Why is the concrete crown on top of my chimney cracked?
Most crowns crack because the concrete on top of the chimney was poured thin, flat and tight to the brick, with no overhang to throw water clear and no joint allowing the flue tile to move independently. Add water sitting in the cracks, heat moving the flue from the inside, and ordinary settling of the stack, and the hairlines open into gaps.
Phones answered around the clock · free estimate
The nuance is what the crack is doing, not that it exists. A tight hairline in an otherwise sound crown is a sealing job; a crown with open gaps, loose chunks, or brick spalling below it is telling you water has already been getting into the masonry for some time, and that is a repair rather than a touch-up.
Why crowns crack
The crown is the slab across the top of the chimney. Its only job is to shed water off the top of the brickwork and away from the stack. A good one is thick, sloped, extends past the brick by an inch or two with a drip edge underneath, and leaves a small gap around the flue tile so the tile can expand without pushing the slab apart.
Many crowns are none of that. A thin skim of mortar troweled flat across the top is common, and mortar is not concrete — it has little strength in a slab and it cracks as soon as anything moves. Bonded hard to the flue tile, it gets levered apart every time a fire heats the liner and the tile grows.
Once there is a crack, water gets in. Where the weather freezes, that water expands and widens the crack every cycle. Even without freezing, water running through the crown soaks into the brick and mortar below, which is how you end up with spalled brick faces, crumbling joints, a damp smell in the firebox, or stains on the ceiling near the chimney. Flashing at the roofline and a missing cap often contribute to the same water problem, which is why the three get looked at together.
What you can check yourself
Look up from the ground
From the yard, with binoculars if you have them, look at the top of the stack for chunks missing, a visible gap around the flue tile, or a crown sitting flush with the brick instead of overhanging it. Do not go up on the roof.
Look for brick on the ground
Sand, mortar crumbs or brick faces in the gutters, on the roof or in the flower bed below the chimney mean material is coming off the stack. Falling brick is a hazard at ground level, so keep people and cars clear of that side of the house.
Check the ceiling and walls near the chimney
Stains, blistered paint or a damp patch where the chimney passes through tells you water is getting in somewhere above. That may be the crown, the flashing, or both.
Smell the firebox
A damp, musty or sour-smoke smell that gets stronger after rain is a sign water is reaching the inside of the flue. Note when it happens; it helps the technician narrow it down.
Check your alarms
Make sure smoke and carbon monoxide alarms are working on every level. If anyone gets a headache, nausea or dizziness while the fireplace is in use, get everyone outside and call 911.
When to call a technician
Call when you can see open gaps rather than hairlines, when pieces of crown or brick are coming down, when the stack looks like it is leaning, or when you have water showing up inside the house. A leaning stack or one with open gaps is structural, not cosmetic, and it should be looked at before it is used again. If the flue itself is damaged or blocked, stop using the fireplace until someone has inspected it.
One Call Chimney arranges the visit with an independent sweep or mason anywhere in the fifty states. The technician inspects the chimney and gives you the price before any work starts, and you approve it first — a free estimate on every job. Whether any permit applies to crown work or a rebuild varies by state, city and county, so check with your local building department; the technician doing the work can usually tell you what is normal in your area.
What the technician will do
- Inspect the crown and the flue below itThe top of the stack is examined along with the flue, often by camera. Ask to see the footage and ask for the reasoning in writing.
- Repair or recast the crownA sound crown with minor cracking may be repaired and sealed. A failed one is removed and recast with a slope, an overhang past the brick and a drip edge, with a gap left around the flue tile.
- Repoint and replace damaged brickOpen joints are repointed to match the existing work, and spalled brick is cut out and replaced so water stops tracking into the stack.
- Fit a capA cap keeps rain, animals and debris out of the flue and takes load off the new crown.
- Rebuild above the roofline where neededWhere the stack has lost structure, the section above the roofline is taken down and rebuilt rather than patched.
Related questions
- Can a cracked crown be sealed instead of replaced?
- Sometimes. Tight hairlines on a crown that still has thickness, slope and an overhang can often be cleaned and coated with a flexible crown sealer. Once chunks are missing or the slab has broken into pieces, sealing just hides the problem and a recast is the honest fix.
- What drives the cost of crown and masonry repair?
- Access and the height of the stack, whether scaffolding or a lift is needed, how much brick has to be cut out and matched, whether the crown is repaired or fully recast, and whether the flashing, cap or flue show problems too. The technician gives you the price after inspecting, before any work starts.
- Is it safe to use the fireplace with a cracked crown?
- A cracked crown by itself is a water problem rather than a burning hazard, but water damage often reaches the liner and the brickwork inside. If the inspection shows a damaged or blocked flue, or if the stack is unstable, stop using the fireplace until it has been repaired.
- Why is my brick flaking off below the crown?
- That is spalling. Water soaks into the brick through the cracked crown and open joints, then expands and pops the face off. Fixing the crown stops the source; the damaged brick still has to be cut out and replaced.
- How often should the crown be looked at?
- It is normally checked as part of a regular chimney inspection, along with the cap, flashing and flue. Looking at it yearly, and after any severe storm, catches small cracks while they are still cheap to deal with.
Get a technician out
Free estimate. The price is agreed before the work starts.
Or send us a message
Leave your details and what is going on, and someone from the team will call you back.
More from One Call Chimney
Local pages
Answers
Free tool
Keep reading
One Call Chimney arranges the visit; the technician does the work and gives you the price.