White powder on brick is one of the most common things owners ask us about, and it's usually not the problem itself. It's evidence. The white deposit is almost always efflorescence: salts that water carried out of the wall and left behind on the surface when it evaporated. Brush it off and it may not come back. If it keeps coming back, the wall is telling you where water is getting in.
How efflorescence forms
Nearly all masonry contains some water-soluble salts. They come from the cement and lime in mortar, from the clay and minerals in the brick, from the backup wall behind it, and from outside sources such as groundwater, de-icing salt and soil.
On its own, salt in a wall does nothing visible. It takes water moving through the masonry to dissolve those salts and carry them toward the surface. When the water reaches the face of the brick and evaporates, the salts are left behind as a white, powdery or fuzzy deposit. The more water moving through the wall, and the longer it keeps moving, the heavier the deposit.
That's why efflorescence tends to show up in cool, damp weather in late fall, winter and early spring. Evaporation is slow, so water has time to carry salts all the way to the surface before it dries. In hot summer weather, the same wall may look clean.
New building bloom
On new brickwork or fresh repointing, a light white haze in the first year is common and normally harmless. It's sometimes called new building bloom. A lot of water goes into a wall during construction, in the mortar and in wet brick, and as that water dries out, it brings salts from the new mortar with it. This usually fades with rain and weather over the first year or so and doesn't return.
Heavy or long-lasting efflorescence on new work is a different matter. It can mean the brick was stored uncovered and soaked, the wall was left open to rain during construction, or water is getting in through a detail that wasn't built right.
When efflorescence is a warning sign
On an older building, efflorescence that keeps coming back after cleaning means there's a steady supply of water getting into the wall. Where it appears usually points to where the water is coming from.
Deposits just below a parapet or coping stones suggest water getting in from the top of the wall. Under window sills, look at the sills and the sealant around them. Around downspouts and gutters, check for leaks and overflow. At the bottom of the wall near the sidewalk, the likely sources are groundwater rising into the masonry, splash-back from the pavement, soil or planters against the wall, or de-icing salt. On a chimney, suspect the crown, flashing or condensation inside the flue. Our posts on brick wall leaks and chimney repair go into those sources in more detail.
Efflorescence on an interior wall, especially in a basement or on the inside face of an exterior wall, means water is reaching all the way through. That deserves attention even if nothing is dripping.
The damage you can't see: subflorescence
The white powder on the surface is the harmless version. The harmful version happens when salts crystallize just below the surface of the brick instead of on it. That's called subflorescence, or crypto-efflorescence.
As salt crystals grow inside the pores of the brick, they exert pressure. Over repeated wet and dry cycles, that pressure can break off the face of the brick in flakes or powder, a process that looks a lot like freeze-thaw spalling. Soft, older brick is especially vulnerable.
Subflorescence is most likely when something stops water from evaporating at the surface, and the most common culprit is a sealer or coating. That's one reason we tell owners not to seal a wall that's showing efflorescence.
Is it efflorescence or something else?
Not every white deposit on brick is efflorescence, and the difference changes how it gets cleaned.
Efflorescence is soft and powdery or fuzzy. It usually brushes off dry, and it dissolves in water, so it may disappear temporarily after rain.
Lime run or calcium carbonate deposits are hard, crusty white streaks, often running down from mortar joints, cracks or the edge of a slab. They form when water leaches lime out of mortar or concrete and it reacts with carbon dioxide in the air. These don't brush off and don't dissolve in water. A drop of household vinegar will usually fizz on calcium carbonate and not on typical efflorescence, which is a quick way to tell them apart.
Mortar smears or cement film left from sloppy repointing look like a dull gray-white haze across the brick faces, especially near the joints, and appear right after the work rather than months later.
Green, yellow or black staining isn't efflorescence at all. It's usually biological growth or a metallic stain coming from within the brick, and each needs its own treatment.
How to remove it
Start with the gentlest method. Wait for a dry stretch of weather, then brush the deposit off with a stiff, dry nylon brush. Don't use a wire brush. Steel bristles scratch the brick and leave behind metal particles that rust and stain.
Resist the urge to hose it off. Soaking the wall dissolves the salts and carries them right back into the brick, where they'll come out again when it dries, sometimes worse.
Don't pressure wash. High-pressure water erodes mortar joints and the fired face of the brick, and it drives water deep into the wall. On landmarked buildings, LPC limits facade cleaning to water pressure below 500 psi for good reason.
Stubborn deposits, and hard calcium carbonate crusts, may need a masonry cleaner formulated for the type of brick. This is where amateur cleaning does real damage. Strong acids like muriatic acid can etch brick and burn out mortar joints, and on some brick they leave new stains of their own. Any chemical cleaner should be tested on a small, out-of-the-way area first, and the wall should be wetted before it goes on and rinsed thoroughly after.
And keep in mind that cleaning only removes what's already come out. If water is still moving through the wall, the white will return.
How to stop it coming back
The real fix is cutting off the water. That usually means repairing whatever the location of the deposits points to: repointing eroded joints, resetting or resealing coping stones, replacing failed window sealant, fixing sills and flashing, and clearing gutters and downspouts. Our repointing guide covers the most common repair.
At the base of a wall, improve drainage so water runs away from the building instead of toward it, and keep soil, mulch and planters from sitting against the brick. In winter, ask whoever clears the sidewalk not to pile salted snow against the building. Salt that soaks into the bottom courses of brick feeds efflorescence and subflorescence for years.
Don't seal the wall to hide it. As explained above, a sealer can move the salt from the surface into the brick, where it does real damage. A breathable water repellent can be a reasonable last step on a wall that's already been properly repaired, but it isn't a fix for efflorescence.
When to call someone
Brush it off and watch. If it doesn't come back, you're done. If it returns after cleaning, keeps getting heavier, or shows up alongside crumbling mortar, flaking brick or damp patches inside, the wall has an active water problem that's worth diagnosing before it turns into spalling brick and a repair bill. On buildings taller than six stories, those same conditions tend to show up later in a facade inspection report.
Send us a photo
NYC Superior Construction repairs brick facades, parapets and chimneys across New York City, Nassau, Westchester and Rockland counties, and Central and North New Jersey. Send us a photo of the white deposits and the wall around them, and tell us how long they've been there and whether they come back after cleaning. We'll tell you what we think is feeding them. See our masonry restoration page for the repairs we handle.
Frequently asked questions
What is efflorescence on brick?
A white, powdery deposit of salts. Water dissolves salts inside the masonry, carries them to the surface and evaporates, leaving the salts behind.
Is efflorescence harmful?
The surface deposit is mostly cosmetic. It matters when it keeps returning, which means water is moving through the wall, and when salts crystallize under the surface and break off the brick face.
How do I remove it?
Dry-brush it with a stiff nylon brush in dry weather. Avoid wire brushes, soaking and pressure washing. Stubborn deposits may need a professional masonry cleaner tested on a small area first.
Should I seal the brick to stop it?
Generally no. A sealer can trap the salts inside the brick, where they cause spalling. Fix the water source instead.
This article is general information about masonry maintenance, not engineering advice. Test any cleaning method on a small area first, and have persistent moisture problems evaluated by a qualified professional. Last reviewed: September 22, 2026.