What can I do if my clay has frozen?
What can I do if my clay has frozen?
The effect of freezing on clay depends on how deeply it has frozen. In many cases, frozen clay can be recovered with time and preparation.
Light surface freezing
If the clay has only been lightly frosted (freezing limited to the surface), it is unlikely to suffer any lasting damage. Once thawed, it will usually return to a usable state on its own.
Freezing to a depth of around 1 inch
If freezing has penetrated to a depth of approximately 1” (based on a standard 12.5kg bag of clay), the clay should still be recoverable. Once fully thawed, it will need to be thoroughly wedged before use.
Deeper freezing
Clay that has frozen beyond this depth may require significant work to recover, as the water will need to be redistributed evenly throughout the clay.
How long does recovery take?
There is no fixed timescale for recovery once clay has thawed. From our experience, lightly frozen clay typically returns to a usable condition within 4–6 weeks, provided it is stored in a cool (but above-freezing) environment.
Avoid thawing clay too quickly or storing it in a warm area, as rapid thawing can make the clay excessively sticky.
Preventing clay from freezing
Prevention is always better than cure. During cold weather, store clay in a location protected from freezing temperatures.
If clay is stacked together in a large block (for example, on a pallet), freezing is likely to affect only the outer bags—even in severe winter conditions. Covering the stack with insulating material and a tarpaulin will provide additional protection.
The science behind freezing clay
When clay freezes, the water molecules separate from the clay particles. Upon thawing, this can result in clay that feels overly soft or sloppy. Different clay bodies respond differently depending on their composition and particle size.
Coarse clays (e.g. crank and raku clays)
These clays often contain up to 50% non-plastic material (grog), which is unaffected by freezing. The remaining clay minerals are typically fireclays, sometimes combined with ball clay or china clay.
Fireclays have relatively large particle sizes (around 5 microns), making them less susceptible to freeze damage. As a result, most fireclay-based stoneware bodies will thaw and return to a usable consistency with minimal intervention.
Finer stoneware clays
White stoneware and throwing clays generally contain less fireclay and rely more heavily on ball clays (around 1 micron in particle size). During manufacture, these clays are carefully processed to avoid over-blunging—a condition where clay particles become too finely dispersed, resulting in excessive stickiness.
Freezing has a similar effect to over-blunging, breaking apart clay particle clusters and increasing plasticity. These clays usually require more wedging after thawing to restore a workable consistency.
Earthenware clays
Earthenware bodies often contain similar overall clay percentages to coarse stonewares, but the clay minerals are primarily ball clay and china clay. As a result, they tend to react to freezing more like fine stonewares and may require additional preparation after thawing.
Porcelain clays
Porcelain bodies are typically the finest clays produced, with high proportions of highly plastic ball clays and china clays, often with added plasticisers. These clays are usually the most affected by freezing and can require substantial effort to recover.
Further reading (Ceramic Arts Network)>
What about frozen casting slip?
Frozen casting slip rarely returns to a satisfactory condition after thawing. Casting times are often much longer, and cast pieces can be more difficult to handle.
And liquid glazes?
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Dipping glazes usually tolerate freezing well. If the glaze has a high clay content, you may need to add a small amount of water after thawing to restore the correct consistency.
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Brush-on glazes do not always recover well from freezing. The binders and extenders used to improve brushability can be damaged by ice crystals, leading to poor performance.
