Norwich Roofers rebuilds chimney stacks for homeowners in Brundall, using the right materials for each job rather than a one-size-fits-all approach.
A chimney rebuild is only as good as the materials that go into it. Get the specification wrong and you can end up with a stack that looks sound but fails again within a few years. The key decisions are the type of brick, the mortar mix, the flaunching compound, the type of pot or cap, and the flashing material at the base. This page runs through the main options honestly, including where each one has drawbacks.
The most visible part of a rebuild is the brickwork itself. For a stack to look right and, on older properties, to satisfy planning requirements, the new bricks need to match the existing ones as closely as possible in colour, texture and size. This is more involved than it sounds. Modern machine-made commons are noticeably flatter and more uniform, and they stand out against weathered originals.
For a chimney that is visible from the street or on a property with any heritage sensitivity, it is worth spending more on reclaimed or specialist facing bricks. Reclaimed bricks from a salvage yard can be an excellent match for older stacks, but they need to be frost-resistant and of adequate strength. Not all reclaimed bricks are. A good roofer or brickworker will check the brick specification before using them at height.
For a rear chimney that is largely hidden, or on a modern property, a standard facing brick of the right colour is usually adequate and more economical.
Mortar choice is arguably more important than brick choice. The mortar must be weaker than the brick it bonds, so that any movement stress is absorbed by the joint (which can be repointed) rather than by the brick face (which cannot be repaired once spalled). This is a well-established principle in masonry, but it is frequently ignored when tradespeople use a standard cement-heavy mix because it sets quickly and is easy to work with.
For most chimney rebuilds on traditional brick properties, a mortar in the region of 1 part cement to 1 part lime to 5-6 parts sharp sand is appropriate. The lime keeps the mix slightly flexible and breathable. Omitting lime and using a straight cement-sand mix is faster but harder, and on an older stack it risks spalling the brick faces within ten to fifteen years.
On a listed building or a building in a conservation area, a pure lime mortar (no cement) may be required. Pure lime mortars take longer to cure and require a more experienced hand to use correctly, but they are the right material for historically significant masonry.
The flaunching is the angled mortar bed at the top of the stack that holds the chimney pot in position and sheds rainwater away from the pot collar. Failed flaunching is one of the most common causes of water getting inside a chimney stack. Once the flaunching cracks, water tracks down through the joint and into the courses below.
Traditional flaunching is a cement-sand mix, applied by hand and shaped to shed water. It is functional and durable when properly done, but it can crack if the stack moves at all, and it cannot flex. Polymer-modified flaunching mortars and purpose-made flaunching compounds are now available and offer slightly better flexibility, but they are only as good as the preparation of the surface underneath. If the top course of brickwork is unstable, new flaunching on top of it will not last.
If the pot is cracked or has settled unevenly into the old flaunching, it should be replaced at the same time as the rebuild. Terracotta pots are the traditional choice and remain the most widely available. They come in a range of heights and styles, from plain roll-top designs to taller tapered pots suited to stacks that suffer from downdraught. For a disused chimney, a half-round terracotta cap or a purpose-made ventilating cowl keeps water out while allowing the stack to breathe, which prevents the internal structure from becoming saturated.
Concrete caps are sometimes used and cost less than terracotta, but they are heavier and more prone to cracking over time. For a stack that already needs work, avoid adding unnecessary weight to the upper courses.
The flashing seals the joint between the stack and the roof covering. It is almost always lead on a quality job, and with good reason. Lead is malleable enough to follow the contours of the brickwork and the roof tiles, it lasts for several decades when correctly specified and fitted, and it can be dressed to a neat finish that sheds water reliably.
The flashing typically consists of a stepped flashing up the sides of the stack and an apron at the front. On a wide stack there is also a back gutter behind the stack. The lead is fixed into the mortar joints using wedges and then pointed over. The minimum specification for chimney flashing lead is Code 4 (1.8mm thick), with Code 5 used where there is significant water run-off from a large roof area behind the stack.
Alternatives to lead include aluminium flashing tape and purpose-made self-adhesive flashing products. These are used by some tradespeople as a cheaper or faster option, but they do not last as long as properly dressed lead and they are more prone to lifting at the edges. For a new chimney rebuild, lead flashing is the sensible specification.
Every chimney rebuild we carry out is done from a properly erected scaffold platform. There is no safe or accurate way to rebuild a stack from a ladder, and a good scaffold also protects the roof covering below from falling debris during the takedown. Scaffold hire is a real cost and it should be included in any quote you receive. If a quote looks unusually low, check whether scaffold is included.
When comparing quotes for a chimney rebuild, ask each contractor to specify the brick type and source, the mortar mix ratio, whether the flaunching and pot are included, the lead specification for the flashing, and whether scaffold is included in the price. A quote that does not specify materials is difficult to compare. We cover Brundall and the wider Norwich area. Call us to discuss what your chimney actually needs before committing to any work.
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