Guide · Weather
How Missouri Freeze-Thaw Cycles Damage Brick and Mortar
Brick and mortar absorb water. When that water freezes, it expands, and eastern Missouri winters repeat that cycle again and again.
How freeze-thaw works
Brick, mortar, and stone are porous. Rain and melting snow soak in, and when the temperature drops below freezing, that water turns to ice and expands. When it thaws, more water gets into the space the ice opened up. Each cycle widens cracks a little more.
Winters in eastern Missouri often swing above and below freezing many times, so masonry here goes through a lot of these cycles.
Where damage shows up first
Chimney tops
The most exposed masonry on the house, see chimney repair.
Wall caps and ledges
Horizontal surfaces hold water.
Steps and stoops
Snow, standing water, and de-icing salt.
Below downspouts
Concentrated water on the same few bricks.
Retaining walls
Saturated soil freezing at the base, see retaining walls.
Sprinkler zones
Walls wetted every day all summer go into winter damp.
Signs after winter
- Brick faces flaking or popping off (spalling)
- New cracks or wider cracks in mortar
- Sandy grit at the base of walls
- White efflorescence staining
- Crown cracks on the chimney
Why the wrong mortar makes it worse
Mortar should be the weaker, more breathable part of the wall so moisture can escape through the joints. When a wall is repointed with mortar harder than the brick, water has to leave through the brick instead, and that’s where freeze-thaw does its damage.
That’s why mortar matching matters in tuckpointing, especially on older brick.
How to reduce freeze-thaw damage
- Clean gutters before winter and extend downspouts away from walls
- Keep sprinklers off brick
- Grade soil away from the foundation
- Fix chimney crowns and wall caps before winter
- Use sand, not de-icing salt, on masonry steps
- Avoid sealing brick with non-breathable coatings
When to repair
Spring is the time to inspect and fall is the time to fix, so repairs cure before the next winter. Mortar work shouldn’t be done below about 40°F. If you spot damage, see masonry & brick repair.
More guides
Can You Fix Brick Mortar Yourself? When DIY Works and When It Doesn't
When a small DIY mortar repair makes sense, how to do it properly, and when it’s time to call a mason.
Masonry Repair vs. Restoration: Which Does Your Home Need?
Two different kinds of project. How to tell which your home needs, and what each involves.
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