Cambridge Roofers carries out chimney rebuilds for homeowners in Potton, and this page walks you through exactly what the job involves from start to finish.
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A chimney rebuild is not a small job. Scaffold goes up, brickwork comes down, and for a few days your home has a significant piece of work on its roof. Homeowners who understand what should happen at each stage are in a much better position to ask the right questions and spot when something is being skipped.
The process below covers a full chimney rebuild from roof level. Some jobs are lighter - a partial rebuild of the pot section and flaunching only - but the same principles apply.
The starting point is working out what the stack actually needs. From ground level you can spot obvious signs - a leaning pot, visible gaps in the mortar, white salt deposits on the brickwork, damp patches on an interior wall near the chimney breast. But a ground-level look is not enough to specify the job accurately.
A proper assessment is done from scaffold or from the roof, where the roofer can press the mortar joints, check whether the brickwork is loose or moving, look behind the flashing line, and assess the condition of the flaunching and the flue pots at close range. This is the only way to establish where the sound brickwork ends and where the rebuild needs to start.
At this stage a good roofer will also check the condition of the lead flashings, the roof covering immediately around the chimney base, and whether the stack has been previously repaired in a way that may have caused additional problems - hard cement repointing over soft original brick, for example, is a common issue that is only obvious up close.
All chimney rebuild work should be done from scaffold. A chimney stack is at the highest and most exposed point of the building, and the work involves handling heavy brickwork and lead. Roof ladders or working from a ladder at height is not safe for this type of job and does not give the roofer a stable platform to do the work properly.
For most domestic chimney rebuilds in Potton and the surrounding area, scaffold is typically a tower or a tied frame around the stack with a working platform at roof level. On terrace properties or where the stack is on a party wall, the scaffold may need to span from the ridge. The scaffold hire is a cost that should be included transparently in any quote.
Once the platform is in place, the existing pots are lifted off and set aside if they are being re-used, or lowered down for disposal. The flaunching mortar is broken away, then the brickwork is carefully taken down course by course to the point where it is still solid and sound.
Where the rebuild is from roof level, the brickwork is taken down to the point where the stack exits the roof covering. The lead flashings are stripped back at this stage. Old mortar is cleaned off the top course that will form the base of the new work, and the surface is checked to make sure it is stable enough to build on.
Brick debris is usually lowered in a skip bag or passed down by hand to a colleague below rather than dropped. If a skip is required for larger volumes of material, this should be factored into the quote.
New brickwork is laid from the sound base upward, course by course, using a mortar mix appropriate to the brick type. On older properties with original softer brick below, a lime-based mortar is the right choice - it is more flexible and breathable than a hard sand-and-cement mix, which can trap moisture and cause the original brickwork to spall. On modern properties a sand-and-cement mix is standard.
The brickwork is built plumb and level, with consistent joint thickness. Each course is checked with a level as the work progresses. The stack should be built to match the original profile - any change in size or profile affects both the appearance and the way the chimney weathers.
Bed joints at regular intervals are raked back slightly as the work progresses to accept the lead flashings at a later stage. This is done as the brickwork is built, not chased in afterwards, as raking out existing joints in new brickwork risks disturbing it before it has fully set.
Once the brickwork has reached the correct height, the pots are set on a freshly laid mortar bed and the flaunching is formed around them. Flaunching is the sloped mortar collar at the top of the stack - it holds the pots firmly in place and sheds water away from the top of the brickwork. It is shaped in a smooth slope falling away from the pots to the edge of the stack.
The flaunching needs to be worked to a consistent profile and finished neatly so that water does not pond anywhere on the top surface. It should be allowed to go off (begin to set) at the correct rate - covering it in cold weather if necessary to prevent it drying too quickly and cracking.
With the brickwork set, the lead flashings are fitted. This is a skilled part of the job. Lead step flashings are cut and dressed into the raked mortar joints up each side of the stack. At the high side (the side where the roof slope runs up toward the chimney) a lead back gutter is formed to collect water and channel it away. At the low side, an apron flashing is dressed down over the roof covering.
The lead is fixed into the mortar joints and then pointed in with fresh mortar to hold it securely. Each section of lead overlaps the one below it so there is no joint that water can track back through. The finished flashings should sit tightly against the brickwork with no visible gaps and no sealant used as a substitute for proper dressing.
Once the flashings are in, any remaining external joints are pointed to match the style used on the rest of the stack or the property where possible. The finish should be consistent and neat. For lime mortar jobs, the finished pointing needs time to cure properly - this should not be rushed in cold or wet conditions.
Any surface of the stack that has previous repointing in a hard cement mix may need attention at the joints to prevent the existing hard mortar trapping moisture against the new brickwork.
Before the scaffold comes down, the finished work is checked from the platform. This is the time to confirm the flashing sits correctly, the flaunching shows no cracks from curing, the pots are stable, and all joints are fully pointed. The scaffold platform is cleared of all brick debris and waste materials.
After the scaffold is struck, the area around the base of the building is cleared of any debris that has come down during the work. The job is not finished until the site is left as it was found.
As a rough guide, a full chimney rebuild from roof level on a standard domestic stack - including scaffold, new brickwork, flaunching and lead flashings - typically costs between £1,500 and £3,500. A partial repair covering just the flaunching, repointing and re-setting pots usually falls between £300 and £600. Height, access, the amount of brickwork involved and the lead work required all affect the final figure.
We cover Potton and the surrounding area for chimney rebuilds. If you want a straight answer about what your stack needs, call us to book a chimney survey from scaffold and we will take you through what the job involves before any work starts.
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Call any time. Calls are answered day and night and passed straight to our roofers.
