The crown is the sloped concrete or mortar slab at the very top of a masonry chimney. Its whole purpose is to shed water away from the flue and the brick below it. When the crown cracks, water gets into the structure, and in Hinsdale, where many chimneys are tall and decades old, a failing crown is one of the most common problems we find.
The good news is that crown trouble is easy to spot once you know what to look for, and catching it early turns an expensive rebuild into a simple sealing job.
Crown versus cap: not the same thing
People mix these up. The cap is the metal cover over the flue opening. The crown is the masonry slab that the cap and flue sit on. The cap keeps water out of the flue, the crown keeps water out of the chimney structure. A chimney needs both in good condition.
The warning signs
From the ground or an upstairs window, look for hairline or wide cracks across the crown, chunks of concrete missing, white chalky staining on the brick below, or plants growing from the top. Inside, a musty smell or staining on the ceiling near the chimney can mean water is already getting through.
- Visible cracks or gaps in the crown slab
- Spalling: flaking or crumbling concrete
- White efflorescence staining on the brick
- Damp patches or odor near the chimney indoors
Why small cracks cascade
Water is patient. A hairline crack lets rain seep in, then winter freezes it, the ice expands, and the crack grows. That water also runs down into the mortar joints and behind the flue liner. What starts as a sealable crack can, over a couple of seasons, become spalled brick and a cracked liner if it is ignored.
Repair or rebuild
Small, tight cracks can be sealed with a flexible crown coating that flexes with temperature swings. A crown that is broken, missing large pieces or sloped the wrong way needs to be removed and recast in proper sloped concrete. We tell you honestly which one your crown needs after a close look.
Many of the large older homes we serve through our chimney sweep service in Hinsdale have crowns that were never sealed, and freeze-thaw cycles find every crack.
Cracked chimney crown in Hinsdale? Get it sealed before winter.
Frequently asked questions
What is the difference between a chimney crown and a cap?
The crown is the masonry slab at the top of the chimney. The cap is the metal cover over the flue. They protect different parts and a chimney needs both.
How long should a chimney crown last?
A properly built and sealed crown can last decades. Many older crowns were poured thin and unsealed, so they crack much sooner in our freeze-thaw climate.
Can you just seal small crown cracks?
Yes. Tight cracks can be sealed with a flexible crown coating. We recommend this early, before water widens the cracks and reaches the brick and liner.
What happens if I ignore a cracked crown?
Water spreads into the mortar, brick and liner. A cheap sealing job can turn into spalled brick and liner replacement, which costs far more.
By Adam Evans, owner of Chimney Sweep Brothers, with 12 years of chimney and venting experience in La Grange and the western suburbs.
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