Spalling brick is that flaking, crumbling damage you see on older masonry buildings. Left alone, it gets worse. Fixed early, you can stop the decay. Here’s what causes it and what to do about it.
The Freeze-Thaw Problem
Brick absorbs water. When that water freezes, it expands. The expansion pressure breaks the brick face apart from the inside. Repeat this cycle hundreds of times over winters, and you get spalling – the surface flaking off in layers.
This is why spalling is worse on north-facing walls (less sun to dry them) and near ground level (more exposure to splashing and moisture).
Other Causes
Bad mortar repointing makes things worse. Old lime mortar was softer than the brick, allowing moisture to escape through the joints. Modern Portland cement mortar is harder than old brick. It traps moisture inside, accelerating spalling.
If your house was repointed with the wrong mortar, that might be your main problem.
Improper coatings can also trap moisture. Painting brick or applying non-breathable sealers prevents the brick from drying out naturally.
Fixing the Damage
Lightly spalled brick can sometimes be stabilized with a consolidant – a liquid that soaks in and hardens. This works for surface deterioration but not deep damage.
Severely spalled bricks need replacement. You chisel out the damaged brick, clean the cavity, and install a matching replacement. This is skilled work if you care about aesthetics – finding brick that matches century-old material isn’t easy.
Repoint with appropriate mortar. For old brick, that usually means lime-based mortar that’s softer than the brick itself. This lets moisture escape through the joints rather than through the brick face.
Prevention
Keep water away from the brick. Good drainage, intact flashing, working gutters and downspouts. Address the moisture source, not just the symptom.
If you seal brick, use a breathable water repellent, not a film-forming sealer. The brick needs to dry out, just not soak up bulk water.
Don’t ignore it. Spalling gets progressively worse. A few flaking bricks today becomes structural problems in a decade.
