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CHIMNEY INSPECTION DIAGNOSIS REPAIR
BACKDRAFTING HEATING EQUIPMENT
CARBON MONOXIDE - CO
CHIMNEY CAP & CROWN
CHIMNEY CLEANING PROCEDURES
CHIMNEY COMPONENT DEFINITIONS
CHIMNEY CRACK DETECTION & DIAGNOSIS
CHIMNEY DRAFT & PERFORMANCE
CHIMNEY FIRE ACTION / PREVENTION
CHIMNEY HEIGHT & CLEARANCE CODE
CHIMNEY INSPECTION, FLUE INTERIOR
CHIMNEY LEANING, SEPARATION, MOVEMENT
CHIMNEY REPAIR METHODS
CHIMNEY STAINS & LEAKS
CHIMNEY TYPES & MATERIALS
DIRECT VENTS / SIDE WALL VENTS
DRAFT REGULATOR, DAMPER, BOOSTER
FIRE CLEARANCES INDOORS
FIREPLACES & HEARTHS
FLUE VENT CONNECTORS
MASONRY CHIMNEY GUIDE
METAL CHIMNEYS & FLUES
SAFETY RECALLS CHIMNEYS VENTS HEATERS
SOOT AT CHIMNEY TOP
STAIN DIAGNOSIS on BUILDING EXTERIORS
WOOD, COAL STOVES & FIREPLACES
Diagnose cracks in chimneys:
This article catalogs the types of chimney cracks and movement that may be found in brick, stone, or concrete block chimneys; we describe the inspection and and diagnosis of the cause of each type of chimney cracking and we suggest the probable severity, safety concerns, and chimney repairs that may be necessary.
We include links to additional detailed articles about each type of chimney cracking or movement.
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This article series on chimneys, chimney construction, and chimney safety provide detailed suggestions describing how to perform a thorough visual inspection of chimneys for safety and other defects. Chimney inspection methods and chimney repair methods are also discussed.
Guide to Diagnosing & Evaluating Cracks in Brick Chimneys
Our brick chimney photographs just above illustrate a common (and dangerous) crack pattern found in corbeled (stair-stepped) chimneys where a brick chimney passes through an attic floor and is angled over to exit at the chimney ridge.
At the chimney in our photo at above left, look very closely at the masonry joint where the chimney begins its transition from vertical to angled.
To prevent cracks in a leaned-brick chimney such as this one, the chimney depends on absolutely stable support by the roof framing structure where it passes through the roof to outside. Unless the brick chimney was adequately supported and constructed it may lean, causing the crack pattern we show at above right.
Watch out: often the crack in a leaning brick chimney occurs at the attic floor where the chimney begins its transition from vertical to angled - a spot where the crack may be hard to spot.
See CHIMNEY INSPECTION INDOORS for a discussion of chimney movement that opens a hard-to-find crack where a corbeled brick chimney passes through an attic floor.
List of Typical Causes of Cracks in Brick Masonry Chimneys & Flues
The second cracked chimney at above right is a bit more suspect because we see what might be traces of soot or creosote having washed out through the cracks to the chimney exterior. If this proves to be the case this flue is certainly seriously damaged.
Frost Cracking in Brick Chimneys & Flues - outdoor & indoor evidence of brick chimney damage
Considering that there is a nice thick concrete chimney cap. why do we have this brick movement and mortar-joint cracking?
Perhaps the chimney cap is cracked, flat, not draining, or it was not sealed around the flue, or a rain cap was missing.
See CHIMNEY CAP & CROWN for detailed examples of defects at the chimney top that lead to this type of chimney damage.
Also see Chimney Spalling, Exterior.
At below left we show a very common crack pattern found in brick masonry chimneys & flues - a collection of vertical, diagonal, and even some horizontal chimney cracks that are probably due to a combination of water intrusion and (in freezing climates) frost cracking.
Even if you do not immediately notice the chimney cracks themselves you are likely to spot this chimney damage by the creosote stains carried to the chimney surface by water entry into the chimney flue.
Of course had these cracks and stains been present on a hidden side of the chimney, say between the chimney and a close-by gable-end wall, you'd not see these clues from within the attic.
But inspecting this chimney outside, if it has had no proper rain cap and chimney cap you should be extra alert for water and frost damage to the chimney and its flue.
A second set of clues - water leak stains, may be visible in a fireplace or at a chimney cleanout lower in the building.
Thermal Cracking in Brick Chimneys & Flues May Produce Thin Vertical Openings
At left we show a very common crack pattern found in brick masonry chimneys & flues - a vertical crack that begins in a mortar joint and extends through individual bricks themselves.
