What is the white powder on my brick walls?
It is called efflorescence, and it is not mould, dirt or paint failure. It is mineral salt that has travelled through the wall dissolved in water and been left behind when that water evaporated.
Where it comes from
Bricks and mortar contain soluble salts. Water moving through the wall dissolves them and carries them to the surface.
The water evaporates. The salt does not. What is left is the white crystalline bloom.
This means efflorescence is a symptom. The salt is a nuisance, but the water movement is the actual issue.
Why brushing it off does not work
Brushing removes what has already surfaced. It does nothing about the salt still in the wall or the moisture still moving.
Worse, wetting it with a hose redissolves the salt and carries it back in, where it recrystallises and comes out again next dry spell.
Proper removal uses a neutralising treatment that converts the salt to a soluble form which can be rinsed clear, followed by full neutralisation so no acid residue is left in the brick.
Finding the water source
New builds efflorescence for the first year or two as construction moisture dries out. This is normal and self-limiting.
Persistent efflorescence on an older wall means water is getting in. Common causes: blocked weep holes, garden beds built up above the damp course, a leaking downpipe, or failed flashing.
Cleaning without addressing the source means it returns. We flag what we can see, but a bricklayer or building inspector is the right call for the cause.
Getting the chemistry wrong burns brick
Hydrochloric acid at the wrong strength burns the brick face and leaves it permanently blotchy and lighter.
It also attacks mortar joints, which on an older wall is a real structural concern.
Acid needs to be matched to brick type and fully neutralised afterwards. This is the part that separates a proper job from a bad one, and the damage is not reversible.
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Brick and paver cleaning across Melbourne. Efflorescence, mortar haze, moss and staining removed from brickwork and retaining walls.