How a Chimney Rebuild Is Done, Course by Course

Scaffold and protection first

Nothing starts on a rebuild until the access is right. A stack stands at the highest point of the roof, so the scaffold has to reach above it, with a working platform at head height rather than at the knees. Boards run all round, and edge protection stops tools and bricks rolling off. Where a path, conservatory or neighbouring roof sits underneath, a debris net or fan goes on to catch anything that falls.

Then comes the protection of the house itself. Roof slopes around the stack are covered so that falling mortar does not mark or crack tiles and slates. Drives and gardens are sheeted where work is above them. Windows and vents below the stack are closed or covered, because brick dust is fine and finds its way into every gap.

On some properties the scaffold needs a licence or permission from the local council if it stands on a footway or road. That is a matter for the council, not a point of legal advice from us, and your quotation will say who arranges it. Our guide to What Should Be on a Chimney Repair Quotation? lists what to look for on such points.

Taking down, and what is kept

Taking down is done by hand, a course at a time, from the top. As each brick comes away it is checked for soundness: frost-split faces, soft cores and sulphate-damaged edges go to the skip, while good bricks are cleaned of old mortar and set aside. Reusing sound original brick keeps the match with the rest of the house, which matters more than people expect on a stack seen from the street.

How far down it goes is decided as the work progresses, not just from the ground. The aim is to reach sound masonry with a solid bed beneath it, which may be a few courses or the full height above the roof. A stack that has leant or cracked sometimes proves sound a short way down, and sometimes does not. We would rather find that out as the courses come off than guess at the quotation stage, so the written quotation sets out the likely depth and what changes if the brickwork below proves worse.

Pots come down early and are kept if they are good. Cowls and guards likewise. If the flue is in use, work is planned to keep debris out of it, and flue matters remain with a HETAS or Gas Safe registered installer or a sweep.

Setting out, bond and bricks

Before the first new course goes on, the stack is set out. That means finding true vertical and level lines from the house, and fixing the position of the corners so the new work lines up with what remains below. Taking time here is what makes the finished stack look straight from the pavement, and a stack built a few millimetres out at the base is visibly out at the top.

Bond is the pattern the bricks are laid in so that the vertical joints in one course do not line up with those in the next. A good bond ties the stack into a single mass, with no through-line along which a crack can run. Old stacks often use a pattern matched to the house, and we follow it where the originals allow. Each course is checked with a level and a plumb line as it goes up.

The mortar is chosen for the job, with a mix suited to a stack that is exposed on every face, as described in Repointing a Chimney: Why the Mortar Mix Matters More Than the Finish. Bricks are wetted or not according to their absorption on the day, and joints are tooled to shed water rather than hold it. Bedding is generous, because a starved joint is a weak one.

Lead, head and finishing

With the shaft up to height, attention moves to the places where water gets in. A damp-proof tray goes where the stack passes through the roof, as covered in our separate guide on trays and cloaks. The lead then follows: apron, soakers, stepped flashings and back gutter, chased into sound mortar and dressed to shed water, as set out in Lead Flashing or a Cement Fillet? How to Tell Which You Have.

The head is the top of the stack: a sloping cement flaunching holds the pot, throws water outward and caps the brickwork. It is formed once the pot is bedded at the correct height and the mortar has taken its first set. A capped or vented finish is used instead where the flue is redundant.

At the end the scaffold stays until the lead and flaunching are ready, because a rushed head undoes the work below it. Debris is cleared, gutters checked for dropped mortar and the roof slopes swept. For more on how we work in the area, see the chimney page for chimney repairs in Ellesmere Port.

What you will see and hear

Days one and two are mostly scaffold and protection, which can be noisy and looks like a lot of effort for little visible progress. Taking down comes next and produces dust and the clatter of rubble. Rebuilding is quieter, and the stack visibly rises, which is when most householders relax.

Weather decides the pace. Fresh mortar does not go on in heavy rain or hard frost, so a wet week can add days, and we will keep you told rather than hurry. Please keep windows closed and washing off the line on work days, and keep children and pets away from the working area below.

Our work is on the outside of the chimney only. We rebuild stacks, but we do not do fireplace or internal work, and the quotation, which is free and in writing, spells out the extent of what is included so there are no surprises.