Symptoms
- Visible cracks in the concrete cap on top of the chimney
- Water staining on the chimney's interior or exterior below the crown
- Crumbling mortar or spalling brick near the top of the chimney
Likely causes
- CommonNormal aging and weather cycling of the concreteSun, rain, and freeze-thaw cycles crack crowns over years, especially poorly mixed or thin ones.
- CommonOriginally undersized or poorly formed crownMany crowns are built too thin or without proper reinforcement, cracking sooner than they should.
- PossibleWater freezing in an existing small crack and expanding itFreeze-thaw cycling turns small cracks into bigger ones over successive winters.
What to do
- View the crown from the ground with binoculars or from a safely accessible vantage point to assess crack size and extent.
- Note whether cracking is minor surface crazing or larger structural cracks with separation.
- For small cracks, a crown-specific sealant can be applied as a temporary measure to slow water entry.
- Check the chimney interior for related water staining or damage that the cracked crown may be causing.
- Have a chimney professional apply a proper crown sealant or rebuild the crown for larger or deeper cracks.
- Combine crown repair with a chimney cap installation if one is missing, since the cap protects the flue while the crown protects the top surface.
- Schedule periodic chimney inspections to catch new cracking early.
Tools and parts
- Binoculars
- Ladder (roof access with caution)
Chimney crown sealantSearch: “chimney crown coat sealant”
When to call a pro
Call a chimney mason for crown repair or rebuilding, especially for cracks with visible separation.
Safety
Use caution
Chimney top work carries significant fall risk; use caution and consider a professional for roof-level access.