Spalling is a word used to describe a form of masonry or brick deterioration in which exterior portions of the material break away from the surface. This type of deterioration has several causes, including when moisture trapped inside the masonry unit expands and contracts due to freeze/thaw cycles, or by salt crystals wicked into walls when dissolved in water. Spalling may also occur as a result of mortar that is harder that the brick or stones set in it. Any movement in the wall (from vibration, thermal expansion or settling) causes failure in the weaker brick or stone instead of the mortar. For this reason, it is critical when re-pointing a historic masonry wall that a soft lime mortar be used. It is easier to re-point a building than to replace failed bricks or stone.