· by Michael Blair, Nashville's Masonry
Spalling is the face of a brick breaking away, exposing the softer interior. It is a moisture problem accelerated by freeze-thaw, and it is frequently caused by something someone did to the wall.
The mechanism
Water absorbed into brick expands when it freezes. If it cannot escape — because the mortar is harder than the brick, or the wall has been sealed or painted with an impermeable coating — the pressure breaks the face off.
Once the face is gone the brick absorbs faster, so spalling accelerates on itself.
Common causes here
Hard cement repointing on soft brick. Impermeable paint or sealer applied to a brick wall. A chronic water source such as a leaking gutter or a failed flashing above.
Also brick used below grade or at ground level that was never rated for it, where it wicks moisture from the soil.
- Hard mortar over soft brick
- Sealers or paint that trap moisture
- Leaking gutters and missing flashing
- Sprinklers hitting the wall daily
- Soil or mulch piled against brick
What can be done
The spalled brick itself must be cut out and replaced — there is no way to restore a face. Matching brick on an older Nashville house takes searching, and reclaimed brick is often the answer.
More importantly, the cause has to be removed, or the replacements spall too.
Do not seal brick to fix it
Film-forming sealers are the most common well-intentioned mistake. They trap moisture inside the wall and make spalling worse rather than better.
Where a treatment is genuinely warranted, a breathable penetrating siloxane repellent allows vapor out while reducing liquid absorption. Even then, fixing the water source comes first.