Stains indicate chimney leaks and damage (C) Daniel Friedman

Chimney Stains, Discoloration, Leak, Diagnosis, Cleaning & Repair Guide
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Detailed Inspection & Photo Guide to stains on masonry and metal chimneys
What do dark oozing stains mean on a metal or masonry chimney exterior indoors or outside?
What do white powdery stains mean when found on a masonry chimney exterior indoors or outside?
Diagnosis of brown or black stains on chimney walls
Questions & answers about the cause, significance, and cure of stains on chimneys both outside and within buildings

This article describes stains that appear on chimney surfaces both indoors and outside. We identify common dark brown or black stains as well as white or light-colored stains or white powdery material that appears on masonry chimney surfaces. We explain what these chimney stains might mean, why safety hazards may be present, and how to proceed to inspect and repair the chimney.

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Significance of Stains on a Chimney Exterior Surface: Creosote, soot, water

Here we discuss stains found on or at chimneys themselves both on the building exterior, and in the building interior at walls or ceilings near chimneys. Also see Chimney-Caused Roof Stains where we discuss staining on roof surfaces traced to problems at chimneys.

Water and Chimney Leaks Lead to Damage

Brown or black oozing stains may appear on both masonry chimney and metal chimney exteriors, though if the metal chimney was properly assembled such leaks onto the metal chimney exterior surface are unlikely.

The brick chimney at left has both white and black stains as well as what looks like a vertical crack along its right side - this chimney maybe unsafe and needs prompt investigation.

The brick chimney with brown-black stains oozing from between the next chimney's mortar joints (photo at below left) tells us that water has been entering the chimney flue (missing rain cap or improper chimney top cap/crown seal or other chimney leaks).

These brown chimney stains may be still more significant: they may indicate that the chimney flue is unlined and possibly unsound and unsafe.

The pair of photos above teach several additional important chimney inspection lessons:

It is important to notice stains on a chimney exterior surface: stains from water, creosote, or soot leaking out of a chimney such as in this attic. The stains tell us that water has been entering the flue, raising an alert for frost damage. This is not just a cosmetic concern: flue gases and sparks can enter the building.
Water leaking into a chimney increases the chance of damage to the chimney flue or chimney structure.
Inspection distractions: Don't let one observation at a chimney distract you or convince you that further up-close inspection is not needed. When we crowded in around the corner to see the side of this chimney we found the gaping hole in the photo at right.
Looking into a chimney through any opening that presents itself an tell us immediately whether or not the flue is lined and what is the thickness (and thus some information about safety) of the chimney walls. Finding a chimney liner does not assure that the whole flue is lined and in good condition, but finding no chimney flue liner and a single wythe brick construction in any location tells us something important about the chimney safety.

These black stains on a masonry or metal chimney are not mold. (Mold prefers to grow on organic materials.)

Significance of White Efflorescence Stains on Chimneys -

Effloresence white stains on a chimney (C) Daniel Friedman

White powdery or crystalline stains on masonry chimneys is often efflorescence, a mineral salt left on the surface as water evaporates.

Efflorescence may appear on the outside surfaces of a chimney both outdoors and inside as well as inside the flue itself.

(You are not likely to see these stains on a metal chimney unless the metal chimney and flue are damaged and leaking insulation material.)

Efflorescence might be just cosmetic - as wind-blown rain wets the chimney sides and leaches out mineral salts which remain white on the masonry surface of the chimney.

But efflorescence might also mean that water is running inside of the chimney flue or chimney structure. Further diagnostic inspection is needed.

Left unattended, water entering a masonry chimney risks damage to the flue (unsafe) and to the chimney structure (unsound and unsafe).

Other examples of efflorescence on building foundation walls is in our discussion of white stuff that is not mold.

At SLATE ROOF DEFECTS Questions & Answers we provide additional discussion about sources of white stains that may be found on chimneys or on roofs below or near chimneys.

