Prevent water penetration and a chimney will last the life of a house; allow water to enter the mortar cracks or brick pores and a chimney will slowly fall apart. 9 out of 10 chimneys show signs of deterioration from water damage. Loose mortar, spalling, cracking and chipping are all signs of neglect. Chimney Seal is unique; designed just for chimneys. The sealer is "breathable" and will not trap water vapor like a traditional sealer would; allowing the structure to break. Without this, damage would occur from the inside out and the brick would expand until it's cracked.