Can a leaning stack be repointed or does it need rebuilding?

A lean means the joints have already expanded or failed, so pointing does not restore the geometry. Leaning stacks are normally taken down to sound brickwork and rebuilt. Repointing is the answer where the stack is plumb and the joints have simply eroded.

Should I just remove the chimney instead?

It is a common choice on a stack serving no working fire, and it removes the maintenance. It also needs the roof made good properly and the flue dealt with below, and taking a stack down changes how the roof and the wall below are loaded, so it is planned rather than improvised.

Why is my chimney worse than the rest of the house?

Because it is exposed on four sides, gets no warmth from inside once the fire is unused, and has had flue salts drawn through its brickwork for decades. Stacks routinely need attention two or three times over the life of the walls below them.

The chimney only leaks when it rains — is that the brickwork?

Not necessarily. Water getting in at the junction between stack and roof is usually failed lead flashing, which is a roofer's work. Cracked flaunching at the top and open joints in the stack are the bricklayer's side. Both produce a stain in the same place, so the detail is inspected as a whole.

High risk

Updated 30 August 2026

Crumbling Or Leaning Chimney Stack

The brickwork above the roof line has lost its mortar, shed brick faces, or started to lean to one side.

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What's happening?

A chimney stack is the most punished masonry on a house. It is exposed on all four sides with no shelter, it gets no warmth from the building below once the fire stops being used, and it is soaked and frozen more often than any wall. On top of that, a stack that served an open fire for decades has flue gases and salts drawn through its brickwork from the inside, which attacks the mortar from within. That combination is why stacks decay long before the walls beneath them. A lean has its own explanation: sulphate attack in the mortar on the side that stays wettest makes those joints expand, so the stack grows fractionally taller on one face and bends away from the prevailing weather.

What usually causes it?

Sulphate attack in the mortar from flue condensates and salts, expanding the joints on the wettest face
Freeze-thaw damage on brickwork that is exposed on every side and never warmed from within
Flaunching around the pots cracked or missing, letting water straight into the top of the stack
Lead flashings, apron or soakers at the roof junction failed, so water runs down inside the stack
Mortar joints eroded through so far that courses are no longer bonded
An unlined or disused flue holding damp inside the stack with no through draught to dry it
The stack rebuilt or capped earlier in a cement mortar that cannot cope with the salts present

Is it dangerous?

Yes — this is high risk, and the reason is height. Brickwork falling from above the roof line lands on a roof, a garden or a pavement, and it can go through a roof covering or a conservatory on the way. Treat it as urgent if the stack leans, if a course has moved, if pots are loose or if you are finding brick debris or mortar in the gutters. All work on it happens at height, and HSE guidance on work at height applies, so the access matters as much as the brickwork. A stack serving a working flue also has a combustion side to it: if the flue is in use, have the appliance and the flue checked once the masonry is made good.

Can I fix it myself?

No. There is no safe version of a homeowner working on a chimney stack — it needs a scaffold or a tower, and the material being worked on is precisely the material that is already loose. What you can do is check it from the ground with binoculars, photograph it against a vertical line such as a downpipe or a corner so a lean is measurable, and look in the gutters for spalled fragments and mortar grit, which is often the first evidence. If there is debris on the roof or the ground, keep the area below it clear and get it looked at rather than waiting for the next gale.

When should you call a bricklayer?

Call a bricklayer or roofer promptly if the stack leans, if pots look unstable, if mortar has gone from the joints, or if there is brick debris in the gutters. Call urgently after high winds, or if anything has already fallen. Where the problem is water getting in at the roof junction rather than the brickwork itself, that is flashing and belongs to a roofer, and it is worth having both looked at together because the two faults feed each other.

What will the bricklayer actually do?

Inspect the stack from a scaffold or tower, checking plumb, joint depth, pot stability and the flaunching
Repoint the stack in a mortar suited to a saturated, salt-laden exposure rather than a general-purpose mix
Take down and rebuild the stack, or its upper courses, where the joints or bricks have gone past pointing
Renew the flaunching around the pots and reset or replace unstable pots
Fit a damp proof course and a suitable cap or cowl where a disused flue is holding water in the stack
Coordinate the lead flashings and roof junction with a roofer so the whole detail sheds water

Frequently asked questions

We’re happy to answer all your questions.

Sources & References

Crumbling Mortar Between BricksCaution Spalling Or Crumbling Brick FacesCaution Chimney Leaking When It RainsHigh risk Chimney Breast Removed Without SupportHigh risk

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