Spalling is the flaking, crumbling, or popping-off of a brick's outer face. In cold climates it is almost always a moisture problem before it is a brick problem: water soaks into the brick, freezes, expands, and forces the surface to break away. By the time the face has spalled, the brick has lost the dense fired skin that kept water out, so it absorbs even more and deteriorates faster. Repair has to address the water path, not just the broken brick.
A spalled masonry face after the outer skin broke away. Photo: Wikimedia Commons (CC).
Confirming it is freeze-thaw spalling
Spalling has several possible causes, and the right repair depends on which one is at work. Common patterns include:
- Freeze-thaw: faces flake near grade, under leaking sills, or anywhere water concentrates.
- Hard-mortar stress: brick spalls along joints that were repointed with an over-strong mortar.
- Salt action: de-icing salt splash near walkways drives surface crystallisation and flaking.
- Wrong brick exposure: interior-grade brick used on an exposed exterior face.
Map where the spalling occurs. Damage clustered low on the wall, below downspouts, or under a failing sill points to a water source you must fix first.
Fix the water first
Replacing brick without correcting the moisture source means the new units will spall too. Trace and repair the leak, drip edge, or drainage problem before any masonry work.
Replacing individual units
Where only scattered bricks have failed, cut-and-replace is the usual approach. Carefully remove the mortar around the damaged unit, take out the brick, and clean the cavity. Set a replacement brick that matches the original in size, density, and exposure rating, bedding it in a mortar compatible with the surrounding wall.
Matching a replacement brick
- Size & coursingMatch existing
- Exposure ratingExterior / severe weathering
- DensitySimilar to original
- Bedding mortarCompatible with wall
Why surface sealers often make it worse
It is tempting to brush a water-repellent or film-forming sealer over a spalling wall. On cold-climate brick this can backfire: a film that blocks the face also traps moisture already inside the wall, and when that water freezes behind a sealed surface it accelerates spalling. Guidance from building-science bodies generally favours keeping masonry able to dry outward, managing where water comes from rather than sealing the face. If a treatment is used at all, a breathable (vapour-permeable) product is the safer category, and only after the moisture source is fixed.
Breathability matters
Masonry needs to dry. Any coating that prevents outward drying risks trapping water where it can freeze and spall the brick from behind.
When to call a professional
Widespread spalling across a large area, spalling combined with bulging or stepped cracking, or damage on a structural masonry wall are signs to bring in a mason or engineer. Those patterns can indicate movement or water problems beyond a single-brick repair.