Chimney flaunching: repair and replacement

On top of a chimney stack sits a flat or domed slab of masonry, the crown, or in older stacks simply the top courses of brick. Pots stand on it. Flaunching is the sloping bed of mortar that fills the gap between each pot and the edge of the stack, and it is shaped so that its surface falls away from the pot in every direction.

Three things depend on it:

• Holding the pot. The bed grips the base of the pot and keeps it upright in wind. A pot set in sound flaunching is a stable thing. One standing in a cracked, crumbling bed is loose, and a gale can lift it clean away.
• Shedding rain. The slope sends water outward and off the stack, so rain does not collect at the pot or run into the flue.
• Sealing the top of the stack. Flaunching closes the junction between pot and brick, which would otherwise be an open gap into the brickwork below.

It is not the same as pointing. Pointing is the mortar in the joints between bricks, down the face of the stack. Flaunching is the cap-level bed at the top, which carries the load of the pot. Our chimney repointing guide covers the joints; this one covers the crown.

Where a stack carries a cowl or a cap, those fittings also depend on the flaunching for their footing. Our chimney pots, caps and cowls guide explains the options.

Mortar is hard, but it is not indestructible, and the top of a chimney is a punishing place for it. Several things happen together.

Water gets into hairline cracks

The first sign of trouble is usually a fine crack, often between the flaunching and the pot or along the edge where it meets the brick. Rain enters, the mortar absorbs it and cold weather turns the trapped water to ice that widens the gap. Each cycle makes the crack a little worse, and over time a piece of bed breaks away.

The mortar was too weak, or too strong

A bed that is mixed poorly or laid thin can dust away on the surface. One that is much harder than the brick beneath can crack at the junction, because the two materials move differently. This is one reason older stacks are repaired with a mix chosen to suit them, a point our answer on lime mortar for old chimneys takes up.

Stacks that move

A stack that leans or has opened at the joints will pull the bed apart. If you see flaunching failing again and again, the cause may sit lower down, in the pointing or the brickwork, and renewing the bed alone will not hold.

Wind loading

Pots act like sails, and the exposed positions along the Sussex coast give the wind a clear run at them. A bed that has already cracked is easily worked loose by repeated gusting, and the pot starts to rock.

Flaunching often fails in a hidden way. The crack lets in water, the water works downward and the first symptom is a damp patch in a bedroom or loft rather than anything visible on the stack. Our answer on water around the chimney in the loft shows how to read that.

You can check a good deal from the ground, on a dry day, with binoculars. Pick out the top of the stack against the sky and look for these:

• Cracks running through the bed or round the base of a pot, especially wide ones you can see from the street.
• Missing chunks where a piece of mortar has dropped away and exposed the brick or the pot underneath.
• A leaning or rocking pot. If the pot sits at an angle, or moves in strong wind, the bed has lost its grip.
• Moss, grass or small plants growing on top. Seeds only take where mortar has broken and holds moisture.
• Mortar debris in the gutter, on the flat roof below or on the ground by the house wall.

Inside the house, signs are indirect. A patch of damp on the room side of the stack, wallpaper lifting beside the fireplace or a musty smell in the room points to water entering somewhere along the stack, and the crown is a prime suspect.

What not to do

Do not go up and smear mortar or sealant over cracks yourself. A wet patch coat sits on top of the old bed and falls away in the first frost, and climbing a stack without the right access is how people get hurt. Treat a loose pot as a hazard: it can drop onto a path or a neighbour's garden, so keep people away from the area below and arrange a safe repair.

If a gale has already taken a pot, the steps in our chimney storm damage guide cover what to do first, and a pot that has cracked as well as come loose is normally renewed rather than re-bedded.

