Masonry Chimney Inspection and Common Defects

A masonry chimney is constantly exposed to rain, snow, moisture and repeated freezing and thawing cycles. Even small cracks in the chimney crown, mortar joints or masonry can allow water to enter the structure. As this moisture freezes and expands, deterioration can gradually become more severe, damaging bricks, mortar and other chimney components. A masonry chimney inspection can identify visible signs of deterioration before they develop into more serious structural or safety concerns.

During a masonry chimney inspection, visible signs of moisture penetration, cracking, deteriorated mortar and damaged masonry should be carefully examined.

Where jointed precast concrete or masonry chimney caps are installed, the Building Code requires flashing beneath the cap, extending from the chimney liner to the drip edge. This prevents water from penetrating through the joints and entering the masonry below.

During a masonry chimney inspection, the condition of the chimney crown, mortar joints, drip edge and accessible masonry should be examined for cracking, deterioration and evidence of moisture penetration. Damaged chimney crowns are a common source of water infiltration and can lead to expensive repairs when left unattended.

Masonry chimneys are heavy structures that require adequate support. Settlement or movement of the chimney foundation can cause cracking, separation or leaning of the chimney. Cracks may develop in the masonry itself or where the chimney meets the exterior wall of the house. Water and snow can also enter gaps between the chimney masonry and exterior siding. Repeated freezing and thawing of this trapped moisture can contribute to further separation and movement of the chimney.
Visible leaning, displaced bricks, widening cracks or separation between the chimney and building can indicate movement that requires further investigation. Significant structural movement may affect both the stability of the chimney and the integrity of the flue system. During a masonry chimney inspection, these conditions should be identified so that appropriate repairs or further evaluation can be recommended.

Common signs of masonry chimney deterioration include cracked or missing mortar joints, spalling bricks, loose masonry, damaged chimney crowns and staining caused by water penetration. White powdery deposits, known as efflorescence, can also appear on the masonry where moisture has moved through the brick or mortar and deposited salts on the surface.
Other warning signs can include leaning or separation from the house, deteriorated flashing, cracked flue tiles and pieces of masonry or mortar collecting around the base of the chimney or fireplace. Water stains on nearby walls or ceilings may also indicate that moisture is entering around or through the chimney. Identifying these conditions early can help prevent relatively minor defects from developing into more extensive chimney repairs.

Masonry chimney defects can become progressively worse when exposed to continued moisture, freezing temperatures and repeated heating and cooling. A small crack in a chimney crown or mortar joint may initially appear minor, but once water enters the masonry, freeze-thaw cycles can enlarge the opening and accelerate deterioration.
Damaged masonry can eventually lead to loose or spalling bricks, deteriorated mortar joints, water leakage and damage to the chimney's flue system. Problems affecting the flue liner can also reduce the protection between hot combustion gases and surrounding building materials. Identifying and repairing chimney defects early can help prevent more extensive and costly repairs while maintaining the safe operation of the fireplace or wood-burning appliance.

A masonry chimney is an important part of a wood-burning system and should be examined for visible defects that could affect its condition or safe operation. Cracked masonry, deteriorated mortar, damaged flue liners, water penetration and structural movement are among the conditions that may be identified during an inspection.
For more information about wood-burning appliances and chimney inspections, visit our WETT Inspections Barrie page or review our WETT Inspection Information page.