No matter what anyone tells you, there is one thing you should know: Water ruins masonry. To avoid the problems associated with external water penetration of the chimney, the uppermost part of the chimney should overhang the chimney on all sides and be waterproof. Unfortunately, most chimneys built today, do not overhang the chimney on all sides and are not waterproof. This generally causes failure of brick and mortar on the chimney, and can also lead to water staining in the living quarters.