Home / Chimney Academy / Spalling Brick and Freeze Damage
Spalling Brick on a Chimney: Causes, Freeze Damage and Repair Options
When the face of a brick flakes, pits or pops off, the brick is telling you that water has been getting in. Here is what spalling is, why freezing weather makes it worse, and how it is usually repaired.
What spalling looks like
Spalling is when the surface of a brick or stone breaks away in flakes or chips, leaving a rough, pitted or crumbled patch. On a chimney you may see small pieces of brick face on the roof, in the gutters or on the ground below, or bricks whose outer skin has peeled off and left a darker, softer surface.
Home-inspection training material notes that spalling may be only cosmetic. Even so, it is a symptom, not the problem itself: it points to moisture and pressure inside the masonry.
Why it happens: water, freezing and salts
Brick is porous. The Brick Industry Association explains that this porous structure lets brick move water, and that rain is the main source of moisture in masonry. Two things then tend to follow:
- Freeze-thaw cycles. Inspection training material lists freeze-thaw cycles in water-saturated materials as one cause of spalling. Water that has soaked into a brick expands when it freezes, and repeated cycles can break the surface away.
- Salt crystals. The Brick Industry Association notes that salts which crystallize inside masonry can develop strong pressures and may cause brick to spall. The white powder you sometimes see on the outside is covered in our guide to white stains on chimney brick.
A chimney is exposed on all sides and has no roof over it, so the source of the water matters. Common entry points are a cracked or crumbling crown, a missing or damaged cap, failed flashing and open mortar joints. See crown repair vs replacement and why is my chimney leaking.
What a professional checks
- How widespread the damage is: a few bricks, one face of the chimney, or the whole top section.
- Whether the mortar joints around the damaged bricks are open or soft. Inspection training material treats mortar that crumbles when poked as a warning sign.
- Where the water is coming from: crown, cap, flashing, joints, or a combination.
- Whether the spalled bricks are still sound enough to stay, or are loose.
A chimney inspection covers the exterior and the interior; the levels are explained in chimney inspection levels 1, 2 and 3.
Repair options
| Situation | Typical approach | Learn more |
|---|---|---|
| A few spalled bricks, sound surroundings | Replace the damaged bricks and repoint the surrounding joints | Masonry repointing |
| Open or crumbling mortar joints | Repoint with mortar of similar composition to the original, since a significantly different mortar can cause damage | Chimney repair |
| Cracked crown or failed cap letting water in | Repair or replace the part that is letting water in | Crown repair, caps |
| Widespread damage across the chimney | Partial or full rebuild of the affected section | Partial vs full rebuild |
Fixing the water source is as important as replacing the bricks. Otherwise the new masonry faces the same conditions. Water repellent treatments can be part of the plan; see chimney waterproofing. The Brick Industry Association cautions that coatings alone are not recommended to treat salt problems, since they can trap water and salts just under the surface, so a coating is not a substitute for repair.
Safety note: Falling brick can injure people below. If pieces are coming off, keep people and pets away from the base of the chimney. Do not climb onto the roof to inspect or patch it yourself.
When to act
If you notice flaking brick, loose pieces, or damp stains inside near the chimney, book an inspection before the next winter. Our Rumson project is an example of crown and masonry repair work.
Frequently asked questions
Is spalling always serious?
Not always. Light surface flaking can be cosmetic. But it shows that moisture is reaching the brick, so it is worth finding out why.
Can spalled brick be painted or sealed over?
A coating on its own does not fix the cause and, according to the Brick Industry Association, can trap water and salts below the surface. Repair the damage and the water entry first.
Does freezing weather cause it every winter?
Freeze-thaw damage needs water in the brick when it freezes. A chimney that stays dry is much less likely to be affected, which is why the crown, cap and joints matter.
Do I need to rebuild the chimney?
Not necessarily. The right scope depends on how widespread the damage is. See chimney repair vs rebuilding.
Next step
Request an inspection or call (862) 225-6529. AM Chimney Sweep is a registered (NJ HIC #13VH14312300) and insured New Jersey home improvement contractor.
Sources
- Brick Industry Association, Technical Notes 23A: Efflorescence (brick porosity, rain as main moisture source, salt crystallization and spalling, coatings trapping water and salts)
- InterNACHI, Inspecting Visible Masonry (spalling described, professional assessment, repointing with similar mortar, mortar deterioration where moisture is excessive)
- InterNACHI, How to Inspect Fireplaces, Stoves, and Chimneys (freeze-thaw and osmotic pressure as causes of spalling, crumbling mortar as warning sign)