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Wednesday, July 18, 2012

Spalling brick a sign of severe moisture damage

When chimneys spall, it is a sign of severe moisture penetration of the masonry bricks or stone. Spalling is the flaking off of a brick or stone surface, and is evident when the face of the masonry is missing. Pieces of bricks or stones may be found on the ground or on the roof, which is an indication that there is a problem. This is a common issue in the Kansas City and Midwest area.

Spalling is caused when the masonry absorbs too much moisture from rain and is subjected to freeze/thaw cycles. Damages can be exacerbated by condensation of flue gasses in improperly sized flue liners and gaps or cracks in mortar joints on the interior of the chimney, and by moisture entering the interior of the chimney chase from the top at the cement crown area where cracks or gaps allow water to enter.   If the cement crown is not built with a poured crown with 2” overhand and drip edge per code, damages to the top of the chimney structure will occur more quickly. However, builders seldom build poured crowns due to the added time and expense involved.

Soft type brick is more susceptible to moisture penetration than hard type bricks, but builders often use soft brick because they are less expensive. When building a new home, homeowners should request that hard bricks be used in all construction so they will last many years.

Chimneys usually show damages more extensively because they are more exposed to the elements than the rest of the house. The top portion of the chimney will show the first signs of moisture problems. By the time bricks or stones spall, the damage is done. Spalled bricks or stones cannot be repaired and must be replaced. It may be tempting to save money by replacing spalled bricks and doing partial rebuilding of a chimney, but keep in mind that the entire chimney will need to be rebuilt at some point, so any partial repair is a temporary fix.

Painting chimneys is never a good idea. This servies to temporarily cover up the problem, but will speed up the deterioration process since the bricks can't breathe.  Buyer beware if you see a painted chimney.

The application of masonry water repellant sealer can help stop further penetration of moisture, but bricks that already have interior damage will continue to spall. Masonry water repellant should be applied every year to every five years, depending on when it loses its ability to shed water off the bricks. Professional chimney contractors prefer to use Chimney Saver brand water repellant.

To find a qualified chimney restoration contractor in the greater Kansas City area visit the Midwest Chimney Safety Council or the Masonry Heater Association of North America website.


  1. One of the best solutions to prevent bricks from spalling is to coat the bricks with a sealant. This will prevent moisture build-up, which causes bricks to spall. Be mindful that too much application is never a good idea; bricks do need to breathe. This technique is ideal since it is easy to do and inexpensive.

    Linda Wise

  2. Sometimes, spalling chimney bricks are hard to salvage, especially when the fracture has already widened and the bricks are already disintegrating. Prevention is surely effective, but when it’s too late to do anything, it’s best to replace the damaged chimney bricks. When planning to rebuild the chimney or some bricks, make sure you create a design that minimizes water intrusion; that’s another effective way to prevent such conditions.

    Sierra Nordgren

  3. Traditional chimneys, or often called masonry chimneys, are very durable but the bricks are commonly subjected to regular exposure to heavy rain storms and other elements. An excellent preventive measure that can be practiced is to seal the bricks from water by applying quality water repellent made from a silane compound. Annual cleaning and inspection are also equally effective.

    Cody Charlebois


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