Grog Addition Calculator
Clay & Shrinkage
claycalc.com
Grog Addition Calculator
Calculate how much grog to add to reduce clay body shrinkage to a target percentage.
Reviewed by ClayCalc Editorial · Updated
Results
Enter your measurements above and click Calculate.
What Is Grog?
Grog is pre-fired, crushed ceramic material that is added to a clay body to reduce shrinkage, improve thermal shock resistance, and provide texture. Because grog is already fired, it does not shrink during the firing process — adding it effectively "dilutes" the shrinkable clay matrix.
The Math Behind Grog Addition
The calculator uses a dilution model: the blended shrinkage is approximately equal to the clay shrinkage multiplied by the clay fraction in the mix. To achieve a target shrinkage:
grog_fraction = current_shrinkage / target_shrinkage − 1
grog_pct = grog_fraction / (1 + grog_fraction) × 100
Mesh Size Guide
| Mesh | Particle Size | Best Use |
|---|---|---|
| Fine (60–80) | Very small | Throwing, tableware, surfaces that will be glazed |
| Medium (30–60) | General | All-purpose hand building, raku bodies |
| Coarse (10–30) | Visible texture | Sculpture, wood-fire, anagama, large pieces |
Method & review note
About this calculation
Uses measured dimensions or weights and a stated arithmetic model. Clay and forming method vary, so production decisions should use test pieces from the actual body and firing.
Reference: Digitalfire — Drying Shrinkage. See the editorial methodology for testing, precision and corrections.
Input handling: Values are sent to the ClayCalc server for this request and are not written to the application database.