Smooth-On

PMC-121 30 DRY

Urethane rubber · US · manufacturer-sourced

Check your container: This countdown is for the Urethane rubber variant. Similar-looking versions may have different times.

How long before you can demold Smooth-On PMC-121 30 DRY?

Short answer

Ready to demold: 16 hours after application.
Maker & casting resin

Cast-and-demold plan

Gel, demold and full cure are separate days

  1. Mix the Urethane rubber to ratio and pour
  2. Wait for the demold time
  3. Sand or finish after full cure

This product’s stated stages

  • Working time ends30 minutes
  • Demold16 hours

Worth noticing: Working time is only 30 minutes; the next stated stage, demold, is 16 hours.

Common mistake: Demolding early and leaving a soft, tacky casting that never fully hardens.

Maker & casting resin

Project stage ladder

Demolding, handling, finishing and final use may occur at different times

ShapeSetFinishUse

For mold making and casting, identify which stage the stated to demold 16 hours milestone actually unlocks. Earlier handling does not prove final cure.

Time demold and cure

When did you mix and pour?
Conditions that affect drying
Where?
Thickness

Stated times

  • Working time ends30 minutes
  • Ready to demold16 hours

From Smooth-On data sheet · checked 2026-10-25. Anything not listed isn’t stated by the manufacturer.

Manufacturer website: smooth-on.com

Conditions & fine print
  • Stated conditions: Not stated in the data sheet
  • Pot life and cure time shorten in warm rooms and with bigger batches. Follow the current technical bulletin for mix ratio, mixing and release agents. The chart is a summary; read the product's technical bulletin before you pour.
  • Region US. Formulas can differ between countries; check your container.
  • Working time ends: The chart gives no temperature.
  • Ready to demold: The chart gives no temperature; its cure column is the last time value in each row.
  • Entered from the cited manufacturer documentation. Check the current label for the exact formula and region. Report outdated information
  • Actual results depend on preparation, thickness, ventilation, temperature, humidity, mixing and substrate.

Confirm this is your product

Closely named formulas, colors and regional versions can use different times. Match these details to your container before starting a countdown.

Exact listing
Smooth-On PMC-121 30 DRY
Variant
Urethane rubber
Region
US
Listed use
mold making, casting
Timed stages recorded
tooling, demold
Source checked
2026-10-25

Documentation: Technical data sheet · Technical Data Chart (no revision date)

Condition attached to the stated time: The chart gives no temperature.

About this product

PMC-121 30 DRY is a urethane rubber (PMC) on Smooth-On's technical data chart, listed with a pot life of 30 minutes and a cure time of 16 hours. Its pot life is number 8 of 11 from shortest to longest in that comparison. This page uses only the chart values; mix ratio, hardness and release details come from Smooth-On's product bulletin.

Using this specific product

Smooth-On PMC-121 30 DRY is listed here as the Urethane rubber 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 Urethane rubber; related versions can use different timing.
  • For mold making and casting, pay particular attention to accurate mixing, mold material, mass and room temperature.
  • The chart gives no temperature. The chart gives no temperature; its cure column is the last time value in each row.

How to check readiness

Check the casting itself for flex or tack before demolding. The technical data chart gives a pot life of 30 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.

Compare with similar products

Keep going

Questions

How long before you can demold this product?

Smooth-On states: The technical data chart gives a pot life of 30 minutes. Conditions: The chart gives no temperature.. The technical data chart gives a cure time of 16 hours. Conditions: The chart gives no temperature; its cure column is the last time value in each row.. These are the manufacturer’s stated times, not a guarantee.

How does PMC-121 30 DRY compare with others in its line on the chart?

On Smooth-On's technical data chart, PMC-121 30 DRY lists a pot life of 30 minutes and a cure time of 16 hours. Among the 11 PMC rows in this comparison the shortest pot life is PMC-744 (15 minutes) and the longest is PMC-121 30 DRY (30 minutes); cure times run from PMC-121 30 DRY (16 hours) to PMC-780 DRY (48 hours). The chart shows the same pot life and cure time for PMC-121 30 WET, PMC-121 50 WET, PMC-770, so those lines are told apart by hardness and handling, not by timing.

How long after the pot life ends does PMC-121 30 DRY take to cure?

The chart gives a pot life of 30 minutes and a cure time of 16 hours. If the cure clock starts at mixing, that is about 15 hours 30 minutes after the pot life ends. The chart does not state a temperature for these values, so treat that gap as a planning number, not a promise.

How long do I have to work with this product?

Smooth-On states: The technical data chart gives a pot life of 30 minutes. Conditions: The chart gives no temperature.. These are the manufacturer’s stated times, not a guarantee.

What affects how long this product takes to dry or cure?

Pot life and cure time shorten in warm rooms and with bigger batches. Follow the current technical bulletin for mix ratio, mixing and release agents. The chart is a summary; read the product's technical bulletin before you pour. Follow the product label for your conditions.