Chimney & Fireplace Problems
Cracked Chimney
Not all chimney cracks mean the same thing. Where the crack runs, and whether it follows the joints or goes through the brick, tells you most of what you need to know.
What Kind of Crack Are You Looking At?
The most useful distinction is whether the crack follows the mortar joints or cuts through the brick itself. A crack that steps its way along the joints is taking the path of least resistance through the weakest material, which is what mortar is designed to be. A crack that goes straight through brick faces has more force behind it.
The second distinction is direction. Horizontal and stepped cracks along joints are usually weathering and mortar failure. A single vertical crack running up a face, or a crack that is wider at one end than the other, suggests movement rather than wear.
And the third is whether the crack is inside the flue or outside on the stack. Cracks in clay flue tiles are a liner problem, invisible from outside, and considerably more consequential than cracks in the brickwork.
What Causes Chimney Cracks
In rough order of how often each turns out to be the explanation.
Freeze-thaw on wet masonry
The dominant cause in Connecticut. Water in a joint freezes, expands, and opens it further every winter.
A failed crown letting water into the stack
Cracking in the upper courses very often starts at the top and works down.
Thermal cycling
Heating and cooling over decades, particularly where a flue is used hard.
Settlement or movement
Less common, more serious. Usually produces a single continuous crack rather than stepped joint failure.
A chimney fire
Cracks clay flue tiles at temperatures a normal fire never reaches. Invisible from outside.
Impact
A fallen limb or storm damage. Usually obvious, and usually localised.
Which Cracks Are Actually Serious
Stepped cracking along mortar joints on the exposed courses is the most common thing people photograph, and it is ordinary weathering. It needs repointing and it is not an emergency.
What warrants faster attention: a stack that is visibly out of plumb, leaning or bowing; a crack that has visibly widened over a season; a crack wide enough to see daylight through; and any cracking accompanied by masonry arriving on the roof or in the garden.
And separately from all of it, cracks inside the flue. A cracked liner is the most consequential crack a chimney can have, and the only way to know about it is to look up the flue.
If a carbon monoxide alarm sounds, or you can see daylight through the chimney from inside the firebox, stop using the fireplace and get it looked at before lighting it again.
What Each One Needs
Stepped joint cracking is repointed — the failed mortar cut out to depth and replaced in a mix matched to the masonry. On older Connecticut chimneys that mix matters enormously, because hard modern cement in soft old joints takes the brick face off at the next freeze.
Cracked brick faces are cut out and replaced individually. Widespread cracking across a whole area is where the rebuild conversation starts, and a partial rebuild of the top courses is far more common than a full one.
A cracked crown is repaired or recast, and doing that is usually what stops the cracking below it from continuing. A cracked liner is repaired in place if the damage is isolated, and relined if it is not.
Frequently Asked Questions
Are some chimney cracks normal?
Stepped cracking along mortar joints on exposed courses is ordinary weathering on an older chimney, and it is what repointing is for. It is not something to ignore indefinitely, but it is not an emergency either.
There is one long vertical crack. Is that worse?
It can be. A single continuous crack cutting through brick rather than stepping along joints suggests movement rather than weathering, and that warrants a proper look rather than a photograph.
How do I know if a crack is getting worse?
Photograph it against something fixed and look again after a season. A crack that has visibly widened over a few months is behaving differently from one that has looked the same for years.
Could there be cracks I cannot see?
Yes, and they are the ones that matter most. Cracked clay flue tiles are invisible from outside and from the room, and they are the most consequential defect a chimney can have. That is what an inspection establishes.
Does a cracked chimney need rebuilding?
Usually not. Most cracking is in the mortar and the most exposed courses, which is repointing and brick replacement. Rebuilding is for structural failure — a stack out of plumb, or deterioration deep and widespread enough that replacing individual bricks means replacing most of them.
What Cracking Usually Needs
Chimney Masonry Repair
Brick and mortar work on the stack.
Chimney Tuckpointing
Cutting out and replacing failed joints.
Chimney Crown Repair
Very often where the cracking below it started.
Chimney Inspection
The only way to know about cracks inside the flue.
Chimney Rebuild
Where the deterioration has gone past repair.
Spalling Chimney Brick
What happens after the joints have been open a while.
Request a Free Estimate
Cracks in Your Chimney?
Send a photograph from the ground. Whether a crack follows the joints or cuts through the brick is usually readable from one, and it changes the answer completely.
- Tell us the symptom, not the service
- No quote before someone has looked
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Describe the Problem
A few details is all we need to get started.