Identifying The Types Of Chimney Discoloration

Many homeowners may incorrectly assume that any discoloration on their chimney’s is just a sign of age and use. Unfortunately, any discoloration is usually a sign of a problem with the chimney’s structure. There are many different types of discoloration, ranging in severity, but most will require a certified professional to properly diagnose and treat the issue.


The white staining that is commonly found on older chimneys is called efflorescence. This white crystallized or powdery substance forms when too much moisture is let into the masonry surface. As the excess moisture moves through the masonry walls and evaporates on the other side, it leaves behind salt deposits. The salt deposits are what gives the walls a white appearance. Cracks in the mansory could be causing excess moisture to seep through the chimney walls. While efflorescence is fairly easy to remove and will not cause further damage, it is a sign of a moisture problem in the chimney itself. A certified sweep will be able to remove the white residue from the chimney’s exterior and diagnose what is causing it to form in the first place.

Brown Or Green Stains

These dark stains are often a problem with water damage. This can occur because of excess moisture being allowed to seep through the bricks of the chimney, similar to efflorescence. Or you could have water damage occurring from an outside source. A clogged roof gutter could be causing water to overflow and pour out onto your chimney.This kind of damage will cause the exterior masonry walls to deteriorate quickly, which could cause severe structural issues with your chimney. If moisture is held in the cracks of the chimney, algae may start to grow. If you are seeing stains with a green tint, these are most likely algae or mold. You will need to have a professional seal up these cracks to prevent moisture from collecting, and a water repellant may need to be applied.

Black Stains

Black stains on the outside of a chimney, especially near the top, are usually due to soot wash off. When it rains, the soot left on the chimney cap from evaporating gases washes off and down the exterior of the building. A chimney that is not burning properly could also cause soot to build up on the chimney cap. When a fire is not burning hot enough, the top of the chimney will be much colder than the gases attempting to escape and condensation will occur. This causes particles to stick to the chimney and chimney cap, which is known as soot. You can minimize these unsightly black streaks by having your chimney cleaned and inspected annually. A certified professional will be able to identify any problems with the chimney cap or the performance of the chimney.

Stains on your chimney may seem like just a sign of age, but they are usually a sign of something going wrong with your chimney. A certified chimney sweep will be able to clean the stains and identify why the staining is occurring. If you have staining that hasn’t been checked out, be sure to give us a call today to set up an appointment!


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