It is easy to find pictures of spalling bricks at google. This happens because water trapped in the pores of ceramic and concrete expands during freezing and breaks it down. This should be a concern to people making architectural and sculpture pieces for outdoors. How do you know if your ceramic will spall? It needs open and closed pore space if over 1% closed porosity. Measure the percentage gain in weight (of a test tile) after a 24-hour water soak, that is 'open porosity'. Then boil for 5 hours and it will soak up more water, measure that as the % closed porosity. The second number needs to be 20% greater than the first. Why? The closed space provides a place for expansion as the water is freezing.
Outdoor Weather Resistant Ceramics
How can you be sure that the porosity of your fired ceramic ware is low enough to prevent freeze-thaw breakdown in the winter?
In ceramics, clays with added aggregate are free formed or molding into shapes that are slowly dried and fired in a kiln. The process requires much skill.
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