Why do masonry chimneys seem to deteriorate faster than the remainder of the masonry walls?
When masonry chimneys deteriorate quickly, it's often due to poor or deteriorated chimney caps. These caps permit water to enter the top of the masonry wall, resulting in freeze/ thaw deterioration. Once deterioration begins, water readily enters the face of the masonry as well. Deterioration occurs quickly because chimneys experience many large temperature fluctuations. The chimney masonry heats up during use. Then, because it is exposed on four sides, the chimney cools much faster than the remainder of the wall when not in use. These temperature swings increase the number of freeze/thaw cycles. For these reasons, a well-maintained, impervious cap over the chimney top is essential.