White powdery deposits on brickwork are one of the most common things we are asked about, and the question is almost always the same: how do I get rid of it, and why does it come back?
The answer to the second part is the important one. Efflorescence is not something that lands on the wall. It comes out of it.
We have covered the equivalent on stone in white powder on your stone. Brick has its own pattern.
What is happening
Bricks and mortar contain soluble salts — some from the clay and the firing, some from the cement in the mortar, some picked up from groundwater or from sand used in the mix.
When water moves through the masonry it dissolves those salts and carries them. The water reaches the outer face and evaporates. The salts cannot evaporate, so they are left behind on the surface as a white crystalline bloom.
So efflorescence is evidence of two things: there are salts in the wall, and water is moving through it and leaving at that face. The deposit itself is harmless. What it tells you may not be.
New brickwork versus old
This distinction decides whether to worry.
New construction efflorescence appears within the first year or two on new brickwork. It is drawing on construction moisture and on the free salts in fresh mortar, and it is expected. It diminishes as the wall dries out and the available salts are exhausted. Brush it off, be patient, and it generally resolves on its own.
Recurring efflorescence on an established wall is different. The construction moisture has long gone. If salt is still arriving at the surface, water is still getting into the wall from somewhere, and that source is worth finding.
Where the water is coming from
On an older Sydney house, almost always one of a short list.
A bridged damp-proof course. Houses of a certain age have a physical DPC a couple of courses above ground. It rarely fails outright, but it is very often bridged — a garden bed built up against the wall, a path or driveway poured above DPC level, render carried down past it, or mulch piled high. Moisture travels around the barrier and up into the wall above.
Blocked subfloor vents. Painted over, paved across, or hidden behind a garden bed. The subfloor stops breathing and moisture goes into the walls instead.
A leak. Efflorescence in one localised patch almost always means something directly above it — a leaking downpipe, a failed gutter joint, a cracked stormwater line, an air conditioner condensate drain discharging against the wall.
Site drainage. Ground falling toward the building rather than away.
Cracked or failed pointing. Open mortar joints let water straight in.
Coastal salt. Near the water, airborne salt deposits on and into the masonry and adds to the load.
The reading that matters
Efflorescence on its own is cosmetic. Efflorescence together with crumbling brick faces is not.
If the brick faces are breaking down, shedding, and leaving orange grit at the base of the wall, the salt is crystallising inside the pores rather than on the surface, and the pressure is destroying the brick. That is fretting, and it is a structural maintenance issue rather than a cleaning one.
We set it out fully in fretting brickwork and rising damp. The headline is that washing a fretting wall accelerates the damage.
Removing it
If the brickwork is sound, removal is straightforward, and the gentlest method is the right one.
Dry brushing first. A stiff bristle brush on a dry wall. Most efflorescence comes off this way, and it is the method least likely to cause problems.
Do this dry, not wet. Wetting it redissolves the salts and carries them back into the brick, where they will reappear in a few weeks. This is the single most common mistake.
Water, sparingly. If brushing is not enough, light water with a brush, then dry the wall as quickly as possible. More water means more salt dissolved and recycled.
Specialist efflorescence removers. Mild acid formulations exist for this and they work. Use them as a last resort, test an inconspicuous area first, pre-wet the wall so the acid does not penetrate deeply, and neutralise and rinse thoroughly afterwards.
What not to use: hydrochloric acid brick cleaner. It is sold for masonry, it is widely misused, and it is counterproductive here. It dissolves lime from the mortar and leaves chloride salts behind in the wall — adding fuel to the exact process you are trying to stop. It also burns the brick face and can permanently change the colour.
Not high pressure. It drives water deep into the masonry, which is the opposite of what you want.
Do not seal it
The intuitive response is to seal the wall so water stops getting in. On brickwork with a salt problem this is the most damaging thing you can do.
Water still enters from the back, from below, through the joints. What the sealer prevents is evaporation from the face. So the water evaporates deeper inside the wall instead, and the salt crystallises there — inside the brick, where the crystal pressure breaks the material apart.
The face may look clean while the brick behind it disintegrates. Masonry needs to breathe, and the same argument applies to sandstone.
The actual fix
Find the water and stop it.
Lower garden beds and paving below the damp-proof course. Clear the subfloor vents. Repair the leaking downpipe or the cracked stormwater line. Establish fall away from the building. Repoint failed joints with a mortar appropriate to the age of the building — lime-based on older brickwork, not modern cement, which is harder than the brick and forces moisture out through the brick face instead of the joint.
Then let the wall dry, which on substantial masonry takes months rather than days, and brush off what continues to appear while it does.
If the wall is sound and simply needs cleaning, see brick cleaning or efflorescence removal. If it is fretting, the useful advice is to deal with the water first, and we will tell you so rather than quote for a wash.
