At the very top of a chimney stack sits a detail that most people never think about until it cracks: the flaunching, a fillet of mortar shaped around the base of the pots to hold them firmly in place and shed rainwater away from the flue openings. It's a small amount of material doing an outsized job, and when it fails, the consequences show up well beyond just the top of the stack.
Flaunching is exposed to more extreme weathering than almost any other part of the chimney, sitting fully open to sun, frost and driving rain with no roof covering to shelter it. Over years, this exposure causes it to crack, and once cracks appear, rainwater collects in them rather than running off, accelerating the damage through repeated freeze-thaw cycles until sections start to break away entirely.
Once flaunching has failed, water can track down between the pot and the surrounding brickwork, finding its way into the flue itself or seeping into the stack's core, sometimes reappearing as a damp patch well below the roofline. On the taller period stacks found on some properties in Barton Hill, this can mean water travelling a fair distance internally before it becomes visible as a problem indoors.
Repairing flaunching involves removing the cracked or loose material entirely rather than patching over it, since a partial patch tends to crack again at the join with the old material within a season or two. New flaunching is shaped and finished to shed water properly, with the pots reseated securely, restoring both the weatherproofing and the visual finish at the top of the stack.
Renewing flaunching is also the natural moment to check the pots themselves are sound before reseating them, since there's little point bedding a cracked or badly weathered pot into brand new flaunching only to find it needs replacing again shortly after. Doing both together, where needed, is more efficient than treating them as separate jobs. The mortar mix used for flaunching is typically stronger and less porous than the mix used for repointing the body of the stack, since it sits fully exposed with no brick either side to share the weathering load. Using an unsuitable mix, or simply reusing leftover pointing mortar rather than a proper flaunching mix, is a common reason new flaunching can crack again sooner than it should. Because flaunching failure is so often the root cause of leaks that get blamed on brickwork or flashing further down the stack, it's one of the first details worth ruling in or out whenever a chimney leak is being investigated.
Because flaunching sits at height and its condition isn't always obvious from the ground, it's easy for cracking to go unnoticed until water ingress becomes a bigger issue. If your chimney hasn't had its flaunching checked in a while, we offer free inspections across Barton Hill and can renew it as part of a wider chimney check-up if needed.
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