Stains on Walls and Ceilings Near the Chimney

First question: what is the stain made of?

Before thinking about where the water or smoke came from, look closely at the stain itself in good light. Most stains near a chimney fall into one of four families.

• Water rings. Tan to brown, often with a darker outline or several nested rings. Each ring usually marks the edge of a wetting that dried. The paint or drywall may be soft, bubbled or sagging in the middle.
• Smoke and soot shadows. Gray to black, soft-edged, with no tide line. They collect above a fireplace opening, along the underside of a mantel, on the ceiling above a stove, or around a connector pipe where it enters the wall.
• Brown bleed-through on the chimney breast. Discoloration on the plaster or drywall that covers the chimney inside the house, sometimes with peeling wallpaper or blistering paint. DuraVent's guide to relining for gas appliances lists wet spots, discolored plaster walls, peeling wallpaper, blistering paint and mildew among the visible results of condensation damage in a chimney.
• White crust or powder. Salt deposits left on a surface as water evaporates from it. The National Park Service's brief on controlling moisture lists efflorescence on interior and exterior surfaces among the common signs of a moisture problem.

It is possible to have more than one at once. A chimney that leaks can also have a flue problem.

When the stain is a reason to stop

Some stains change what you should do today, before anyone works out the cause.

• Soot near any fuel-burning appliance. The Consumer Product Safety Commission lists sooting, rust or water streaking on a vent or chimney, and debris or soot falling from a chimney, fireplace or appliance among signs of a possible carbon monoxide problem. Stop using the fireplace or appliance until it has been checked.
• A carbon monoxide alarm, or symptoms. CPSC names headache, dizziness, weakness, nausea, vomiting, sleepiness and confusion. Get everyone outside to fresh air and call 911.
• A ceiling that sags, drips or feels soft. Wet drywall and plaster can come down. Keep people out from under it, protect the floor, and keep dripping water clear of ceiling lights and outlets.

Map the stain against the chimney

A rough sketch is worth more than a description. The NPS moisture brief recommends using photographs, floor plans and elevations, even roughly sketched, to record every sign of damp or damage. For a stain near a chimney, write down:

1. Distance from the chimneyMeasure from the face of the chimney breast, or from where the chimney would be behind the wall, to the nearest edge of the stain. A stain that touches the chimney is a different case from one three feet away.
2. Which sideNote whether the stain sits on the uphill side of the chimney, the downhill side or one of the flanks, by comparing with the roof slope outside. Uphill-side stains often bring the cricket or back flashing into the conversation.
3. Ceiling or wall, and which floorA top-floor ceiling stain is close to the roof. A stain on a lower floor means water traveled down, inside the masonry, along the chimney or along framing.
4. ShapeA narrow streak running down a wall corner beside the chimney suggests water following the masonry. A round ring out in the ceiling suggests a drip from above at that point.
5. Mark the edgeTrace the outline lightly in pencil with the date, so you can see later whether it has grown.

What the attic can add

If the chimney passes through an attic you can reach, a look there after rain often settles more than anything else. Go only where there is flooring or solid footing; stepping between joists can put a foot through the ceiling below.

• Shine a flashlight on the roof boards and rafters around the chimney. Fresh water shows as dark, damp wood; old leaks leave rings and stains.
• Look at the chimney masonry itself for wet patches, white salt or sandy joints.
• Check insulation around the chimney for wet or matted areas.
• Note any daylight around the chimney where it passes through the roof.

If the attic is dry and the stain is on a lower floor, the water may be traveling inside the chimney rather than around it. That is a useful finding to pass on.

The foil test for a damp chimney breast

A stain on the chimney breast that never seems to dry raises a basic question: is the moisture coming through the masonry, or condensing on the surface from humid room air? The NPS moisture brief describes a simple test that separates the two.

1. Tape a square of foil to the surfacePick the dampest part of the stain and tape the foil down tightly on all four edges.
2. Wait a day or twoLeave it undisturbed while the house runs as usual.
3. Check both sidesMoisture behind the foil means it is coming from the masonry. Moisture on the room side of the foil means it is condensing from the air.

Moisture from the masonry sends attention to the chimney: rain entry, or condensation inside a flue. Moisture from the air points to room humidity and cold surfaces, which is a house question rather than a chimney one. The test is a clue, not a verdict, and it works best on a surface that is damp at the time.

Which season brings it back

Stains that return tell you when the moisture arrives. Our guide to why chimneys leak covers how to keep a storm log. In short:

• After rain or with wind from one direction: rain entry, from flashing, the crown, an open flue or the brick itself.
• After snow and a thaw: meltwater backing up behind the chimney; see ice dams and chimneys.
• Through the heating season, even in dry weeks: condensation in a furnace, boiler or water heater flue; see chimney condensation.
• In humid summer weather on cold surfaces: room-air condensation, which the foil test helps confirm.

Gray shadows above the fireplace

A gray band on the wall above the fireplace opening, or darkening on the underside of the mantel, usually builds up from small amounts of smoke rolling out at the top of the opening. It can come from brief puffs while lighting, or from steady spillage throughout fires. If the band is getting darker each season, smoke is reaching the room often enough to matter. See why smoke comes into the room and why a fireplace won't draw.

Around a stove or insert, soot at a pipe joint or where a connector enters the chimney points to a leak in the venting at that spot. CPSC's checklist advises examining vents and chimneys regularly for improper connections, visible cracks, rust or stains. Candles, oil lamps and other indoor sources can also leave gray marks on ceilings, so note whether the stain is centered on the fireplace or on something else in the room.

Fix the source, then the ceiling

Repainting a ceiling stain before the source is found erases the best evidence you have and usually wastes the paint. A sensible order is: photograph and map the stain; find and repair the source; give the wall or ceiling time to dry out fully; then repair or replace damaged drywall or plaster and use a stain-blocking primer before the finish coat. Soft, sagging or crumbling material generally needs to be cut out and replaced rather than painted.

When we trace a stain back to a chimney, the assessment covers the cap, crown, masonry and flashing from the roof when it is safe, the attic side when it is accessible, a camera run up the flue when it allows, and controlled water testing when the source is still unclear. Every finding is photographed and shared with you before repair work is planned. Related service: chimney leak repair.

Questions homeowners ask

Sources

1. National Park Service, Preservation Brief 39: Holding the Line, Controlling Unwanted Moisture in Historic Buildings (PDF)
2. DuraVent: Relining Chimneys for Gas Appliances (technical guide, PDF)
3. U.S. Consumer Product Safety Commission: Carbon Monoxide, the invisible killer (Publication 464, PDF)
4. U.S. Consumer Product Safety Commission: Carbon Monoxide Information Center

This guide is general information. It can't diagnose a specific chimney; an inspection can.