Part 2 of the silicon rubber mold-making series. Content restored — see the full mold-making guide.

Frequently Asked Questions

What does Silicon Rubber Mold Making Part 2 cover? Part 2 of the Silicon Rubber Mold Making series covers pouring the second half of a two-part block mold — applying mold release between silicone halves, building the second clay dam wall, and pouring the second silicone pour over the first cured half with the master still in place. Correct mold release application between halves is critical: silicone bonds permanently to cured silicone without a release agent barrier.

How is mold release applied between two-part silicone mold halves? After the first silicone half cures and the clay bed is removed, every exposed silicone surface must be coated with Ease Release 200 or petroleum jelly before the second pour. A single missed spot causes permanent bonding between the two halves, ruining the mold. Two thin coats with a brush, ensuring complete coverage of the parting surface and any registration keys, is the standard procedure.

What are registration keys and why are they needed in two-part molds? Registration keys are hemisphere or cylinder shapes pressed into the clay bed at the parting line before the first pour, which create matching lock features in both silicone halves. When the mold is closed for casting, these features ensure the two halves align precisely so the parting line seam is invisible and the mold cavity is correctly centered.

How long does silicone take to cure before the mold can be opened? Most platinum-cure silicones including MoldMax 20 require 16 to 24 hours at room temperature (above 70°F) before the mold can safely be opened and the master removed. Attempting to demold early risks tearing the still-tacky silicone, which creates permanent defects. Cold workshop temperatures slow cure significantly and the mold should be brought to a warm indoor environment to cure.

Further Reading from Authoritative Sources

  • silicone rubber — Wikipedia’s silicone rubber article covers Shore hardness, cure chemistry, and the material properties that determine cure time and the risk of inter-layer bonding in multi-part silicone molds.
  • two-part mold construction — Wikipedia’s Molding (process) article provides authoritative coverage of parting line design, registration features, and mold release principles applied in Part 2 of this series.