USG

USG Hydrocal X-21 Gypsum Cement

Casting gypsum cement · US · manufacturer-sourced

Check your container: This countdown is for the Casting gypsum cement variant. Similar-looking versions may have different times.

How long does USG Hydrocal X-21 Gypsum Cement take to dry?

Short answer

Set / hardened: 9–15 minutes after application.
Maker & casting resin

Cast-and-demold plan

Gel, demold and full cure are separate days

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

This product’s stated stages Quoted at 73°F

  • Set9–15 minutes

Worth noticing: The manufacturer states only one timing here (set, 9–15 minutes); nothing else is inferred.

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 casting, sculpture, and molds, identify which stage the stated 9–15 minutes 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

  • Set / hardened9–15 minutes

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

Manufacturer website: usg.com

Conditions & fine print
  • Stated conditions: 73°F (23°C)
  • Gypsum set times depend on water ratio, temperature and mixing. Follow the current USG data sheet.
  • Region US. Formulas can differ between countries; check your container.
  • Set / hardened: At 25 cc.
  • 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 Report outdated information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
USG USG Hydrocal X-21 Gypsum Cement
Variant
Casting gypsum cement
Region
US
Listed use
casting, sculpture, molds
Timed stages recorded
set
Source checked
2026-10-25

Documentation: Technical data sheet · IG2016-USA-ENG/6-17

Condition attached to the stated time: At 25 cc.

About this product

A gypsum cement for casting. The only time on its technical specification is the Vicat set, 9 to 15 minutes for a hand mix at 25 cc. No working time or drying time is given, so it should not be read as a full casting schedule.

Using this specific product

USG USG Hydrocal X-21 Gypsum Cement is listed here as the Casting gypsum cement version for casting, sculpture, and molds. 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 Casting gypsum cement; related versions can use different timing.
  • For casting, sculpture, and molds, pay particular attention to accurate mixing, mold material, mass and room temperature.
  • At 25 cc.

How to check readiness

Check the casting itself for flex or tack before demolding. The technical specifications give a hand-mix Vicat set of 9 to 15 minutes.

Avoid this mistake

Demold time is not necessarily full mechanical cure.

Compare with similar products

Keep going

Questions

How long does this product take to dry?

USG states: The technical specifications give a hand-mix Vicat set of 9 to 15 minutes. Conditions: At 25 cc.. These are the manufacturer’s stated times, not a guarantee.

Does the Hydrocal X-21 sheet give a working time or drying time?

No. The technical specifications list only the hand-mix Vicat set of 9 to 15 minutes at 25 cc.

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

Gypsum set times depend on water ratio, temperature and mixing. Follow the current USG data sheet. Follow the product label for your conditions.