Why Pottery Explodes in the Kiln

A kiln explosion may seem random, but it is almost always caused by preventable issues. In most cases, the problem occurs when internal pressure builds inside the clay faster than the material can release it. Understanding the common causes helps protect your artwork, kiln shelves, and equipment.

Quick takeaway: The most common cause is trapped moisture turning into steam too quickly. Proper drying and a slow early firing schedule prevent most kiln blowups.

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Trapped Moisture and Steam: The Most Common Cause

Most pottery explosions happen because water trapped inside the clay turns into steam before it has enough time to escape.

• The science: Around 212°F (100°C), liquid water changes into steam. Steam expands significantly compared to liquid water, creating internal pressure.

• What goes wrong: If a piece is not completely dry or the kiln heats too quickly, steam pressure can build inside the clay until it cracks or explodes.

Air Pockets and Structural Inconsistencies

Trapped air is often blamed for pottery explosions, but in most cases the real issue is moisture trapped inside those spaces.

• Weak points: Air bubbles, gaps, and poorly joined sections can collect moisture and create pressure points.

• Uneven walls: Thick sections heat and dry slower than thin sections. Uneven heating creates stress that can cause cracks or breakage, especially during bisque firing.

Thermal Shock: Firing Too Quickly

Rapid temperature changes can place significant stress on clay during firing.

• Expansion stress: When the outside of a piece heats faster than the inside, different areas expand at different rates. This creates tension that can lead to cracking or failure.

• Quartz inversion: Around 1063°F, clay undergoes a rapid structural change. Moving through this temperature range too quickly increases the chance of cracks and damage.

Improper Loading and Poor Ventilation

Kiln loading and airflow have a major effect on how heat and moisture move through the firing chamber.

• Crowding: Pieces placed too closely together can restrict airflow and create areas where moisture cannot escape properly.

• Poor airflow: Without proper ventilation, steam and gases can remain around the ware, increasing the risk of pressure-related failures during early firing stages.

Prevention Checklist

Follow these steps to reduce the risk of pottery explosions, especially during bisque firings.

• Confirm bone dry: Never fire pieces that still contain moisture. If a piece feels cool to the touch, allow additional drying time.

• Use candling or preheating: Hold the kiln around 180°F for several hours to remove remaining moisture before increasing temperature.

• Choose slower firing schedules: Large or thick pieces require slower heating. A slower firing is far less costly than replacing damaged shelves, elements, or kiln parts.

• Build with consistent thickness: Keep walls even whenever possible. For thicker sections, hollow areas or small vent holes can help moisture escape.

• Vent from the beginning: Run a downdraft ventilation system at the start of firing to remove steam and gases as they are released.

Distributor Tip

If a pottery explosion occurs, wait until the kiln has completely cooled before opening and cleaning it. Remove debris carefully from element grooves using a soft brush or HEPA-filtered vacuum. Remaining fragments can cause electrical shorts or accelerate element damage.

Need Help Choosing the Right Firing Schedule?

Tell us your clay body, piece thickness, and kiln model. We can help recommend a safer bisque firing approach.

Why Does Pottery Explode in the Kiln?
Pottery usually explodes because moisture trapped inside the clay turns into expanding steam faster than it can escape. Proper drying, controlled heating, and good kiln airflow are the keys to preventing failures.