Chimney repointing in Lewisham
Pointing is the sacrificial layer that keeps water out of a chimney. When it fails, everything behind it starts to suffer — which is why repointing at the right moment is one of the cheapest pieces of roof maintenance there is.
Repointing means raking out the failed mortar from the joints and replacing it with fresh mortar. On a chimney it is more demanding than on a wall at ground level, because the stack is exposed on every face, is usually only reachable from scaffolding, and is often built from soft brick that will not tolerate the wrong mix.
What failed pointing looks like
- Joints that are visibly recessed compared with the brick face
- Mortar you can crumble or rake out with a finger or a key
- Sand or grit collecting in the gutter below the stack
- Dark, permanently damp banding on the brickwork
- Moss, or small plants growing out of the joints
- Daylight visible through joints when viewed from the side
- Damp appearing on a chimney breast indoors after driving rain
- Previous pointing standing proud of the brick, cracked and lifting away
Why chimney pointing fails faster than the rest of the house
A chimney stack gets weather from all four sides and from above. Unlike a wall, it has no roof over it and no shelter from adjacent structures. Rain driven onto it does not run off the way it does down a slope — it sits in the joints. In winter that water freezes, expands and progressively breaks the mortar apart.
On a disused flue it is worse again. A working chimney warms up and dries out from the inside. Once the flue is closed off — as most Lewisham stacks were when houses moved to gas and central heating — that drying stops, and the masonry stays wet for longer after every rainfall.
The mortar matters more than most people expect. Original lime mortar is softer than the brick around it, and that is deliberate: it takes the movement and the moisture damage so the bricks do not. Repointing a soft London stock stack in hard cement reverses that relationship — the joints become the strongest part, and water leaves through the brick faces instead, blowing them off in frost. We assess the existing brick and mortar and specify a mix suited to what is actually there.
How the work is done
- Assessment. How deep the erosion goes, what the existing mortar is, and whether the brick faces are still sound. If the bricks have spalled through, repointing alone will not fix it — that is a rebuild conversation.
- Access. Scaffolding to give a safe working platform with reach to every face of the stack.
- Raking out. Removing the failed mortar to a proper depth — generally at least twice the joint width — so the new mortar has something to key into. Shallow "smearing" over old mortar is the most common bad practice we are called back to correct; it looks fine for a season and then falls out.
- Cleaning and preparation. Joints brushed out and dampened so the new mortar cures properly rather than drying out too fast.
- Repointing. Fresh mortar worked into the joints in layers where the joints are deep, then finished to a profile that sheds water and matches the character of the brickwork.
- Checking the rest. While the scaffold is up, the flaunching, pots and flashing are checked. It is rarely economic to bring scaffolding back for those separately.
When repointing is not the answer
We would rather tell you this before you pay for it. Repointing will not solve the problem when:
- The brick faces have spalled. Once the outer skin has blown, there is no sound face to point against and the stack will keep deteriorating. See spalling brickwork and lime mortar for why this happens and what it needs instead.
- The stack is leaning or has moved. Pointing does not add structural strength. See stack repair and rebuild.
- The leak is at the flashing. A very common misdiagnosis. If water is entering at the junction with the roof, repointing the stack above it changes nothing. See flashing repair.
- The flaunching has failed. Water entering through a cracked mortar cap runs down inside the stack, so the joints stay wet however well they are pointed.
Repointing the whole stack, or part of it?
Erosion is rarely even. The weather side — on most Lewisham roofs, the south-west face — will usually be noticeably worse than the sheltered side. It can be tempting to do only the bad face. In practice, once scaffolding is up, the additional cost of pointing all faces is modest compared with the cost of returning in a few years to do the rest. We will give you both options and be straight about the difference.
Not sure whether yours needs repointing?
A photograph taken from an upstairs window, or from the garden with a zoom, usually shows us enough to say whether the joints have gone.
Repointing questions
How often does a chimney need repointing?
There is no fixed interval — it depends on the original mortar, the exposure of the stack and the quality of any previous work. Well-executed pointing in an appropriate mix on a sheltered stack can last several decades. Poorly done pointing, or the wrong mix on soft brick, can fail in a handful of years.
Can repointing be done in winter?
It can, but not in a hard frost and not when frost is forecast before the mortar has cured — new mortar that freezes before it sets is ruined. In practice this means we watch the forecast rather than the calendar. Autumn and spring are usually straightforward.
Will the new pointing match the existing brickwork?
That is the aim, and it is worth caring about on a period property. Mortar colour and joint profile both affect how a stack looks from the street. Where a stack is only partly repointed, some difference in tone between new and weathered mortar is normal at first and reduces as the new work weathers.
Is repointing cheaper than rebuilding?
Yes, substantially — provided the brickwork is sound enough for it to be the right answer. The cost that is common to both is the scaffolding, which is why we look at everything while access is up. See the cost page for what drives the difference.