Efflorescence is white, powdery salt left on brick when water carries dissolved salts out of the wall and evaporates. To remove it, find and fix the water source first, because the Brick Industry Association says to fix the cause before removal. Then take the powder off gently, starting with the mildest method. Sealing or coating the brick alone is not recommended. If it comes back after the first year, water is likely getting into the wall.
To remove efflorescence from brick, fix the water first and clean second. Efflorescence is salt that water carries out of the wall and leaves as white powder when it dries. Scrub it off without fixing the water and it comes back, usually in a few weeks of damp weather.
This article covers what causes it, how to take it off old Chicago brick without making things worse, and what to repair so it stops. If you only want to know whether it is harming the wall, see is efflorescence bad for brick.
What is efflorescence, exactly?
BIA says efflorescence needs three things at once: soluble salts, water, and a path through the pores of the masonry to the surface. When the water evaporates at the surface, the salts are left behind. The salts usually come from mortar cement alkalis, backing materials, soil or trim, not usually from the brick itself (BIA Technical Note 23A).
What owners notice:
- A white or grayish powder or crust on the face of the brick or on the mortar joints.
- It is worst on walls that stay damp: below parapets and chimneys, under leaking gutters, near the ground and on the north side.
- It comes and goes with the weather, and it is often worst in winter (BIA Technical Note 23A).
Why is it on my brick?
There are two situations, and they are not the same.
New work. BIA calls efflorescence on brickwork less than a year old "new building bloom," and says it usually fades on its own (BIA Technical Note 23A). If you had tuckpointing or masonry done recently, that may be all it is.
An older wall. BIA says efflorescence that appears after the first year usually points to excess water getting into the wall or poor drainage (BIA Technical Note 23A). On a Chicago two-flat or three-flat, the usual suspects are:
- Mortar joints that are open or cracked, letting water in. The City treats masonry joints that are not weather resistant and water tight as an unsafe condition (City of Chicago, 14X-3-303).
- A failing parapet coping, chimney crown or flashing.
- A gutter or downspout that overflows against the wall.
- Soil or planters piled against the brick.
- A hard, cement-based coating or repair that traps moisture. See below.
For leaks, see water coming through a brick wall.
How do you remove efflorescence from brick?
Start with the cause, because BIA says to find and fix the moisture and salt source before removing the salts (BIA Technical Note 23A). Then:
- Let the wall dry out if you can. Some efflorescence dries to powder and brushes off.
- Start with the gentlest method that works. A stiff, natural bristle brush on a small area is where most owners should stop. Do not use a wire brush on old brick.
- Test a small patch first. Pick a spot that does not show and see what the brick does. Old Chicago common brick is soft.
- Stop and call a mason if the powder keeps coming back, if the brick surface is flaking, or if the cleaner you are using starts to change the color of the brick.
- Ask before using any acid or chemical cleaner. BIA points to its Technical Note 20 for removal procedures (BIA Technical Note 23A), and NPS adds that cleaning efflorescence with some methods can liberate additional salts (NPS Preservation Brief 2). Whatever you use, follow the manufacturer's safety directions.
Wear a dust mask when you brush dry powder. If someone dry-grinds mortar to get at the wall behind the powder, that throws silica dust, and OSHA's rule requires tuckpointing grinders with a shroud and dust collection plus respirators (OSHA).
On older brick buildings, the white powder is often a signal, not the problem. We often find it below a leaking gutter, under a chimney that has lost its crown, or on a wall that was patched with hard cement years ago. Owners scrub it every spring and wonder why it returns. The brush was never going to fix the water.
Should you seal the brick to stop it?
Not as the first move. BIA says coatings alone are not recommended to control efflorescence (BIA Technical Note 23A). NPS cautions that water-repellent coatings are appropriate only after a building has been made watertight and dried (NPS Preservation Brief 1). A coating over a wall that is still taking in water can trap the moisture.
That matters on old brick, because trapped moisture and salts can crystallize inside the brick and cause the face to spall or delaminate (NPS Preservation Brief 2). Efflorescence on the surface is usually relatively harmless. The damaging form is salts crystallizing under the surface (NPS and BIA).
How do you stop it coming back?
The fix is on the water side:
- Repair open mortar joints. That means repointing, with mortar softer and more vapor permeable than the brick. See what tuckpointing is and the mortar mistake that ruins Chicago brick.
- Fix gutters, downspouts and drainage so water does not run down or pool against the wall.
- Repair the top of the wall. A bad coping, crown or flashing sends water straight down into the masonry.
- Pick the right season. NPS warns against antifreeze admixtures in repointing mortar because they can add salts that cause later efflorescence (NPS Preservation Brief 2). Ask your mason what is going into the mortar.
- Give it time. New mortar and new masonry carry salts. A little bloom after new work can be normal.
When efflorescence is a warning sign
White powder alone is not an emergency. White powder together with any of these is worth a closer look:
- Brick faces popping off or flaking. See freeze-thaw damage and are spalling bricks dangerous.
- Crumbling or missing mortar.
- Stair-step cracks or a bulging wall. See stair step cracks.
- Powder that comes back in the same place every season.
- Damp or stained interior walls on the same side.
If the water source stays, so does the powder, and whatever else the water is doing in the wall. Chicago requires masonry joints to be kept weather resistant and water tight (City of Chicago, 14X-3-303). Cleaning off the symptom for years while the wall stays wet is how a cosmetic issue becomes a repair.
What to ask before you hire
- Where is the water getting in, and how will you confirm it?
- Will you repair the source before you clean?
- What are you using to clean, and have you tested it on a small patch?
- What mortar will you use if the joints need work?
- Will you coat or seal the brick, and why?
If you want a mason to find where the water is coming from, our masonry crew can look at it. For the rest of the system, see the Chicago brick and masonry guide. For cleaning brick in general, see how to clean Chicago brick.
Common questions
Fix the water source first, then take the powder off with the gentlest method that works, such as a stiff natural bristle brush on a dry wall. Test a small patch first. BIA points to its Technical Note 20 for removal procedures, and NPS notes some cleaning methods can free more salts.
On new work, often yes. BIA says efflorescence on brickwork under a year old, called new building bloom, usually fades. If it shows up after the first year, it usually points to water getting in or poor drainage, and it will keep coming back until that is fixed.
Not on its own. BIA says coatings alone are not recommended to control efflorescence. NPS says water-repellent coatings belong only after the building has been made watertight and dried. A coating over a wall that is still wet can trap moisture.
No. Efflorescence is mineral salt left behind when water evaporates. If what you see is not a dry white powder, or the wall is wet, stained or smells musty, have someone look at the wall in person.
Sources
- Brick Industry Association: Technical Note 23A: Efflorescence, Causes and Mechanisms (PDF)
- National Park Service: Preservation Brief 2: Repointing Mortar Joints in Historic Masonry Buildings (PDF)
- National Park Service: Preservation Brief 1: Cleaning and Water-Repellent Treatments for Historic Masonry (PDF)
- City of Chicago: Code Modernization Ordinance, including Title 14X Minimum Requirements for Existing Buildings (PDF)
- Brick Industry Association: Repointing Brick Masonry (PDF)
- OSHA: 29 CFR 1926.1153: Respirable Crystalline Silica in Construction
Facts last checked: October 7, 2026.
This article explains general rules and common situations in Chicago. It is not legal advice, and City rules change. For a specific property, check with the Chicago Department of Buildings or a licensed professional.