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Tips to Identify the Cause of Staining on Chimneys

white chimney staining on chimneyDiscoloration of a chimney can occur for various reasons, and the staining gives evidence of significant chimney damage in nearly every instance. Oftentimes, homeowners think discoloration is a natural part of aging of the chimney structure, but that’s rarely the case. In order to curb further deterioration, it’s best to hire a licensed, certified chimney professional, who can identify the cause of the chimney staining and properly address the issue.

Black Stains

Sometimes black stains are a sign of age combined with frequent use, but more frequently they are evidence of some type of problem. The soot that washes down the chimney exterior could be from evaporating gases. Usually when soot buildup is on a chimney cap, it indicates improper burning. If a fire is not hot enough the gases moving up the chimney could be warmer than the top of the chimney, which is still cold. This results in particles or soot sticking to the chimney cap and top of the chimney lining. When it rains, the soot then causes unsightly black streaks.


“Efflorescence” is a word that means “to flower out” in French. On your chimney, efflorescence means that salt deposits inside the masonry have evaporated on the surface of the masonry exterior with the appearance of flowering crystals. The staining is usually white but could also be yellow or brown in tint. The color depends on the type of mineral the salt is emanating from. Efflorescence can be removed fairly easily, such as with pressured water or a strong brush. That doesn’t usually solve the problem, however.

Efflorescence usually means that water has infiltrated the masonry system. When there is moisture inside, the water expands and contracts in freezing and thawing weather cycles. Ultimately, if the problem isn’t addressed, the masonry will begin to break and flake off, which can lead to a leaning or collapsed chimney. This type of damaging water intrusion often exists without efflorescence. The following conditions must exist for efflorescence to occur:

  • Water-soluble salts must be present in the masonry.
  • Moisture enters the masonry so that the salts are transformed into a soluble solution.
  • The salts must be able to move through the masonry to the exterior surface.

Green or Brown Stains

Chimneys are built in a way that protects the chimney walls from constantly having water flowing over the masonry. Various things can go wrong on the roof that causes the chimney to be exposed to excess water, resulting in accelerated deterioration. Algae or mold can begin growing in the chimney cracks, resulting in green or brown stains. Application of water repellant can help to prevent this type of problem. Also, a structure called a “cricket” can be constructed to divert excess water away from the chimney stack.

White and Brown Staining

Staining associated with chimney damage doesn’t always appear on masonry. A home with siding on the outside of a chimney can become stained, as well. Brown and white staining is usually an indication of moisture coming through the chimney masonry. Sometimes excess moisture is caused by migration of condensation of moisture from exhaust gases from the furnace. It often requires the expertise of a chimney specialist to determine the cause of staining.

fishkill ny professional chimney repairWho to Call if you have Chimney Staining

Experts like the licensed, certified chimney sweeps at Hudson Valley Chimney can identify the cause of chimney stains and provide needed repairs. Regular maintenance and annual chimney inspections can cut repair costs, since extensive chimney damage can be prevented. Call Hudson Valley Chimney today at 800-439-1071 if you have chimney staining and for all of your other chimney needs.

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