Every crew has taken this call. The owner scrubbed the white powder off the brick in the spring, and by fall it's back in the same spots. Now they want a stronger cleaner. What they actually need is a walk around the building in the rain, because that powder isn't dirt sitting on the wall. It's coming out of the wall. Efflorescence is the brick telling you where the water is, and until you deal with the water, no amount of scrubbing keeps it gone.
What efflorescence actually is
Efflorescence is salt. Brick, mortar, the soil against the foundation, and even the water itself can carry soluble salts, mostly sulfates and carbonates. Water soaking into a wall dissolves those salts and carries them along. When it reaches the face and evaporates, the salt stays behind, crystallizing as that white, fuzzy or chalky film.
It takes three things at once: salts in or behind the wall, water to dissolve them, and a path for that water to reach the face and evaporate. Take any one away and efflorescence stops. You can't get every bit of salt out of a wall, and the face is always where it dries. Water is the one you can control.
Why it keeps coming back
Brushing removes what has already reached the surface. It does nothing about the salt still in the wall or the water feeding it. As long as water keeps moving through the masonry, it keeps dropping salt at the face, so the bloom comes back in the same places after the next wet spell.
Those places are your best clue. Efflorescence collects where the wall stays wettest: beside a leaking or disconnected downspout, under a gutter that overflows, below window sills that shed water down the face, under a cracked chimney cap or open parapet coping, and along the base where splash-back, sprinklers, or poor grading keep the bottom courses soaked. Read the pattern and it will usually walk you to the source.
How to tell it from something worse
Plain efflorescence sits on top of the brick. It's soft, powdery or fluffy, and usually brushes off dry, leaving a sound face underneath. On its own it's cosmetic, but it's a moisture warning.
The one to worry about is subflorescence, sometimes called cryptoflorescence. Same salts, same water, but the crystals form just under the surface instead of on it. That tends to happen when something slows drying at the face, like a film-forming sealer, or a wall too wet to dry out between storms. Crystals growing inside the pores push outward, and the face flakes, powders, or pops off. White deposits along with spalled faces, sanding brick, or flakes piling up at the base mean you're past cosmetic.
Timing tells you something too. New brickwork often blooms in its first months as construction moisture works out of the brick and fresh mortar. That new-building bloom usually fades within the first year or so as the wall dries and weather washes it off. Efflorescence that keeps returning to the same spots year after year is chronic, and chronic means an ongoing water source.
One look-alike: a hard white crust or streaks running from the joints that won't brush off. That's usually calcium carbonate hardened on the face, and it needs a different approach (step 4 below).
How to fix it, in the right order
Order matters here more than product.
- Find and stop the water. Clean and repair gutters, reconnect and extend downspouts so they discharge away from the wall, repoint open joints, repair failed flashing, and fix caps, copings, and sills so water sheds off instead of soaking in. Check the grade and aim sprinklers away from the brick.
- Let the wall dry. Often weeks or a full season, depending on how saturated it was. Expect some more bloom while it dries; that's salt still working out, not a failed repair.
- Dry-brush light deposits. A stiff natural-fiber masonry brush on a dry day takes most efflorescence off. Sweep up what falls so the salt doesn't wash back into the soil against the wall.
- Treat stubborn deposits carefully. For hard carbonate crusts or mineral scale on fired clay brick and other acid-tolerant masonry, a professional masonry cleaner is the next step, but only after a test patch in an inconspicuous spot passes. Pre-wet the wall with clean water, dilute exactly as the product data sheet says, allow only the stated dwell time, and don't let the cleaner dry on the wall. Then rinse thoroughly from the top down. Wear eye or face protection and chemical-resistant gloves, protect glass, metal, painted finishes, plants, and soil, and dispose of the rinse residue as the safety data sheet directs.
- Only then consider a repellent. Once the leak is fixed and the wall has dried, a breathable, penetrating silane-siloxane water repellent on above-grade brick can cut down how much rain the brick absorbs while still letting water vapor out. It's the last step, not the first.
What not to do
- Don't pressure wash. High pressure drives water deep into the wall, dissolves more salt to come out later, and can erode brick faces and soft joints.
- Don't seal a wet wall. Putting a coating or repellent on a wall that's still wet and full of salt can push the drying point behind the treated layer, and that's how surface efflorescence turns into subflorescence and spalling. Film-forming sealers are the worst offenders.
- Don't put acid on limestone, marble, or other calcareous stone. Acid cleaners attack calcium carbonate, which is what those stones are made of. Use the same caution on historic lime mortar unless a test on that exact wall passes.
- Don't scrub it off with a bucket of water. Wet scrubbing redissolves the salt and sends it back into the brick to resurface. Brush it dry.
When to call a mason
Bring in an experienced mason if the efflorescence keeps coming back after the obvious water sources are fixed, if you're seeing spalling, flaking, or powdering brick, or if dampness and staining show up inside. Hidden flashing failures, widespread failed joints, and moisture wicking up from the ground need someone who can open the wall and find the real cause. On historic buildings, talk to a preservation mason before using any chemical cleaner, and check with the local historic commission if the property is listed.
For the brushing, our Masonry Brush - Natural Tampico Fiber has 4" acid- and alkali-resistant tampico bristles. When a deposit won't brush off and the brick is acid-tolerant, Pro Mason Masonry Restoration Cleaner is made for carbonate efflorescence and mineral scale on compatible brick and masonry. It's for trained crews, after a passing test patch, never on limestone, marble, travertine, or other calcareous stone, and on historic lime mortar only if a mock-up on that exact wall passes. Once the leak is fixed and the wall is dry, Masonry Responder is a breathable, non-film-forming silane-siloxane repellent for above-grade masonry that sharply reduces water absorption while letting vapor pass.
For more on keeping water out of the wall, read How to Protect Brick and Mortar Joints from Water Damage and Understanding Sealers vs. Water Repellents for Masonry Preservation. If the white deposits come with crumbling brick and hard gray joints, see When the Joints Look Perfect but the Brick Is Crumbling.
