Soft washing kills the algae and mould that grow on brick, but it does not remove efflorescence, the white powder that is mineral salt, not growth. Here is how to tell the two apart, what actually removes the salts and whether they come back.
In This Article
What that white powder is
Efflorescence is salt. Water moving through brick and mortar dissolves minerals on the way, and when the water evaporates at the surface it leaves those salts behind as a white, powdery or crystalline crust. It needs three things at once: soluble salts in the masonry, moisture to carry them and a face where the water can dry.
It often shows on new brick while the wall dries out for the first time, and it tends to appear in cool, damp weather when evaporation is slow. It is not alive, so it is not mould.
Look for it where moisture concentrates: at the base of the wall, under window sills, around chimneys, and on garden walls and planters. New brick can bloom more than once as it dries.
Two quick tests before you clean anything
- The dry brush. Rub a small patch with a dry nylon brush. Powder that lifts off as dust is likely salt. Growth smears, stays put or leaves a green or black stain.
- The water test. Wet a small spot. Salt dissolves and seems to vanish, then returns as a pale film when the brick dries. Algae and mould do not do that.
Many walls have both problems. Green algae on the shaded lower courses with white bloom higher up is a common sight.
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Why a soft wash does not fix it
Soft washing is built to kill living things. The cleaning mix works on algae, mould and lichen. Salts are minerals, so there is nothing for the mix to kill. Low-pressure rinse water may dissolve some of the deposit, but it can also carry it deeper, and the salts reappear as the brick dries.
That does not make soft washing useless on brick. It simply has a different target. Think of efflorescence as a moisture symptom and algae as a biological one, and treat each with the tool that fits.
Pressure does not help either. Force can damage mortar joints and soft brick faces, and it drives more water into the wall, which is the opposite of what you want.
What does work, in the right order
- Find the water. Look for overflowing eavestroughs, downspouts that empty against the wall, soil piled above the foundation, sprinklers hitting the brick, cracked mortar and failed flashing. Blocked weep holes matter too, so read our note on weep holes in brick homes.
- Let the wall dry. Efflorescence often fades once the moisture supply stops. Give it weeks of dry weather before you judge.
- Dry-brush the salts off and sweep or vacuum them up. Do this before wetting the wall, so the salts are not dissolved and drawn back in.
- Use a masonry cleaner only if you must. Products made for efflorescence are often mildly acidic. Test a hidden patch, pre-wet the brick, follow the label exactly, rinse thoroughly and keep it off plants. Never let an acid product meet bleach. Old, soft or coloured brick and mortar can etch, so ask a mason first.
- Seal only on advice. A sealer that traps moisture inside brick can make things worse. Ask a masonry specialist which type, if any, suits your wall.
Is it permanent?
The white crust is not permanent. The cause can be. If water keeps moving through the wall, the salts keep coming back, sometimes within a season. Once the source is fixed, efflorescence usually fades and stays gone.
Southern Ontario adds a reason not to shrug it off. Water in brick expands when it freezes, and salts crystallizing near the surface add their own pressure. Over many freeze-thaw winters, persistent moisture can flake the face off the brick, which is called spalling and cannot be washed away.
Call a mason if you see flaking or crumbling brick faces, powdery or missing mortar, damp patches inside the wall or any bulging. Those point to moisture damage deeper than surface salts.
Where soft washing does fit
If the same brick is also green or black in places, soft washing treats that growth once the salts have been brushed off and the wall is dry. When you request a soft washing quote from D&D, mention that you suspect salts as well as growth, so the written scope shows which problem is being treated. Quotes are free and confirmed in writing before work begins. Our brick exterior cleaning guide for Ontario homeowners covers the wider picture.
Key Takeaways
- Efflorescence is mineral salt left behind as water evaporates, so it is not mould and a soft wash cannot kill it.
- A dry nylon brush and a water test help tell salts from algae: salts lift as dust and return as a pale film after wetting.
- Fix the moisture source first, dry-brush the salts, and use a masonry cleaner only after a test patch and per its label.
- The crust is not permanent, but it returns for as long as water keeps moving through the wall.
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