Spalling brick chimney near top (C) Daniel Friedman Spalling Brick or Concrete Block Chimney Surfaces
Chimney Spalling Inspection, Diagnosis, Repair

  • CHIMNEY SPALLING - CONTENTS: What causes spalling or loss of brick or masonry block surface material from a chimney?Significance of chimney spalling on its exterior. Leaks at chimney shoulders damage building walls & interiors & invite insect pests & rot
  • POST a QUESTION or READ FAQs about the causes and hazards of spalling, flaking, chipping (or cracking) of masonry flues.

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Spalling damage on masonry chimneys: This article defines chimney spalling and describes the causes and significance of spalling on masonry chimney exteriors.

We show examples of different types of brick spalling or concrete block spalling ("cinder block spalling") damage and we explain its causes.

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Causes, Impact & Repair of Spalling Chimney Exterior Surfaces

Spalling brick chimney near top (C) Daniel Friedman Spalling masonry block chimney (C) Daniel Friedman

Spalling describes the chipping off or loss of surface from a masonry material. Spalling can occur on a brick chimney such as the one shown at left, on masonry block chimneys, and on other masonry surfaces such as sidewalks or foundation walls. The chimney is also "supported" by a metal strap tying it to the home.

[Click to enlarge any image]

Spalling brick chimney surface (C) Daniel FriedmanIn our photo at above left you can see that leaks at the chimney top from an improperly sealed chimney crown have sent water into the chimney structure. Not only has the face broken away from some of the bricks, leaving their softer interior exposed to the weather, but also bricks have been dislocated and are being pushed off of the chimney.

Spalling can occur even in warm climates when a masonry product is soft, porous, improperly made, or improperly constructed. But spalling damage is often most severe in northern climates where a freeze-thaw cycle can cause frost to actually break and push off masonry fragments.

Our photo at left shows typical brick chimney spalling - notice that ultimately entire bricks can be lost leaving a hole in the chimney and accelerating water and frost damage.

We sometimes find bricks have been lost entirely from a chimney and we have to ask if the bricks fell into the flue (blocking it and making it unsafe). Our photo at above right shows a spalling concrete block chimney.

A spalled chimney may also have a damaged and unsafe flue.

A detailed inspection of the flue interior is in order. But usually spalling and frost damage occur only on the exterior portions of a chimney exposed to weather, not on the interior portions that run inside of a building.

Cracking spalling chimney exterior (C) Daniel FriedmanWatch out: water and frost damage to masonry chimneys can lead to costly damage, fire and flue gas hazards, and even chimney collapse hazards.


This spalling and cracked masonry chimney exterior was observed near Sharon Ct. and illustrates leaks into and thorugh the chimney structure.

Notice the brown stains exuding from the chimney face about 12 feet below the chimney top? That's a sure indication of water and condensate leaking from the chimney interior out through the masonry structure of the chimney.

The flues in this chimney need to be inspected for safety and the chimney top cap repaired.


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