Freeze–thaw weathering is caused by moisture freezing inside cracks in rock. Upon freezing its volume expands, causing large forces which cracks spall off the outer surface. As this cycle repeats the outer surface repeatedly undergoes spalling, resulting in weathering.
Some stone and masonry surfaces used as building surfaces will absorb moisture at their surface. If exposed to severe freezing conditions, the surface may flake off due to the expansion of the water. This effect can also be seen in terracotta surfaces (even if glazed) if there is an entrance for water at the edges.