Bricks on homes need repaired all the time, however, the bricks on the chimney are exposed to more of the elements than the rest of the home and therefore are often the most damaged bricks on the home. Over the winter, temperatures in most parts of the country dip below freezing and then back up again frequently. Vacillating temperatures are prime for further damage to brick that has any existing damage due to freeze thaw damage.
What is Freeze Thaw Damage?
Freeze thaw damage occurs when water either naturally found in the brick or water that has pooled and is left behind from rain or snow freezes and thaws. When water freezes, it expands. This expansion can cause the brick to crack, or crack further if water is sitting in an existing hairline crack. There is a small percentage of water naturally found in the brick and if these vapors freeze and
thaw repeatedly spalling may occur, which is where the faces of the bricks actually pop off.
Having any cracks on your chimney going into the cold season, you run the risk of these cracks getting even worse. Even hairline cracks run the risk of become a deep, damaging crack, so sealing your cracks with a silicon treatment is a great idea. CrackMagik, a product by ChimneySaver, is a breathable silicon elastomer which can be painted on to cracks or small holes using a paint brush. Sealing these cracks prevents them from worsening over the cold months and causing damage to the point where bricks must be removed and replaced or portions of the chimney must be rebuilt entirely.
After sealing any cracks in the brick or mortar on your chimney using a flexible silicon sealant, it is prudent to waterproof the entire chimney to prevent any new hairline cracks from forming or water damage occurring anywhere else on the chimney. Water repellent selection, especially before a very cold season, is very important. As I already mentioned, there is a certain small percentage of water naturally found in brick, so sealing all of that water vapor inside will actually increase the likelihood of the brick spalling.
Water repellents which form a non-permeable membrane over the brick (meaning that the vapors found inside cannot escape) will actually wind up causing more harm than good in the long run in most cases. I recommend water repellents which penetrate deep into pores of brick, allowing vapor to move out of the brick but water droplets to stay safely on the outside. The type of water repellent you select along with whether or not you deem any existing cracks on the chimney problematic are all serious considerations any homeowner should take prior to the cold season.