Cure inhibition occurs when a surface contaminant prevents a material from curing as expected.

Experiencing Inhibition When Making a Mold

When making a mould, cure inhibition occurs when contaminants on a model's surface prevent the liquid mould rubber from curing correctly. While the cured rubber mould may appear fine, you will discover that inhibition occurred at the interface between the rubber and the model's surface. The rubber will be sticky and not fully cured.

For instance, applying latex, urethane, or silicone rubber directly over a model made of clay containing sulfur will result in cure inhibition. The sulfur in the clay prevents the rubber from curing. The rubber may seem fine on the outside, but anywhere the rubber touched the clay, it remains sticky and will never cure.

Remedy: Apply an appropriate sealer.

Note that in some cases (especially with platinum silicone like our Mold Star® Series), a sealer will not prevent cure inhibition. In such cases, you might want to consider our Inhibit X surface treatment.

Inhibition from Sealing Agents

Not allowing a sealing agent to dry or allowing enough time for it to "flash off" before applying a release agent or mixing and applying mould rubber over your model can lead to cure inhibition.

Remedy: After applying the required number of coats, let your sealing agent dry thoroughly (30 minutes should suffice) before applying a release agent (if necessary) or mould rubber.

Please note: Humidity will affect the evaporation rate of solvents. The more humid the environment, the longer it will take for a sealer or sealer/release combination to dry. In highly humid environments (80+% RH), these solvents can take a couple of days to dry or may never dry, depending on the solvent.

Additionally, if you use a solvent-based sealer such as shellac or acrylic and then apply a liquid release agent on top of that, the solvent in the liquid release may "re-liquify" the shellac or acrylic, and additional time is necessary to allow everything to dry.

Applying Rubber Into/Over Rubber

Some mould rubbers are not compatible with others. For example, condensation cure silicones will not cure when applied against an addition cure silicone, and vice versa.

Remedy: Read the technical data sheet for the products you are using. It should inform you under what circumstances inhibition would occur and what steps you can take to prevent it.