Chimneys extend high above the roofline of most homes. The brick on the portion of the chimney extending up has no protection whatsoever. There is nothing shielding it from the driving winds and rains that fall. Since there is no protection for the brick above the roofline, the difference in levels of deterioration between the brick above and below the roofline is often quite noticeable. As your home ages it will quickly become apparent that your chimney brick is in worse shape than any of your other brick.

Rainfall soaks the brick on your chimney, and if the climate you live in experiences any freezing weather throughout the year, you can certainly count on some freezing and thawing damage to the brick. Moisture that seeps into the brick from rainfall, snowfall, or even just vapors in the air will expand and contract significantly enough to cause cracks that will worsen with each new freezing and thawing cycle. Remember that brick has a small percentage of moisture that occurs naturally. This moisture needs to be able to exit the brick freely to prevent spalling (the face of the brick popping off). If you decide to water proof your chimney, it is imperative to use a product that will form a semi permeable membrane over the brick such that vapors naturally occurring inside the brick will not become trapped inside, which would set the stage for spalling to occur.

The crown of a chimney is another area that is particularly susceptible to damage, especially since most crowns are constructed improperly. A mortar crown will not even come close to having the same strength as a crown made from concrete. Sometimes, bricklayers will construct a crown improperly due to lack of knowledge, but under no circumstances should a crown be a simple layer of mortar on the top of a chimney. Cracks will almost certainly appear and require repair.

Concrete is made of cement, stones, sand, and water. Stones in this concoction add strength incomparable to a crown made of mortar alone. Concrete should be the material that your crown is structured from. Similarly, if an expansion space between the crown and the flue liner is not left, cracks are, again, almost certain to occur. As the moisture present in the crown expands and contracts the crown needs room to expand and contract as well. If no expansion joint is left, the pressure that builds will cause cracks to occur.