The white stain test
Four quick things to check on your own wall before you call anyone or buy a harsh cleaner. About two minutes. Answer what you actually see.
Four quick things to check on your own wall before you call anyone or buy a harsh cleaner. About two minutes. Answer what you actually see.
The same test written out, for reading rather than tapping.
Scrub the white area with a dry, stiff brush. What happens?
Spray the white area with a water bottle. What happens?
Run a finger over the deposit. How does it feel?
Look closely at the brick surface under the white stuff.
Harmless salt, but a moisture message
You land here when: Dusts off easily, disappears when wet, thin and powdery, brick face intact.
This is the good one. Efflorescence is just water-soluble salt the moisture leaves behind as it passes through the wall. It does no harm on its own. But it is still telling you water is getting in somewhere, and that is worth solving.
What to do next: Do not power wash it. Find the source of the water first, usually a leaking eavestrough, poor grading against the wall, or a missing chimney cap. Once the water is fixed, the white stops coming back.
Water is getting into the mortar
You land here when: Stuck on hard, does not change when wet, hard and thick or like dripping wax.
That hard, dripping, wax-like white is not surface salt. It is lime being dissolved out of the mortar deep in the wall and carried to the face, where it hardens back into stone. It means concentrated water is getting in, often from a leak directly above.
What to do next: This is a wall telling you water is getting trapped inside it. It usually needs the water source found and fixed, then selective repointing with a proper breathable lime mortar. Do not seal over it.
Trapped moisture is damaging the brick
You land here when: The red face of the brick is flaking, blistering or popping off.
When the brick face itself is flaking, blistering or popping off with the white, the salt is crystallizing just under the skin of the brick and shattering it from the inside. This almost always means moisture is trapped by a sealer or by hard modern cement on a soft old brick.
What to do next: This is a structural warning, not a cleaning job. It usually means selective brick replacement and repointing with a breathable lime mortar, once the trapped-water cause is found. The longer it sits, the more brick you lose.
Your answers point a few directions
You land here when: The answers do not land cleanly on one culprit.
Your answers do not land cleanly on one culprit, which is common. The white on old brick can be a mix, and the safest read comes from actually seeing it.
What to do next: Send a clear photo of the stain and the brick around it. I will tell you which of the three it is and how worried you should be.
This is a guide to help you understand what you are seeing, not a diagnosis of your specific wall. A photo or a visit is how we confirm it.