Mold Star 15 SLOW 1A:1B Platinum Silicone Rubber - Durable, Low

In this review we look at Mold Star 15 SLOW, a 1A:1B by volume platinum silicone rubber aimed at mold makers who need a durable, low-shrinkage material for repeated casting. The bottom line: this is a reliable, easy-to-mix silicone that saves time by avoiding weighing scales and performs well with a wide range of casting materials. For hobbyists and small studios who want long-lasting soft rubber molds and compatibility with wax, gypsum, resin, concrete, and low-temp metal alloys, Mold Star 15 SLOW earns its place in a mold library.

Key Features

• Simple 1:1 mix: Mixing by volume removes the need for a scale, speeding setup and reducing measurement errors for routine molding work.
• Durable platinum rubber: The cured rubber is tear resistant and designed for long life, so molds hold detail over many casting cycles.
• Wide material compatibility: Suitable for casting wax, gypsum, resins, concrete and low-temperature melt metal alloys, making it a versatile workshop material.
• High heat resistance: Withstands up to 450F (232C) once cured, so it tolerates hotter pours than many common rubbers.
• Low long-term shrinkage: The formulation reduces dimensional change over time, which helps preserve accurate reproductions.
• Practical working times: A 50 minute pot life and roughly 4 hour demold time balance slow cures with reasonable throughput for small batches.

Who It's For

Experienced hobbyists, prop makers, and small studio artisans who need a dependable, soft platinum silicone for repeat casting will find Mold Star 15 SLOW well suited to their workflow. Its 1:1 by volume mix and moderate pot life make it particularly convenient for projects where vacuum degassing is unnecessary.

Those who require very fast turnaround, industrial-scale production, or compatibility with specialty thickeners labeled incompatible with Mold Star (for example THI-VEX) should consider other product grades or consult technical data to ensure the formulation meets specialized needs.

Pros & Cons

Pros

• Easy 1:1 volume mixing eliminates the need for scales and simplifies small-batch work.
• Tear-resistant cured rubber delivers durable molds that retain detail over time.
• High heat tolerance expands casting options to include low-temperature metal alloys.

Cons

• Longer demold time and 50 min pot life mean slower throughput compared with very fast-cure silicones.
• Not compatible with THI-VEX, so some additives and thickening choices are limited.

Specifications

Our Verdict

Mold Star 15 SLOW is a practical choice for artisans who value easy volume mixing, tear resistance and heat tolerance in a soft platinum silicone. It is good value for small studios and hobbyists who cast wax, resins, gypsum, concrete or low-temp metal alloys and want molds that hold detail over many uses, though shop managers needing very fast cycles should evaluate faster-curing alternatives.

Frequently Asked Questions

Can I mix Mold Star 15 SLOW by volume without a scale?
Yes, the product is formulated for a 1A:1B by volume mix so accurate volume measurement is sufficient for proper cure.

Is vacuum degassing required?
Most applications do not require vacuum degassing due to the material's relatively low viscosity, though complex pours may still benefit from degassing.

Can it be used with metal casting?
It is suitable for casting low-temperature melt metal alloys thanks to its cured heat resistance up to 450F (232C).