Chimney and fireplace symptoms
White stains are showing up on the chimney brick
White powder on the brick of a Portland chimney is efflorescence, salt left by water passing through, often rain from a cracked crown or an uncapped flue. It is not a fire hazard; the water behind it is what needs fixing.
Updated
What to do right now
Take a photo of the stain in daylight and note where it sits: near the top of the stack, in a band at the roofline, on the chimney breast indoors, or in the attic. Rub a dry fingertip across it; efflorescence comes off as fine powder, while paint, lime streaks and lichen stay put. Leave the pressure washer alone; blasting water into wet brick adds to the problem.
Likely causes, most common first
Where the water behind the white stains comes from, likeliest first.
- Most common
Rain through a cracked crown or an open flue
The sign: White streaks heaviest in the top few courses, running down from the crown, or a white bloom inside the firebox under the damper.
The fix: The crown is coated or rebuilt and a cap closes the flue, so rain stops entering from the top. Chimney Crown Repair, from $349
- Common
Open or washed-out mortar joints on the weather face
The sign: Powder that follows the joint lines rather than the brick faces, mostly on the sides that take the storms, with mortar you can scratch out with a key.
The fix: The failed joints are raked out and repointed with a mortar matched to the brick, then the face is left to dry. Tuckpointing and Masonry Repair, from $449
- Common
Brick that drinks the rain on an exposed stack
The sign: A general white haze over whole faces after a wet month, on an exterior wall chimney with nothing shading it, and brick that stays dark for days after rain.
The fix: Once the joints are sound and the masonry has dried, a breathable water repellent keeps rain on the surface instead of in the brick. Chimney Waterproofing, from $349
- Common
Moisture condensing inside an oversized or orphaned flue
The sign: White powder on the chimney in the attic or an upstairs chimney breast, nothing leaking in the roof over it, often where a wall-vented furnace left the water heater alone on the flue.
The fix: A camera run shows a wet, scaling flue, and a liner sized to what still vents there stops the condensation. Chimney Inspection, from $129
- Less common
Rain down an uncapped flue soaking the smoke chamber
The sign: White crust on the firebox walls and the smoke shelf, a musty smell, and a flue open to the sky when you look up from the yard.
The fix: A screened cap over the tile, and the smoke shelf cleared of the wet soot that was holding the water. Chimney Cap Installation, from $299
Two minutes of safe checks
Five things anyone can check from the ground or the hearth that locate the water.
- Map where the white sits: top courses mean crown or cap, a band at the roofline means flashing, inside the house means the flue is wet from within or the crown is feeding the stack.
- Rub a dry finger over it: powder that comes off is efflorescence, a chalky film that stays is lime or old paint, and green or gray crust with texture is moss or lichen.
- Watch it through a storm from indoors or the yard: efflorescence fades while the brick is wet and reappears white as it dries, which is the brick breathing water out.
- Open the damper and look up at the firebox walls with a light: a white crust on the back wall or the smoke shelf means water is coming down the flue itself.
- Check the brick an hour after rain stops: a face that stays dark while the rest of the wall has dried is drinking water and will keep blooming.
What the white powder is, and why it is a message rather than a stain
Efflorescence is salt that water dissolved out of the brick and mortar on its way through, carried to the surface and left behind as the water evaporated. Wherever you see it, water went in on one side and came out on the other.
That is the whole meaning, and it is enough. A dry chimney cannot make efflorescence. The powder brushes off and hurts nothing; what hurts the chimney is the water behind it freezing in the brick, softening the mortar and rusting the damper below.
Brush it off dry, not wet. A pressure washer or a hose drives more water into the masonry and brings a fresh bloom as it dries, and harsh masonry cleaners do more damage to old soft brick than the stain ever did.
Efflorescence, moss, lime or paint: telling the white apart
Efflorescence is a dry, loose powder or a thin crystal crust that sits on the surface and wipes off on a finger. If it needs scraping, it is something else.
| What you see | What it is | What it means |
|---|---|---|
| Hard white drips below a joint that do not wipe off | Lime run | Mortar is washing out and setting on the face; the joint above it is open |
| Brush edges and flakes rather than blooms | Old whitewash or paint | An old finish wearing off, not water at work |
| Green, gray or orange growth with texture, on the shaded side | Moss or lichen | It holds water against the brick and later feeds efflorescence, often with white streaks below it |
What fixing the water behind white stains involves
The powder comes off last; the water path is closed first.
Locate the entry
We photograph the stain pattern, look at the crown, cap, joints and flashing from the roof, and run a camera down the flue when the white is inside the house with nothing leaking above it.
Close the path
A cracked crown is coated or re-poured, a cap goes over an open tile, washed-out joints are repointed with a mortar softer than the brick, and bad flashing is replaced.
Let it dry, then protect
Brick that has been wet for a season needs dry weeks before treatment. Then the exterior faces are treated with a repellent that lets the brick breathe; a sealer that traps water would hold it where the next freeze can work on it.
Clean the surface
The efflorescence is brushed off dry at the end, and you get the before-and-after photos with the posted price. A new bloom after a dry month means another path is still open, and the photos show where to look.
White stains on brick: common questions
Are white stains on chimney brick harmful or only ugly?
The powder is harmless, and the water that made it is not. Efflorescence means rain or condensation is passing through the brick, and in a Portland winter that water can freeze inside the masonry on about 32 nights a year, which is what spalls brick and opens joints. Treat the white as an early warning that costs little to act on.
How do I remove efflorescence from chimney brick?
Dry brushing with a stiff nylon brush once the brick has dried, and only after the water source is closed. Washing drives water back in and the bloom returns, and pressure washers and harsh cleaners damage old brick. If it keeps coming back after brushing, the chimney is still wet somewhere, and that is the thing to fix.
Why is there white powder on the chimney in my attic?
Because the chimney is wet from the inside, from the top, or both. An orphaned furnace flue that now vents only a water heater condenses in cold weather and pushes moisture out through the brick in the attic; a cracked crown sends rain down inside the stack to the same place. A camera run tells which.
Will white stains on the chimney come back after a repair?
Not if the water path is closed and the brick has been allowed to dry. Salts already in the masonry may bloom once or twice as the last moisture leaves, which brushes off. A bloom that returns after a dry month means a path is still open, and where the new stain sits points to it.
Does efflorescence on the chimney mean the brick is failing?
Not yet, usually. Efflorescence appears while the brick is still sound; spalled faces, crumbling joints and brick fragments on the ground are what failing looks like, and they follow years of the same water. Catching it at the white-stain stage usually means a crown, cap or repointing job rather than a rebuild.
Related pages
Areas we cover for this
Calls about white stains on brick come in from University Park and Portsmouth, Beaumont-Wilshire, Damascus and Boring and every other part of the metro we serve.
Ready to book a sweep?
Call with what the fireplace is doing, or text a photo of the opening and one of the chimney top, and we will name the service and its posted price before we come out.