If the faces of your chimney bricks are flaking, pitting, or popping off, that is spalling — and it means water has been getting into the masonry. Caught early it is a simple fix; ignored, it can threaten the whole chimney.
What spalling is
Spalling is when the surface of a brick flakes, chips, crumbles, or pops off. You will often see pieces of brick on the roof or in the yard, and pitted or missing brick faces on the chimney. It is one of the most visible signs of water damage.
Why it happens
Brick is porous and absorbs water. When that water freezes inside the brick, it expands and pushes the face off — the classic freeze-thaw cycle of Midwest winters. Failing mortar joints, a cracked crown, or a missing cap all let in the water that drives spalling.
Why you should not ignore it
- Spalled brick exposes more surface to water, so the damage accelerates
- Enough lost brick weakens the chimney structurally
- Water reaching the interior can damage the liner and firebox
- Left long enough, spalling can require a partial or full rebuild
The fix
Spalled bricks need to be replaced, and — just as important — the source of the water has to be addressed: repointing failed mortar, repairing the crown, adding a cap, and often waterproofing the sound masonry. Caught early, replacing a few bricks and stopping the water is far cheaper than a rebuild.
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Call (708) 432-5330Frequently asked questions
What causes chimney bricks to flake?
Spalling is caused by water absorbed into the brick freezing and expanding, popping off the face. Failing mortar, a cracked crown, or a missing cap let the water in.
Is spalling brick dangerous?
It can become so. As bricks deteriorate, the chimney weakens and water reaches the interior. Early repair prevents a costly rebuild.
Can spalled brick be repaired?
Yes — damaged bricks are replaced and the water source is fixed. Addressing both is essential, or the new brick will spall too.
How do I prevent spalling?
Keep mortar, crown, and cap in good repair, and consider breathable waterproofing to stop water from soaking into the masonry.
Written by Adam Evans, owner of Chimney Sweep Brothers and a chimney technician with 12 years of experience serving La Grange, IL and the western suburbs.