White Powder on Brick or Stucco? What It Means

Short answer

White powder on masonry or stucco is efflorescence: salts dissolved by water inside the wall and left behind on the surface when that water evaporates. The powder itself is mostly cosmetic and brushes off dry. It is a sign that water is moving through the material. A light bloom after a wet spell or on new masonry often fades on its own. If it keeps coming back in the same place, there is an ongoing water source (a failed sealant joint, a missing cap or flashing, splashback, or moisture wicking up from the ground), and that is what needs fixing. Do not pressure-wash it, and do not seal over it with a coating that stops the wall breathing.

Brick repair at the base of a wall, new mortar pointed into damaged joints, on a FAIME commercial job in Vaughan — Brick repair at the base of a wall on a FAIME commercial envelope job in Vaughan. The base of a wall is where water and salts collect first.

What the white powder actually is

Brick, mortar, concrete, stucco and parging all contain water-soluble salts. When water gets into the material, it dissolves those salts and carries them toward the surface. When the water reaches the face and evaporates, the salts stay behind as a white, crystalline, often fluffy deposit. That deposit is efflorescence.

So efflorescence always needs three things at once: salts in or behind the material, water to dissolve them, and a path for that water to travel out and evaporate. Take away the water and the bloom stops. That is why the useful question is never "how do I get rid of the powder" but "why is this part of the wall wet".

Usually harmless

A light, even bloom on new brickwork or fresh stucco, sometimes called new-building bloom, which tends to fade as the wall dries out
A one-off bloom after a very wet spell that brushes off and does not come back
Powder that dissolves in water and brushes away dry

Worth investigating

The same patch returning season after season, which means a water source that has not gone away
Efflorescence concentrated below a window, a sill, a cap or a joint, pointing straight at the detail letting water in
Heavy deposits at the base of a wall or on a foundation, suggesting splashback or ground moisture wicking up
Flaking, crumbling or spalling brick face where the bloom forms
A hard white crust that does not brush off (see below)

A two-minute test to tell what you have

Not every white mark on a wall is efflorescence, and the difference changes what you do about it.

Brush, then wet

Try a dry, stiff brush on the deposit first. Efflorescence is soft and powdery and mostly brushes away. Then put a few drops of water on what is left: efflorescence salts dissolve. A deposit that is hard, crusty and runs in streaks from a joint or crack, and does not brush off or dissolve, is more likely lime run (calcium carbonate), which forms when water leaches lime out of mortar or concrete and it hardens on the face. Lime run points to the same kind of water problem, but it is much harder to clean off and usually needs a professional. Fuzzy, grey-green or black growth is not efflorescence at all. It is organic growth and has a different fix.

Where it shows up tells you where the water is

Efflorescence is a map of where water is moving through your wall. Reading where it forms is usually the fastest way to find the leak behind it.

Under windows and sills. Failed or missing caulking at the window perimeter, a sill with no slope or drip, or a sill joint that has opened up. Water runs in at the sill and comes out as a bloom below it.
Below the top of a wall, a parapet or a ledge. A missing or failed cap, coping or flashing letting rain straight into the top of the masonry.
Around downspouts and gutters. An overflowing gutter or a downspout discharging against the wall keeps one section soaked.
At the base of the wall and on foundations. Splashback from hard paving, soil or mulch piled against the wall, or ground moisture wicking up through the foundation and parging.
Along a vertical line or joint. A control joint whose sealant has failed.
Inside a basement. On a foundation wall indoors it means water is moving through the foundation from outside. That is a waterproofing and drainage question, not a finishing one.

How to clean it without making it worse

Cleaning off efflorescence is easy. Cleaning it off in a way that does not push more water into the wall takes a bit of restraint.

Wait for a dry spell and dry-brush it. A stiff natural or nylon brush removes most efflorescence. Avoid wire brushes on soft brick or stucco finishes, which scratch the face.
If you need water, use as little as possible. A light rinse after brushing, then let the wall dry fully. Soaking the wall re-dissolves salts deeper in the material and brings a fresh bloom back out.
Do not pressure-wash it. High pressure drives water deep into masonry and joints, which feeds the next round of efflorescence and can damage mortar and softer brick.
Be careful with acid cleaners. Diluted acid products can remove stubborn deposits and lime run, but they can etch brick, burn mortar joints and discolour the wall. They are a product-specific, test-patch-first job, not a first resort.