Cracked chimney masonry such as shown in the photo of cracks in a brick chimney exterior (at left), may a safety concern if the flue liner or chimney are not intact and fire/gas safe.
The brick chimney crack type shown here is more often caused by thermal expansion (and improper chimney construction) than by frost - frost cracking is often more visually obvious and is often accompanied by brick spalling.
Severe Chimney Cracking - Deteriorated, Collapsing Brick or Masonry Block Chimneys
WARNING: Cracks in a chimney can be very significant and dangerous, risking fire or chimney collapse. Be sure to review the articles
Cracks in Masonry Block or Concrete Block Chimneys
Cracks in a masonry chimney, particularly concrete block chimneys are often caused by
See CRACKED CHIMNEYS, MASONRY BLOCK for details and additional photographs of concrete block chimney cracking.
Chimney Cracks due to Chimney Movement, Tipping, Leaning
Chimneys that lean, curve, bulge, tip, or otherwise move due to footing settlement and tipping or due to failure to secure a tall chimney to the building also may produce both visible cracks on the chimney exterior and hidden cracks and damage to the chimney flue.
The risk of an unsafe chimney flue lies behind our advice that a thorough inspection of the entire chimney flue is necessary when there is any evidence of chimney movement.
See CHIMNEY LEANING, SEPARATION, MOVEMENT: OUTDOORS for details of the detection, analysis, and repair of leaning and tipping chimneys and chimneys that have separated from their building.
Curved Brick Masonry Chimneys
Especially on older buildings using brick chimneys, and more so where the chimney flue is not lined with a modern clay liner, brick chimneys may be seen to curve in one direction.
Often all of the similar chimneys in a neighborhood curve in the same direction. It's not a coincidence. A brick chimney will often curve away from its most weather-exposed side due to sulphation - expanding brick mortar joints caused by the combination of water and sulphur or other minerals.
See CURVED BRICK CHIMNEYS, SULPHATION for further explanation of the cause, significance, and cure of curved brick chimneys.
Continue reading at CRACKED CHIMNEYS, MASONRY BLOCK or select a topic from the index of chimney articles listed above.
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Frequently Asked Questions (FAQs)
(Sept 22, 2011) Fishin said:
How do you repair this? Mine is just like the picture as it goes through the mortar and the brick. It originated from the air vent, I assume because the metal air vent got hot. Thanks.
If a chimney has minor cracks but is structurally sound it may be repaired by re-lining. If the chimney is in danger of collapse it should be removed and replaced. You need an on-site expert to make such a determination. Don't forget to have the flue interior inspected for safety before using such a chimney at all.
Question: smoke coming out of cracks
(Sept 26, 2012) david said:
i have installed about 20 woodburners, and always have them signed off by hetas engineer.... At my own house i have recently fitted wood burner about 5kw, stainless 316/316 flue, pot, ufo cowel. next door is getting smoke done her living room chinmey which has all pot capped on room with pepper posts.
I taped the pepper pots up with gaffa and smoke bombed the fire next door up the flue - it came out of cracks in mortor and around pepper pots still. could it pull down through these cracks and fill the living room next door??? (raised pot from standard to 600mm high laready to try aid the problem.
Watch out: you are describing both a house fire hazard and a chimney operation and draft problem. It's time for a professional chimney sweep's inspection.
Question: gaps at the fireplace sides
(Nov 16, 2014) Jeannie D said:
Last night as my husband built the first wood fire of the season in our fireplace, I noticed a gap between the fire bricks lining the inside of the fire box. The opening was between the bricks on the right side of the fire box and the back of the fire box. When the fire died down, I used the metal fire poker and found I could insert the poker through the gap in the bricks to the metal fire box liner. Is this dangerous? Should I arrange for a fireplace and chimney inspection? My husband doesn't think it's a problem. Thank you.
Watch out: the opening you describe could be a serious fire hazard. It may also introduce draft problems that interfere with chimney operation.
Question: ok to use a cracked chimney pot?
(Nov 30, 2014) Clair said:
I have just re-opened my fireplace to make an open fire. I have a chimney pot to put on but it has a vertical crack in the side ... can this still be used in its current state? if not can it be repaired?
(Nov 30, 2014) DanJoeFriedman (mod) said:
Clair I'd replace the cracked chimney pot rather than trying a repair. You might be able to fill the crack with cement or even an epoxy, but exposed to the weather I'd not expect it to last.
Questions & answers or comments about how to diagnose & repair chimney cracks.
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