Small cracks are sometimes dealt with by raking out and filling, but a bed that has lost its grip on the pot almost always means starting again. A proper job runs in order:

1. Access. A safe working position at the top of the stack comes first. On a house of any height that normally means scaffolding, or a tower that reaches the chimney.
2. Taking off the old bed. The loose flaunching is chipped away, and the pots are lifted clear if they need to be reset or replaced. Any broken pot goes.
3. Checking what is underneath. With the bed off, the top courses of brick can be inspected. Loose or cracked brickwork is rebuilt before anything goes back, otherwise the new bed sits on a poor base.
4. Resetting the pots. Each pot is bedded plumb and level in fresh mortar, with the flue left clear.
5. Forming the new flaunching. The mortar is trowelled to a smooth, sloping profile so water falls away from the pot and off the stack. It is finished tight around the base with no gap.
6. Tidying. Old mortar is cleared from the roof and gutters, and the site is left clean.

With a roofer already at the top of the stack, the pointing and the lead flashings deserve a look too. A job that renews the crown but leaves failing joints below it only moves the leak. Our chimney flashing guide covers the junction at roof level.

We photograph the top of the stack during the survey, so you can see the cracks and the condition of the pots for yourself. You then get a verdict on the crown, with reasons: re-bed, patch for now, or rebuild. If re-bedding the pots will hold, that is all we advise, and a new stack is the answer only when the brickwork has gone.

The mortar is cheap. Getting to it is not. The national cost guides carry no separate price for flaunching, which is rarely a job on its own; it is usually done with the pots, the pointing or the flashings, and priced as part of the stack. What they do list is the cost of reaching the top.

In the scaffolding costs Checkatrade published in October 2026, a chimney scaffold comes to around £660 a week. A low bungalow stack within reach of a roof ladder or a tower brings a smaller access bill. For a three-storey terrace over a pavement, the scaffold can cost more than the repair itself. Scaffolding over the pavement falls under section 169 of the Highways Act 1980, so a licence from the highway authority is needed; in West Sussex that means at least 10 working days' notice and £266 for a month.

For chimney work as a whole, the MyJobQuote guide updated on 22 September 2026 prices full replacement of chimney lead at £350 to £460 without scaffolding and £700 to £920 with it. That jump shows how heavily the scaffold weighs on any chimney job, flaunching included.

Three things push the price of a flaunching job up or down:

• the height and position of the stack, and so the access it needs;
• the number of pots, and whether any have to be replaced;
• what the survey finds underneath, such as loose brickwork at the crown.

A price for a single pot on a bungalow and one for a six-pot Victorian stack are very different numbers. Our quote is written, arrives once we have been up to look, and states a single total that we consider good value and fair. For the wider picture, see what chimney repairs cost.

Not every stack should be treated the same. Several situations call for more care.

Old brickwork and soft mortar

Victorian and earlier stacks were laid in softer mortars, and a hard modern mix on top can trap moisture and damage the bricks beneath. The mortar for a repair should suit what is already there. If your stack is old, ask what mix is proposed and why, and whether pointing needs doing at the same time.

Conservation areas and listed buildings

Renewing flaunching like for like, in the same form, is repair work, and does not usually raise a planning question. A different pot, a changed height or a rebuilt stack is different, and on a listed building or in a conservation area with an Article 4 direction it may need consent. Our guide to chimneys in conservation areas and on listed buildings explains where the line falls.

Exposed coastal stacks

Chimneys close to the sea take driving rain and strong gusts, and the crown takes the worst of it. We cannot give you a rating for any particular road, but the sensible response is the same everywhere along this coast: check the top of the stack before the autumn gales and again after a bad blow, and fix a cracked bed while it is a small job.

Unused chimneys

A stack over a disused fireplace still needs a sound crown. If the flue has been capped or vented, the capping depends on a sound bed. Do not let an unused stack drift, because the bed keeps weathering whether or not a fire is lit below.

A last point: flaunching is a small repair that prevents a large one. A cracked bed caught early costs far less than the damp, repointing and brick repair that follow when water has been entering for years.