Identifying Chimney Discoloration

Nothing can mar a beautiful chimney more than unsightly staining or discoloration. In addition to being an eyesore, chimney discoloration can often be the sign of a more serious chimney or fireplace problem. The following are some of the most common chimney stain colors and their causes.

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Black stains

While most soot stains are the result of age or lack of regular cleaning and maintenance, soot staining can also indicate a hidden chimney problem. Interior soot stains are more common in older homes with open hearth fireplaces. While this kind of soot staining may be an eyesore, it is usually indicates that a fireplace has not been correctly cleaned or the wrong kind of firewood was being burned.

On the exterior of the chimney, black and dark brown stains are often caused by excess creosote. Creosote buildup can be caused by burning unseasoned or green wood, allowing fires to smolder at low temperatures, a flue that is improperly sized for the firebox, or not having the chimney regularly swept. Creosote buildup should be addressed as soon as possible as it is a highly flammable substance that is the leading cause of chimney fire.

When the creosote buildup is bad enough to cause exterior staining, the chimney may need to be relined. Gas burning fireplaces and inserts should never have exterior soot stains; exterior soot staining on a gas fireplace can indicate a carbon monoxide leak or other equally dangerous malfunctions.

Dark green stains

Dark green stains or discoloration on the outside of a chimney is caused by algae growth. This kind of discoloration is often seen in areas where water has been allowed to pool or consistently flows, such as on a chimney where the chimney crown does not have an appropriate overhang. Because it is so difficult to differentiate between dark green algae stains and brown or black stains caused by soot, a chimney inspection may be needed in order to determine the cause of the discoloration.

Red stains

Red or red-brown stains are most often seen on the sides of metal or prefabricated chimneys. This kind of discoloration is caused by the metal of the chimney chase cover rusting. When rust stains begin to appear on the side of the chimney chase, it is a sign that the chase cover may be leaking or letting water into the chimney and fireplace. Rusted chimney chase covers should be replaced as soon as possible to prevent water damage to the fireplace and chimney.

White stains

Powdery or crystalline white discoloration on chimneys is known as efflorescence. Efflorescence is the white mineral salt left behind as water evaporates. Rain, ground water, and even sprinklers can all cause efflorescence to appear on a chimney’s exterior; however, interior efflorescence stains almost always indicate the presence of a chimney leak.

You don’t have to live with discoloration on the sides of your chimney. Contact Mason’s Chimney Service today for more information on removing unsightly chimney discoloration – and how to keep it from coming back.