Creosote is a highly flammable tar residue that can form when wood is burned incompletely. A smoky fire without enough oxygen or a malfunctioning stove can increase the opportunity for creosote buildup. There are several forms of creosote buildup: the first, a fine, dusty soot that can be cleaned very easily; the second, a grainy black soot that can be cleaned fairly easily with a chimney brush; the third; a thick, tar-like buildup that is more difficult to remove and requires special tools; and the fourth, a shiny, glazed coating that is the most difficult to remove. If your chimney technician finds a creosote buildup even one-eighth of an inch thick or with a glazed coating, it’s time for a cleaning as soon as possible.
Mortar Joint Cracking
Mortar is porous, allowing it to absorb water. Over time and with the addition of freezing temperatures, water can expand in the mortar until the joints become cracked, often with chunks of mortar falling out completely.