Chimney Cracks, and What They Mean For Your Home

Cracking masonry is among the most common symptoms of a damaged chimney, frequently caused by severe temperature changes that build up moisture and make the masonry brittle.
A chimney with a bad split before repair in London, ON

A homeowner shouldn’t be surprised when they find that over the years, their chimney has cracked. It’s understood that the masonry of a chimney can last for generations, but between wind, moisture, and the quality of the initial build, it’s almost certain that the structure will experience weathering. This damage can come in many forms:

  • Deteriorating Brick
  • Structural Weakness
  • Chimney cracks and Leaks

Is a cracked chimney dangerous?

Cracking masonry is among the most common symptoms of a damaged chimney, frequently caused by severe temperature changes that build up moisture and make the masonry brittle. This is called a ‘freeze and thaw’ cycle. More than just the mortar joints can crack; the chimney cap and inner liner can fall victim to the same fracturing, creating leaks that could:

  • Weaken the overall structure
  • Cause water damage
  • Encourage the growth of mold

All of these pose a significant problem to more than just your chimney, putting your home and potentially other nearby buildings in danger. Obviously the biggest concern would be your chimney cracking to the point where it will no longer stand, but the additional risks of water damage and mold could create long lasting problems. These are issues that require professional help that is larger in scope and far more intrusive: and therefore expensive.

How do i fix cracks in my chimney?

The process of fixing a cracked chimney can vary depending on how much weathering has occurred, and in the same way can be more or less complicated. A homeowner shouldn’t feel obligated to maintain the structure of their chimney all on their own: for some jobs, it’s not only safer but smarter to bring in a professional. If you notice damage that is:

  • Structurally significant,
  • High off the ground,
  • Causing problems in other areas of the home (ie leaks),

then the best course of action is to call a professional. This will prevent the risk of serious injury or even death to the homeowner. Besides serious damage repair, however, a professional will also take on small-scale repointing that will both maintain your chimney and the aesthetic of your home or building.

Preparing for a job

There are a few considerations that need to be made before repairs can begin on your chimney. There are obvious preparations to make, such as:


Type of mortar

The type of mortar used is important to the structural integrity of the chimney. You want the mortar to accommodate the expansion and contraction of the brick itself, to prevent future chimney cracks. Besides structural concerns, discerning homeowners may want to exactly match the colour of the patched mortar to that of the existing masonry.


Ease of access

Access is important for masonry work, as well as keeping the work area clear and open. Access dictates the route the mason will take to and from the worksite, and where materials will be brought in from. The area around your home or building will need to be completely cleared to make room for the chimney crack repair.



The season is also a vital consideration for masonry work. In order for the mortar to set properly in colder temperatures, the work area needs to be adjusted. Tarps need to be set up around the drying mortar, with gas heaters running and exhaust ports to prevent suffocation for the workers inside the area. This allows the mortar to set properly and prevent cracks during the ‘freeze and thaw’ cycle. In the summer, mortar should be prevented from drying out too quickly by dampening the areas of application.

Working on the chimney

Depending on where the damage is located, the repair will have to run differently. If the crack is closer to the top of the chimney, a mason must adhere to ‘Working at Heights’ training practices to safely transport workers and materials to the site. 

Work must also be done with special harness systems that allow masons to navigate the height freely and with minimal hazard. Even when just repairing chimney cracks, mortar must be mixed on the ground (for safety, depending on the roof, and to prevent splashing on the building itself).

Mixing the mortar also affects how the repaired chimney will look: a professional is best when trying to match colours with the undamaged sections of mortar. A mason would also know best which type of mortar is the best for the structural security of your chimney, and how to effectively apply it.

How is the crack repaired?

The process isn’t always the same, but with a standard crack repair, the mason will use a mortar raking tool to remove the damaged portion of mortar. This kicks up dust and should be done with the proper safety equipment, such as:

  • Safety Goggles
  • Safety Gloves
  • Face Mask or Ventilation Mask
  • Soundproof Earmuffs

Once the mortar has been ‘chased’ or sanded down to remove the cracked mortar, excess dust must be cleaned from the spaces between the bricks. When the area is clean, replacement mortar will be mixed and applied with a pointing trowel to the vacant spot. There are a couple things to remember about the mortaring process, including:

  • Mortar must be placed all the way to the back of the ‘chase’ (the space between bricks that needs to be filled) to ensure the structural integrity of the bricks
  • For the aesthetic quality of the portion being repaired, mortar must be smoothed down;
  • Avoid getting mortar directly on the face of the brick.

At different stages of the drying process, the mortar may be gently scraped with the edge of the trowel to get rid of edges where the old mortar meets the new, or where the mortar overhangs the brick. When the mortar dries, be sure to brush it down to remove excess dust and edges.

You're not alone

If this task sounds daunting, then you understand why so many homeowners seek out professional masons to repair chimney cracks. The damage that could be wrought by a crack is immense, even if the damage doesn’t occur all at once or even right away. For the longevity and security of your chimney, and the structural integrity of your home down the line, don’t hesitate to call a professional mason for a quote.

author avatar
Matt Lancaster


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