What Are the White Stains on My Chimney?
White, chalky deposits on chimney brick are efflorescence — a sign water is moving through the masonry. What causes it and how to stop it in Northwest Indiana.
NWI Chimney · October 4, 2026
The short answer
White, powdery or crusty stains on chimney brick are efflorescence — salts carried out of the brick and mortar by water, left behind when the water evaporates. The stain itself is harmless, but it tells you water is getting into the masonry. Find and stop the source (crown, cap, flashing or saturated brick) and the white stains stop coming back.
Why it appears
Brick, mortar and concrete contain natural salts. When water soaks through and then dries at the surface, it carries those salts with it and leaves them as a white bloom. It's common in spring, after a winter of snow against the chimney, and on the side that takes the most wind-driven rain.
What it can point to
- A cracked crown letting water into the top of the chimney
- No cap, so rain soaks the flue and the brick around it
- Flashing gaps where the chimney meets the roof
- Inside the house: water coming down a gas or furnace flue, or condensation in an unlined flue
What to do
Brush it off dry with a stiff brush. Don't pressure-wash — it pushes more water into the brick. If it keeps coming back, have the top of the chimney checked. Our Level 1 inspection is free and photographed.
What the fix costs
It depends on the source: crown sealing $250–$450, a stainless cap $250–$400, flashing repair $300–$600, and a breathable masonry water repellent $300–$900 once the masonry is sound.
More answers
Is efflorescence the same as mold?
No. Efflorescence is mineral salt; it's white and crumbles to powder. Mold is usually fuzzy, green or black, and grows on organic material.
Will waterproofing stop efflorescence?
A breathable repellent helps once the leak sources are fixed. Sealing over a leak traps water and can cause spalling.
Why are there white stains inside on my basement chimney?
Often water or condensation coming down the flue, especially from a gas furnace or water heater in an unlined or oversized chimney.
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