A crack in the chimney crown (the sloped concrete or mortar surface at the very top of the chimney) is a common maintenance issue but one that should not be overlooked. The crown plays an essential role in shedding water away from the flue and masonry, and when it cracks, it allows water intrusion that can cause progressive deterioration of the chimney system.
Why the Chimney Crown Matters
Water Protection: The crown directs rain and snow melt away from the chimney’s flue and brickwork.
Structural Longevity: Properly sloped, intact crowns prevent moisture from penetrating into mortar joints and masonry.
Weather Resistance: In colder climates, freeze-thaw cycles expand cracks, making them worse with time.
Causes of Cracks in Chimney Crowns
Age and Weathering
Sun exposure, freeze-thaw cycles, and rain eventually wear down mortar and concrete.
Poor Construction
Thin or improperly sloped crowns are more prone to cracking.
Thermal Movement
Heating and cooling cycles cause expansion and contraction, stressing the crown material.
Lack of Reinforcement
Crowns built without wire mesh or proper bonding often develop early cracks.
Consequences of a Cracked Chimney Crown
Moisture Intrusion: Water seeps into the crack, accelerating deterioration of masonry below.
Flue Damage: Moisture entering the flue can rust metal liners or dampers.
Interior Leaks: Persistent water intrusion may eventually cause staining or leaks inside the home.
Worsening Structural Issues: Small cracks grow larger with freeze-thaw action, potentially leading to spalling brick and costly repairs.
Recommended Actions
1. Evaluate the Severity
Hairline cracks: May be sealed with a waterproof, flexible crown sealer.
Large or deep cracks: May require crown resurfacing or replacement.
2. Seal and Protect
Apply a masonry waterproofing sealant designed for chimney crowns.
Ensure the crown has a proper slope to shed water
3. Rebuild if Necessary
Severely deteriorated crowns should be removed and rebuilt with reinforced concrete.
Include wire mesh reinforcement and overhang with a drip edge to prevent runoff down chimney walls.
4. Regular Maintenance
Inspect annually for new or worsening cracks.
Apply sealers every few years to extend service life.
Conclusion
A crack on the chimney crown is a small defect that can quickly become a major problem if ignored. Early repairs—whether sealing, resurfacing, or full replacement—help protect the chimney’s structural integrity, prevent water damage, and extend the lifespan of the entire system.