Moisture Damage in a Chimney Foundation

Moisure has the potential to damage all areas of your chimney.

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According to the Chimney Safety Institute of America, water and moisture damage affects chimneys more than a fire does. The chimney on your roof faces constant danger from the elements, including snow and rain. The chimney foundation is particularly susceptible to moisture damage as the air temperature changes and the materials slowly expand and contract.

Related Searches: Freeze/Thaw Cycle

The freeze/thaw cycle occur as temperatures fluctuate. Cold weather causes water and melted snow or ice to freeze into place. The warmer temperatures melt the snow, but the weather cycles back around, causing freezing. The constant cycle causes the brick and other construction materials to expand and contract. As the materials change shape, it causes stress and allows water inside. Water can seep inside the brick which weakens the chimney.


Moisture damage causes several problems to your chimney and its foundation. It weakens the brick to the point where brick chips or breaks away from the surface. The moisture rusts any metal surfaces, including the damper. The water breaks down the mortar, which holds the chimney together, and causes cracks in the flue liner. If you ignore the problem, the moisture can even seep into your home and cause mildew, mold and rot on the nearby walls and floors.

Preventing Moisture Damage

Stop damage to your chimney foundation by installing a chimney cap. The cap sits on the top of the chimney and blocks water from getting inside. A chimney cap also prevents animals from gaining access to the chimney and your home. While on the roof, look at the seal on your chimney. Replace the seal with new flashing, which forms a watertight seal on the edges. The Chimney Safety Institute of America recommends sealing your chimney with a waterproof sealant. Even if water and moisture reach the inside of the chimney, the sealant blocks the materials from absorbing the water. A chimney crown works at reducing moisture damage risks by pushing rain off the top of the chimney.


If you see any signs of moss growing on the inside or outside of your chimney, contact a professional. Moss requires a high level of moisture and it indicates that your chimney already suffers from moisture damage. Moss on the inside of the chimney is worse than moss on the outside because it shows a long-term moisture problem. Once the water reaches the inside, it can easily affect the inside of your home.

ReferencesChimney Safety Institute of America: Water Damage & Your Masonry ChimneyElite Chimney Restoration & Maintenance: Water Damage Prevention & RepairThe Chimney Sweep: Chimney Waterproofing – Can Water Damage Really Destroy Your Masonry Chimney?Photo Credit Jupiterimages/ ImagesRead Next:

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