Silicon Rubber Mold Making â€” Part 4

Part 4 of the silicon rubber mold-making series. See the full mold-making series.

Frequently Asked Questions

What advanced mold making techniques extend beyond a basic two-part mold? Advanced techniques covered in Part 4 of the mold making series include three-part and four-part molds for masters with undercuts pointing in multiple directions, glove molds using Shore A 10 silicone for extreme undercut situations where block molds would tear, brush-applied silicone techniques for large masters, and core molds for producing hollow castings with consistent wall thickness.

How does a glove mold differ from a block mold? A glove mold builds up a thin (3/16–1/4 inch), highly flexible Shore A 10 silicone skin directly on the master by brush-application in thin layers, backed by a rigid mother mold (fiberglass or plaster bandage). The extreme flexibility allows peeling the mold off masters with undercuts in all directions that would tear any block mold. Glove molds have short production life of 5–20 pieces before tearing.

What registration is required in multi-part mold construction? Each mold part needs registration features that index it against adjacent parts — hemisphere or cylinder shapes pressed into the clay at each parting line to create matching lock features in the silicone. Mold release must be applied between every cured silicone surface before pouring adjacent parts, as silicone bonds to silicone without release agent and any missed surface permanently bonds the parts.

What mother mold materials are used for large silicone mold support? Plaster bandage (Ultracal 30) is easy to work with and adequate for light-duty molds. Fiberglass provides the strongest rigid support for high-production molds and large formats. Urethane rigid foam poured behind the silicone is quick and lightweight but lower precision. All mother mold sections need registration features (bolts through flanges or block key protrusions) for precise alignment.