Chimney Stains & Solutions

April 6, 2009 By

Have you looked at your masonry chimney lately?

If so you have probably noticed some discoloration throughout the chimney brick or stone, particularly in the upper portion of the structure.  This is a sure sign of excessive water infiltration into the chimney shell and if not taken care of can lead to costly damage with premature deterioration.

Excessive water in a chimney shell can manifest in three ways: efflorescence, mold growth and spalling.  One or two of these symptoms could be visible on your chimney or all three depending on the severity of the problem.  Let’s take a look at each of these symptoms and the recommended solutions, so that you can protect your chimney from un-wanted damage.

Efflorescence – Efflorescence is a white power that is visible on the surface of the brick or stone (masonry) of your chimney shell.  Water that is inside of a chimney will dissolve soluble salts in the brick and mortars.  As the water migrates to the outside surface of the chimney by wicking action it carries these soluble salts with it and then deposits them on the surface of the masonry during evaporation.

Solution: As with any water problem you must stop the water from entering at the source.  Most water entering a chimney comes in through the top of the chimney or the chimney crown.  Cracks allow water in during each rain so all cracks must be filled and sealed to prevent them from leaking.  The crown should be inspected annually and necessary repairs done to keep it from leaking. You may remove the efflorescence with a stiff brush while applying a neutralizer made of 1 cup of household bleach mixed with five gallons of cold water.  Several applications may be necessary.
Mold – Mold can be but not usually, seen directly.  It manifest by a slight darkening the masonry on the chimney shell.  Since most of the water entering a chimney comes in through the top, most of the mold will be present there and you will notice a definite difference in the masonry tonal color range from the top of the chimney to the bottom.

Solution: An application of a heavy degreaser or detergent as purchased from a pressure washing supply company will usually do the trick in removal of most surface molds.  Soak the chimney with a hose before applying the detergent then let set for approx. fifteen minutes.  Then use a pressure washer to remove the detergent and the mold.

Spalling – Spalling is the action of the de-lamination of the face of brick or stone masonry unit.  It is caused by excessive water within the pores of the unit freezing and thawing over hundreds of cycles. The constant freezing action breaks the pores of the brick apart and causes the face to fall off.

Solution: If only a few bricks are spalled you may get by with re-surfacing the brick face or removal and replacement.  If the damage is wide spread, particularly in the upper portion of the chimney then removal of the damaged portion of the chimney will be required.  Again the chimney crown must be waterproof in order to prevent this damage from occurring.  Remember though, once a brick has spalled it has basically lived its’ useful life and will begin to act like a sponge by absorbing more water so replacement and rebuilding is the preferred long term repair method. 

All three of these problems can be prevented by the installation of a quality chimney crown.  Talk to your masonry professional for additional information.

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