In short
A chimney leaks through its joints, not its bricks. The usual causes are lead flashing that has pulled out of the brickwork, cracked flaunching around the pots, mortar joints that have washed out so far the brick holds water, or an open pot letting rain straight down the flue. Damp on the chimney breast inside, worst after driving rain, is the giveaway.
This is a job for our Chimney repointing service.
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Four ways in
A brick stack stands above the roof in the full weather with no protection from anything. On the chimneys we repair between King's Lynn and Swaffham the water is getting in at one of these points:
- The flashing. Lead step flashing should be chased into a mortar joint and wedged. Flashing that was bedded on the surface, or is code 3 lead where it should be code 4, lifts and lets water run down behind it.
- The flaunching. This is the mortar cap the pots sit in. It cracks with frost, and once cracked it holds water against the top course of brick.
- The pointing. Mortar joints erode from the weather side. Once they are recessed the brick face gets saturated and the damp comes through the stack into the chimney breast.
- The pot. An open flue on a fireplace that is no longer used takes rain straight down. A cowl or a capped pot with a vent fixes that.
Reading the damp patch
| Where it shows | Most likely cause |
|---|---|
| Ceiling either side of the breast, after rain | Flashing or back gutter |
| High on the breast, worst on the weather side | Pointing |
| Damp in the fireplace, smells sooty | Open pot or cracked flaunching |
| Brown tide marks on the plaster | Salts from a stack that has been wet a long time |
Why it gets worse fast on the coast
Salt air and driving rain off The Wash strip lime mortar out of exposed joints quicker than inland. A stack at Hunstanton or Heacham will need pointing sooner than the same stack in Swaffham. If the joints are recessed deeper than the width of your finger, the stack is holding water.
What it costs to fix
MyJobQuote's 2026 guide puts repointing a full chimney stack between £450 and £1,200, a flaunching repair at £150 to £300, and a lead flashing repair at £150 to £350, with scaffolding adding £300 to £600 where a ladder will not do. Access decides more than the work: a low stack on a bungalow we can reach from a tower, a tall stack on a three-storey house needs a scaffold.
Repair or take it down?
If the stack is leaning, the brick faces have spalled, or the mortar is gone to the depth of a brick, repointing is putting new mortar into a stack that is failing. In that case we would rather take it down to below the roofline and tile over than sell you a repoint that fails in two winters. We will tell you which one we are looking at from the photographs before you decide.
