster or other latex-compatible material. Latex cast in a nonporous mould will not cure properly.
  • Use extreme care when demolding thin latex castings. They can be torn easily, or cut with sharp fingernails.
  • Foam rubber compounds must be mixed precisely to the manufacturer's prescribed ratios or they will not expand and cure properly.

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