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Cure Inhibition In My Casting

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Q: What is "cure inhibition?"

A: Experiencing Inhibition When Casting – Some casting materials are not compatible with some mold rubbers, and will not cure when cast.  For example, an aliphatic urethane resin (such as Smooth-On’s Crystal Clear plastics) will not cure when cast into an addition-cure (platinum) silicone rubber.  The plastic will remain uncured anywhere it touched the rubber.

Common Complaint – Casting Resin Into A Newly Made “Tin” Catalyzed Silicone Mold - Newly made condensation-cure (“tin” catalyst) silicones give off alcohol and water for up to 30 days after the mold is made.  The alcohol will inhibit the cure of some resins.  Remedy:  Place the mold in an oven at 150 F / 60 C for a minimum of 4 hours or 212°F / 100°C for 4 hours to bake off residual alcohol and water.  Let mold cool to room temperature before using.

Minimizing Cure Inhibition – Read the technical data sheet for the products you are using.  It should tell you under what circumstances inhibition would occur and what you can do to prevent it.  For example, applying a sealing agent to a sulfur clay model before applying mold rubber will prevent cure inhibition in most cases.