If you are facing a chimney rebuild in Milton, here is exactly what the job involves, stage by stage, from the first inspection to clearing up at the end.
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A chimney rebuild is not a small job. It involves scaffold, demolition, bricklaying, leadwork and careful clean-up - and it can take more than one day depending on the size of the stack. Knowing what to expect at each stage means you are not left wondering what is happening on your roof, and it helps you check that the work is being done properly.
This page walks through a chimney rebuild from the first call to the finished stack, based on how a proper job is carried out.
The job starts with a proper inspection. This cannot be done from the ground or from a ladder propped against the gutter. A chimney stack at ridge height needs scaffold access before anyone can give you an accurate picture of what needs doing.
During the initial inspection, the roofer should check:
From this inspection comes a clear decision: is this a repair, a partial rebuild or a full rebuild from roof level? The roofer should tell you which course is the last sound one and why the work starts there. You should get a clear price before anything is agreed.
Once the scope is agreed, scaffold goes up before any work starts. A proper chimney scaffold gives the roofer a stable platform around or adjacent to the stack at a working height, with a safe way to get up and down and a place to stage materials.
The scaffold should not rest on the guttering - it should be footed to the ground or tied to the building structure. A good scaffold takes most of a day to erect and the cost is typically included in the overall job price, though it is worth confirming this upfront.
During the period the scaffold is in place, you will have restricted access around that side of the property. Larger or more complex stacks take longer. The roofer should give you a realistic timeline before work begins.
The first physical work on the chimney is taking it down to the agreed starting course. The pots come off first, carefully if they are being retained, and are set aside or lowered down. The flaunching is broken out. Then the brickwork is taken down course by course.
The demolished material has to come off the roof without damaging the tiles or the roof covering around the stack base. Bricks and rubble are lowered in bags or a rubble chute rather than thrown down - debris dropped on a roof slope can crack tiles and damage guttering. A sheet or scaffold netting below catches dust and fragments.
When the stack is down to the agreed course, the roofer should check that the remaining brickwork is genuinely solid before starting the build-up. Occasionally, what looked sound from above turns out to have soft joints or spalled faces once the top courses are removed, and the starting point drops a course or two lower. This can affect the price, which is why the initial inspection and assessment matters so much.
Before the new brickwork goes up, the lead flashings at the base of the stack are addressed. If they are being replaced, the old lead comes out of the chase cut into the existing brickwork and new lead is prepared. If they are being re-dressed around the new work, they are carefully folded back out of the way while the bricklaying proceeds.
The standard lead detail for a chimney includes step flashings dressed into the brickwork joints up each side of the stack, a back gutter behind the stack where it meets the roof slope uphill of the stack, and an apron flashing across the front. All of these need to be correctly sized for the stack and the roof pitch.
This stage is often done in parallel with the early bricklaying - the roofer builds the stack up a few courses and works the flashing into the joints as they go, rather than leaving it all to the end when the stack is already at full height.
The new brickwork is laid course by course. The brick should match the existing stack as closely as possible in size, colour and density. The mortar mix should suit the brick - a lime-based or weaker sand-and-cement mix for softer older bricks, a standard mix for harder modern ones. Hard cement mortar used on a soft brick stack will crack within a few years.
Each course is checked for level and plumb as it goes up. A chimney that finishes even slightly out of plumb looks wrong and can create uneven loading on the lower courses. The joints are struck off neatly as the work proceeds rather than left and tooled afterwards, which gives a better bond and a cleaner finish.
Where the rebuild is more than three or four courses high, the roofer may need to leave the new mortar to go off overnight before adding further courses - fresh mortar needs time to firm up before it can take the weight of further brickwork above it.
Once the stack is up to the correct height, the chimney pots are bedded on the top course. Each pot sits in a bed of mortar on the last course of brickwork. Where a stack has two or more pots, they should be evenly spaced and at consistent height.
The flaunching is then laid around the pot bases. It is a sloped mortar fillet, running from the base of the pot down to the outer edge of the top brick course, typically at around 45 degrees. The slope is what sheds the water. Flat or hollow flaunching holds water and deteriorates quickly.
Where pots are being capped rather than left open, a ventilated cap is fitted over the pot before the flaunching goes on, or a lead cap is dressed after. An unventilated sealed cap on an unused flue traps moisture and should be avoided.
With the stack complete, the lead flashings are dressed into their final position. Step flashings are wedged and pointed into the chases cut in the brickwork joints. The pointing should be a mortar mix, not sealant - sealant is a temporary fix and will need redoing within a few years. The back gutter and apron are finished and any overlap joints dressed neatly.
The roofer should check that no water can get behind the flashing at any point and that the lead is not bridging the tile surface in a way that prevents movement. A finished lead flashing should look neat and sit flat without creasing or puckering.
Before the scaffold comes down, the roofer should carry out a final check of the full stack - plumb, pointing quality, flaunching slope, pot seating and flashings. Any remedial work can be done while the platform is still in place. This is the right moment to deal with anything, not after the scaffold is away.
The roof slope around the stack base is checked for any tile damage or displaced slates that occurred during the work. Debris from the demolished brickwork is cleared from the scaffold boards and the surrounding roof area. All rubble and waste material is taken away - you should not be left with a pile of old bricks or broken mortar on your property.
The scaffold then comes down, typically on the last day of the job. Once it is clear, the whole finished stack is visible from the ground for the first time and the homeowner can see the completed work.
If you can see signs of deterioration on a chimney stack at your Milton property - leaning, crumbling mortar, loose pots, damp on internal chimney breast walls - call Cambridge Roofers to arrange an inspection. The roofer should get on the scaffold, give you a clear picture of what the stack needs and a straightforward price for the work before anything starts.
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