A chimney’s prime function is to divert smoke up and out of your home; however, if the inside or outside walls crack, this could cause it to work incorrectly. If cracks are noticed by you or a professional during regular inspections, chimney repair is necessary before the chimney should be used again.
What Can Cause Chimney Cracks?
Improper Construction
During the construction of the chimney if an air space is not left between the flue line and masonry chimney sides, it can cause the surrounding brick to crack as the flue heats up and expands.
Also, if a chimney is set on a defective footing or foundation or was not properly secured to the building, it could result in the chimney leaning, or curling. This tends to lead to cracks in the mortar joints.
Water Leaks
If a chimney has a missing or faulty chimney cap, defective flashing, or open-mortar joints, water can leak into the structure. This trapped water then freezes during the winter causing the masonry or flue liner to expand and possibly crack. This is usually the most common explanation for cracks appearing in a chimney.
Location
Chimneys, unlike house frames, are not built to move. So, if your home is in an area susceptible to earthquakes, it is wise to get an inspection after each quake to ensure your chimney is still safe to use.
How to Know if a Chimney Repair Is Needed?
Each year after you quit using your chimney and fireplace, it is a wise idea to call a chimney sweep for a cleaning and inspection. During the inspection, they should look for cracks on the inside and out of your chimney and notify you if they see any. It is important to have any noticeable cracks repaired as soon as possible. Small cracks can and will get bigger, and they can lead to an inefficient and unsafe chimney.
Resources: InspectAPedia®, How Stuff Works