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Defect · After firing
Spalling
Also called: lime pop
Small chips pop out of the fired surface days or weeks after firing, leaving conical pits.
- Appears at
- After firing
- Severity
- Structural
- How common
- Rare
Causes
Most likely
- ·Calcium compounds (limestone fragments) in the clay body absorbed moisture and expanded
Prevention
- ·Screen clay to remove coarse calcium particles
- ·Use a clay body from a trusted supplier
Can it be fixed?
Not reliably — this one is prevented, not repaired. A cracked or bloated pot is a test tile now.
Related defects
Questions
- Why does spalling happen?
- Most often: Calcium compounds (limestone fragments) in the clay body absorbed moisture and expanded. Other causes: none listed.
- Can spalling be fixed?
- Not reliably once it has happened; the fix is upstream, in prevention.
- How do I prevent spalling?
- Screen clay to remove coarse calcium particles. Use a clay body from a trusted supplier.
Sources. Compiled from Claybench's defect reference — the descriptions, causes and remedies that appear consistently across standard ceramics references and studio practice; no single source. It is the same reference the photo diagnosis tool reasons over. Where the Wikibooks Ceramicware Defects Handbook covers a defect it is linked above.
Not sure which defect you're looking at?
Claybench can read a photo of the pot against this same reference and rank the likely causes for your clay, glaze and firing.