Smooth-Cast ONYX SLOW
Black casting resin, 100A:100B · US · not yet reviewed
How long before you can demold Smooth-On Smooth-Cast ONYX SLOW?
Short answer
Project stage ladder
Demolding, handling, finishing and final use may occur at different times
For mold making and casting, identify which stage the stated to demold 90 minutes milestone actually unlocks. Earlier handling does not prove final cure.
Calculate the next project stage
Your countdown
Stated times
- Working time ends5 minutes
- Ready to demold90 minutes
From Smooth-On product page · checked 2026-10-25. Anything not listed isn’t stated by the manufacturer.
Manufacturer website: smooth-on.com
Conditions & fine print
- Stated conditions: 73°F (23°C)
- Smooth-On says to store and use material at 73°F (23°C), that warmer temperatures reduce working and cure time, and not to cure rubber below 65°F (18°C). Mild heat of 150°F can speed curing. Post-cure is optional (1 hour at room temperature, then 4-6 hours at 250°F).
- Region US. Formulas can differ between countries; check your container.
- Working time ends: At 73°F (23°C); depends on mass and mold
- Ready to demold: At 73°F (23°C); depends on mass and mold
- Entered from the manufacturer source; second review pending. Report outdated information
- Actual results depend on preparation, thickness, ventilation, temperature, humidity, mixing and substrate.
Using this specific product
Smooth-On Smooth-Cast ONYX SLOW is listed here as the Black casting resin, 100A:100B version for mold making and casting. For casting resin, the useful question is not simply whether the surface looks finished—it is whether the exact next-action milestone shown above has been reached.
Before you start
- Confirm the package says Black casting resin, 100A:100B; related versions can use different timing.
- For mold making and casting, pay particular attention to accurate mixing, mold material, mass and room temperature.
- At 73°F (23°C); depends on mass and mold.
How to check readiness
Check the casting itself for flex or tack before demolding. Pot life: 5 minutes. Flex the mold away at one edge and stop if the casting bends, tears or remains tacky.
Avoid this mistake
Demold time is not necessarily full mechanical cure.
Questions
How long before you can demold this product?
Smooth-On states: Pot life: 5 minutes. Conditions: At 73°F (23°C); depends on mass and mold. Cure time: 90 minutes. Demold time depends on mass and mold configuration. Conditions: At 73°F (23°C); depends on mass and mold. These are the manufacturer’s stated times, not a guarantee.
How long do I have to work with this product?
Smooth-On states: Pot life: 5 minutes. Conditions: At 73°F (23°C); depends on mass and mold. These are the manufacturer’s stated times, not a guarantee.
What affects how long this product takes to dry or cure?
Smooth-On says to store and use material at 73°F (23°C), that warmer temperatures reduce working and cure time, and not to cure rubber below 65°F (18°C). Mild heat of 150°F can speed curing. Post-cure is optional (1 hour at room temperature, then 4-6 hours at 250°F). Follow the product label for your conditions.