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Attic Chimney Inspection
  Holes in Masonry Chimneys
  Dark Stains on Chimney Surface
  White/Light Stains on Chimneys

Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
NFPA 211 - Standards for Chimneys & Fireplaces, NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 Edition (older editions and standards are found at the same bookstore)
NFPA #211-3.1 1988 - Specific to chimneys, fireplaces, vents and solid fuel burning appliances.
NFPA # 54-7.1 1992 - Specific to venting of equipment with fan-assisted combustion systems.
GAMA - Gas Appliance Manufacturers' Association has prepared venting tables for Category I draft hood equipped central furnaces as well as fan-assisted combustion system central furnaces.
National Fuel Gas Code, an American National Standard, 4th ed. 1988 (newer edition is available) Secretariats, American Gas Association (AGA), 1515 Wilson Blvd., Arlington VA22209, and National Fire Protection Association (NFPA), Batterymarch Park, Quincy MA 02269. ANSI Z223.1-1988 - NFPA 54-1988. WARNING: be sure to check clearances and other safety guidelines in the latest edition of these standards.
Fire Inspector Guidebook, A Correlation of Fire Safety Requirements Contained in the 1987 BOCA National Codes, (newer edition available), Building Officials and Code Administrators International, Inc. (BOCA), Country Club HIlls, IL 60478 312-799-2300 4th ed. Note: this document is reissued every four years. Be sure to obtain the latest edition.
Uniform Mechanical Code - UMC 1991, Sec 913 (a.) Masonry Chimneys, refers to Chapters 23, 29, and 37 of the Building Code.
New York 1984 Uniform Fire Prevention and Building Code, Article 10, Heating, Ventilating, and Air Conditioning Requirements
New York 1979 Uniform Fire Prevention & Building Code, The "requirement" for 8" of solid masonry OR for use of a flue liner was listed in the One and Two Family Dwelling Code for New York, in 1979, in Chapter 9, Chimneys and Fireplaces, New York 1979 Building and Fire Prevention Code:
"Top Ten Chimney (and related) Problems Encountered by One Chimney Sweep," Hudson Valley ASHI education seminar, 3 January 2000, contributed by Bob Hansen, ASHI
Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
"Rooftop View Turns to Darkness," Martine Costello, Josh Kovner, New Haven Register, 12 May 1992 p. 11: Catherine Murphy was sunning on a building roof when a chimney collapsed; she fell into and was trapped inside the chimney until rescued by emergency workers.
"Chimneys and Vents," Mark J. Reinmiller, P.E., ASHI Technical Journal, Vol. 1 No. 2 July 1991 p. 34-38.
"Chimney Inspection Procedures & Codes," Donald V. Cohen was to be published in the first volume of the 1994 ASHI Technical Journal by D. Friedman, then editor/publisher of that publication. The production of the ASHI Technical Journal and future editions was cancelled by ASHI President Patrick Porzio. Some of the content of Mr. Cohen's original submission has been included in this more complete chimney inspection article: InspectAPedia.com/chimneys/Chimney_Inspection.htm. Copies of earlier editions of the ASHI Technical Journal are available from ASHI, the American Society of Home Inspectors.
Natural Gas Weekly Update: http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp Official Energy Statistics from the U.S. Government
US Energy Administration: Electrical Energy Costs http://www.eia.doe.gov/fuelelectric.html

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
Chimney & Stack Inspection Guidelines, American Society of Civil Engineers, 2003
NFPA 211 - 3-2 - Construction of Masonry Chimneys
NFPA 211 - 3-3 - Termination Height for chimneys
NFPA 211 - 3-4 - Clearance from Combustible Material
NFPA 54 - 7-1 - Venting of Equipment into chimneys
Brick Institute of America - Flashing Chimneys
Brick Institute of America - Proper Chimney Crowns
Brick Institute of America - Moisture Resistance of Brick
American Gas Association - New Vent Sizing Tables
Chimney Safety Institute of America - Chimney Fires: Causes, Effects, Evaluation
National Chimney Sweep Guild - Yellow Pages of Suppliers
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Significance of Stains on a Chimney Exterior Surface: Creosote, soot, water

Water and Chimney Leaks Lead to Damage

Significance of White Efflorescence Stains on Chimneys -

Questions & Answers regarding this article

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Technical Reviewers & References

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