So, you’ve either built a new home or simply rebuilt your chimney, but now you see cracks. This can be disheartening, especially if you’ve just had the chimney replaced due to structural problems or similar cracks. There are many possible causes to these cracks, but is important to deal with these cracks before water can enter them and either erode away more brick or cause even more damage due to the freeze-thaw process that frequently occurs, especially through winter months.

Why did this even happen in the first place? Even if the chimney is brand new, using brand new brick and mortar, there are various reasons why a chimney would crack. It is important to distinguish between hairline cracks and long cracks that appear to just keep growing. After being laid, brick will shrink from UV exposure and the loss of small amounts of moisture present in brick. This may cause hairline cracks to appear, and although they are not of particular concern, you will want to consider sealing them with a crack sealant.

Conversely, long cracks, either vertical or horizontal, that are wider than what could be considered hairline are of an issue. These will need to be dealt with either by you or a professional. Sometimes the soil is not strong enough to support the extreme weight of a new chimney. Due to this fact the ground will shift. This is called “settling” and can cause cracks to form as the structure is bent ever so slightly this way and that. The settling process can be expected to stop eventually.

Other times, an inadequate footer may be to blame. This slab of concrete is supporting an extreme weight. Your footer must be at least 12 inches thick and extend 15 inches in all directions on the sides of the base of the chimney. Steel bars should be placed 2 to 4 inches up from the bottom of the chimney in both directions for additional support. If the chimney is not placed on a sound foundation, then there can be little hope for a structurally sound chimney. If you suspect that the footer was not properly constructed, then the mason who installed the chimney may be to blame for your chimney woes.

Interestingly enough, mortar does not come to its full strength until it cures completely, a process that can take months in some cases. As the wind blows and the climate changes, the chimney can sway minutely this way and that. As the structure is bent, cracks can occur. The most sound chimney will encompass steel bars that help to keep the chimney as upright as possible, even during the strongest winds, to prevent the brick and mortar alike from shifting until the mortar has time to cure completely.

No matter the reason behind your cracks, they will only continue to worsen if they are not taken care of. It is imperative to waterproof your brick with a sealant that will not only protect the crack itself from water penetration and freeze-thaw damage, but also allow the brick beneath it to breathe. Certain crack sealants are better than others, and doing a bit of research prior to making a purchase will save you trouble in the future. If you hire a professional to help you out, make sure to inquire as to what type of sealant they will be using on your chimney. Taking the time to read reviews on products and coming to a working understanding of what type of chemicals the product is comprised of will let you rest knowing that your chimney has been taken care of with prime products.

Clay Lamb

Clay Lamb is a Cincinnati Chimney Sweep contractor and the executive producer of the YouTube channel, podcast, and blog Ask the Chimney Sweep. He is also an award-winning educator and public speaker in the chimney and fireplace industry.

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Clay Lamb

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