DIY Urethane Casting


Cast urethane is a two-part epoxy that cures into a hard plastic, similar to PVC. Because cast urethane can capture tiny details of a mold and has such a high tensile strength when hardened, it is often used to prototype machine parts and other components that will eventually be cast in metal or with injection-molded plastic. However, you can do your own urethane casting at home with molds you buy or make yourself.

Things You'll Need

  • Silicone mold
  • Can of urethane mold release
  • 2-part urethane casting resin
  • Clean, dry bucket or container
  • Wooden stick or paint stirring stick
  • Spray the insides of the mold with urethane mold release, and allow it to dry.

  • Add equal amounts of both parts of the casting resin together in a clean, dry container.

  • Mix the resin together, being careful to stir in all parts of the mixing container.

  • Pour the resin into the mold within three minutes of mixing it.

  • Allow the urethane to harden for at least 10 minutes before removing the mold.

Tips & Warnings

  • Items cast in urethane can be painted with plastic-bonding paints, or you can add colorant as you're mixing the resin.
  • You can buy kits to create your own silicone molds, so you can produce very hard, durable replicas of almost anything.
  • Once it's mixed, urethane resin hardens very quickly. Make sure your mold is ready to receive the urethane before you begin to mix the resin.
  • Be sure everything that comes in contact with the urethane resin is completely clean and dry. Small amounts of moisture can cause bubbles to form in the urethane as it's hardening.
  • Ony use urethane with silicone molds. Other kinds of molds -- such as plaster -- can hold trace amounts of water that can ruin the cast item.

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