The Effects of the Freeze/Thaw Cycle on Your Chimney

When your masonry chimney was initially constructed, it was designed to last decades. However, rain, wind, extreme swings in temperature, and other weather events can accelerate its deterioration, exposing the porous structure to moisture. While age and cold weather are mostly to blame, a lack of routine inspections and maintenance is also a contributing factor.

Repairs to Chimney Damage Amherst, NHWinter Weather Damage

As precipitation saturates the porous brick masonry, the moisture will seep through any cracks or crevices. It absorbs the moisture softening the concrete, sand, and lime that mostly comprise of the bricks. It also weakens the mortar that holds the bricks in place. Its erosion leaves gaps in the mortar joints between the brickwork.

Freeze-Thaw Cycle

When cold winter temperatures fall below freezing, the moisture that has already been absorbed turns to ice. The expanding ice crystals cause the softened material to crack and crumble. Rising temperatures thaw the ice crystals trapped inside the bricks. More winter precipitation fills these cracks and crevices where it will crystalize once again when the temperature dips below freezing. The continuous freeze-thaw cycle further widens the cracks and erodes the mortar resulting in larger pieces of chipped bricks. As the damage progresses, the sight of missing bricks in the chimney is evident. It can even lead to a complete chimney collapse.

Chimney Crown

Winter weather can also damage the chimney crown, especially if the chimney lacks a chimney cap. Heavy rain and snow can cause hairline cracks in its surface. The freeze-thaw cycle can accelerate the damage and allow moisture to seep in between the flue and interior walls. 


The flashing can also be at risk for winter weather damage. The thin metal strip seals the gaps between the chimney and the roofline. When the flashing is warped or damaged, moisture can penetrate through any gaps. Spotting water stains on the ceiling near the fireplace is often an indicator of a flashing problem rather than a roof leak. Repair or replace the flashing as soon as possible to avoid roof damage.

chimney Inspection Concord, NHChimney Inspection

The Chimney Safety Institute of America (CSIA) recommends annual chimney inspections. An annual chimney inspection is your first line of defense to protect your chimney from the damaging effects of winter weather. The review will assess the condition of your chimney and recommend the necessary repairs to any damaged areas.


Waterproofing the chimney can also help prevent water intrusion. It is necessary first to repair any cracked or missing bricks and mortar, otherwise, waterproofing will not be very useful. For best results, it is recommended that only a licensed chimney professional should apply the sealant. Chimney professionals use a vapor-permeable sealant that shields against rain or snow while allowing the masonry to breathe. Other types of water sealants can trap moisture further deteriorating the brickwork.