The short answer
A chimney needs repointing when the mortar between its bricks has eroded, cracked or fallen out, letting rain soak into the stack. Repointing means raking out the loose mortar to a consistent depth and filling the joints with fresh mortar of a suitable mix, finished to match the rest of the house. Because a stack is exposed to weather on all sides, it usually wears faster than the walls below, and leaving it can lead to damp inside, loose bricks and in bad cases a rebuild.
Signs it needs doing
Look for joints that are recessed well back from the brick face, sand or mortar on the roof or in the gutters, plants growing from the stack, or damp patches on chimney breasts inside, especially after heavy rain. A stack that leans, has cracked bricks or has loose pots needs more than repointing and should be checked properly before anyone quotes.
How it is done
Safe access comes first, usually scaffolding with a platform around the stack. The old mortar is raked out by hand or with a suitable tool, deep enough for the new mortar to key in without damaging the brick edges. The joints are brushed out and dampened so the new mortar does not dry too fast. Fresh mortar is pressed in and finished with the joint profile that matches the house. Work stops in frost or heavy rain because new mortar needs time to cure.
Why the mortar mix matters
Mortar should be slightly weaker and more porous than the bricks, so moisture escapes through the joints rather than the brick face. Very hard cement-rich mortar on older soft bricks traps water, and the brick faces then crumble in frost. On older houses a lime-based mortar is often the right choice. Matching the colour with the right sand keeps the repair from standing out.
What to check while the scaffold is up
Since access is the costly part, it makes sense to inspect everything at once: the flaunching (the mortar cap around the pots), the pots themselves, the lead flashings where the stack meets the roof, any cracked or spalled bricks, and the cowls. Doing these together avoids paying for access twice.
Repoint, repair or rebuild?
If the bricks are sound and only the joints have failed, repointing is enough. If some bricks are cracked or have lost their faces, those are cut out and replaced as part of the job. If the stack is leaning or badly frost-damaged, taking it down and rebuilding from sound brickwork may be the only lasting fix. Our chimney repair guide covers those bigger jobs.
Why stacks wear faster than walls
A chimney stands above the roof with no eaves or neighbouring walls to shelter it. Wind drives rain into every face, and the brickwork freezes and thaws more often than the walls below. On stacks that are no longer used, the flue stays cold and damp, which adds to the wear. Capping unused flues while leaving ventilation, and keeping the flaunching sound so water runs off the top, both help new pointing last longer.
About us
D & A Brickwork & Building is a family-run firm based in Bidwell, Dunstable. We have more than 26 years of building experience, our bricklaying is NVQ Level 2 qualified, we are members of the Federation of Master Builders and we are fully insured. Estimates are free and follow a visit to see the job.
Chimney work and repointing are part of our bricklaying service, alongside brick matching and repairs.
Need more than repointing? See our chimney repairs and rebuilds page.
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Questions people ask
How do I know if my chimney needs repointing?
Recessed or crumbling joints, mortar in the gutters, plants in the stack or damp on the chimney breast inside are the usual signs.
Can a chimney be repointed without scaffolding?
Safe access is needed to work on all sides of the stack, and in most cases that means scaffolding.
Should I use lime mortar on my chimney?
On older houses with softer bricks, a lime-based mortar is often better because it lets moisture escape. A builder should match the mortar to the brick.
Does repointing fix a leaning chimney?
No. A leaning stack needs inspecting and may need partial or full rebuilding.