Brick, mortar, and concrete absorb water. When it freezes it expands and cracks the masonry, then thaws and seeps deeper. Minneapolis goes through dozens of these cycles each winter, the leading cause of cracked crowns, spalling brick, and open mortar joints.
The freeze-thaw cycle
Water enters porous masonry, freezes, and expands by about nine percent, widening cracks and joints. Repeated cycles each winter compound the damage.
What it damages first
The crown and mortar joints usually go first, then brick faces flake (spalling), then water reaches the liner and framing if left alone.
How to prevent it
Keep water out: a sound cap and crown, sealed flashing, sound mortar, and a breathable masonry waterproofing. Catch small cracks before another winter widens them.
Frequently Asked Questions
Why are Minnesota chimneys so prone to this?
Long winters and many freeze-thaw cycles drive more water damage than milder climates.
Can waterproofing help?
Yes, a breathable sealant slows absorption without trapping moisture.
What does early damage look like?
White staining, hairline crown cracks, and flaking brick.
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