What not to do: sealing over it

The most common mistake is to clean the bloom off and then coat the wall with a sealer or paint that does not let moisture out, on the theory that the wall will then stay clean. It usually makes things worse.

If water is still getting into the wall and can no longer evaporate from the face, the salts crystallise just behind the surface instead of on it. Crystals growing under the face push it off: brick spalls, parging lets go in sheets, and paint or coating lifts off the wall. That damage is permanent, where the efflorescence was not. Masonry and cementitious finishes need to stay vapour-permeable. Any coating that goes on them has to be chosen for that, and only once the water source is fixed.

Fixing the cause, not the powder

A lasting fix is always about the water. Depending on what the pattern points to, that means:

Find the source from the pattern

Walk the wall after rain and note where the bloom forms relative to windows, sills, caps, joints, downspouts and grade. The pattern is usually specific enough to point at one detail.

Redo failed sealant and caulking

Cut out failed window perimeter caulking and control-joint sealant back to clean surfaces and run new joints properly. Do not caulk over the old bead.

Repair the masonry and stucco

Repoint open or eroded mortar joints, replace spalled units, and repair cracked stucco and parging so water is not getting straight in through the face.

Deal with water at the top and bottom

Caps, copings and flashings at the top of the wall, and splashback, grading and downspout discharge at the base.

Let it dry, then clean and finish

Give the wall time to dry out, dry-brush the remaining salts, and only then apply any breathable finish or coating.

Where FAIME fits

Stucco and brick repair, parging, joint sealants and window caulking, and exterior painting are all self-performed FAIME scopes across Toronto, North York, Scarborough, Vaughan, Richmond Hill, Markham, Mississauga, Brampton and the wider GTA. Efflorescence is usually a sign that one of those details has failed.

On our Vaughan commercial envelope project, the order of work was exactly the one above: brick and stucco repairs, old penetrations removed and patched, every joint sealant and window caulking line cut out and redone, and only then the finish coats and paint. Our foundation refinishing project shows the same logic at the base of a house.

We do not diagnose from photographs, because the pattern is only half the story. The other half is what the wall sounds and feels like, and what the details above it are doing. The site visit is free, and we will tell you if a bloom is cosmetic and will fade on its own.

$2M general liability · Active WSIB (Class G5) · 2-year workmanship warranty
Written scope before work starts, naming the water source we are fixing

Frequently Asked Questions

Is efflorescence harmful to my house?

The white powder itself is mostly harmless and brushes off. What it signals can matter: water moving through the wall. A light bloom on new masonry or after a very wet spell often fades on its own. Efflorescence that keeps returning in the same place means a continuing water source, and prolonged wetting plus freeze–thaw can damage brick, mortar, stucco and parging over time.

Will efflorescence go away by itself?

On new brickwork or fresh stucco it often does, as the material dries out and the available salts are used up. On an older wall it will keep coming back for as long as water keeps getting in. Cleaning it off without fixing the water source only buys a few months.

Can I pressure-wash efflorescence off?

It is not recommended. Pressure washing drives water deep into the masonry and joints, which dissolves more salts and brings a fresh bloom back out, and high pressure can damage mortar and softer brick. Dry-brush it in dry weather and use as little water as possible.

Should I seal the brick to stop efflorescence?

Not as a fix on its own. If water is still getting into the wall, a coating that stops it evaporating from the face makes the salts crystallise behind the surface instead, which can spall brick and push off parging and paint. Fix the water source first. Any coating afterwards has to be breathable.

What is the difference between efflorescence and lime run?

Efflorescence is soft and powdery, brushes off and dissolves in water. Lime run is a hard, crusty white deposit, often in streaks from a joint or crack, formed when water leaches lime out of mortar or concrete and it hardens on the surface. Both point to water moving through the wall, but lime run is much harder to remove.

Does FAIME fix the cause of efflorescence in the GTA?

Yes. Brick and stucco repair, parging, joint sealants, window caulking and exterior painting are self-performed FAIME scopes across Toronto, Vaughan, Richmond Hill, Markham, Mississauga, Brampton and the wider GTA. FAIME is WSIB Active under Class G5, carries $2M general liability and backs its workmanship with a 2-year warranty. Site visits are free and no pricing is given before the wall has been seen.

White Powder on Your Brick or Stucco? What It Is Telling You