Flaunching, pots and pointing — keeping your chimney weathertight

Most chimney problems we see are problems with the same three parts: the flaunching, the pots, and the pointing. Each does a specific job. When any of them fails, water gets in. Here’s what each does and how to spot trouble.

The flaunching

What it is: the angled bed of mortar at the very top of the chimney, surrounding the chimney pots. Usually about 50-75mm thick at the pot, sloping down to about 25-30mm at the edge of the stack.

What it does: sheds rainwater away from the pot and the top of the flue. Without it, water would pool around the pot, run down inside the flue, and saturate the brickwork.

What goes wrong: cracking, splitting, lifting away from the pot or the stack. Caused by:

• Weather — frost particularly, water getting into the mortar, freezing, expanding
• Age — mortar has a finite life, typically 30-50 years on a chimney
• Building movement — slight settlement shifts the mortar and cracks it

The fix: strip out the old flaunching, re-bed the pots if needed, lay a fresh bed of mortar with the right slope, finish with a weathering detail at the edge. Half a day to a day’s work.

The chimney pots

What they are: the clay or terracotta tubes sitting on top of the chimney stack, one per flue. Visible from the ground as the cylindrical bits on top of the chimney.

What they do: cap the flue, prevent rain and debris falling down, and (with a working fireplace) carry the fumes safely away.

What goes wrong:

• Cracking — usually frost damage or impact (a bird’s nest dislodged, a ladder leaned against them, etc.)
• Wobbling — the pot has come loose from the mortar bed. Usually means the flaunching has failed.
• Dislodging — the pot has fallen off entirely. The flue is now open to the weather.
• Old salt-glaze pots — older Victorian and Edwardian chimneys sometimes have particularly fine salt-glazed pots that crack more cleanly than newer ones.

The fix:

• Single cracked pot: usually a like-for-like replacement if the existing style is available
• Multiple cracked pots: usually replaced as part of a chimney overhaul
• Wobbly pot: lifted off, cleaned, re-bedded in fresh mortar on a renewed flaunching

If the chimney has been used for a real fireplace and you want to keep it in use, the flue also needs to be in good condition. We can do a CCTV inspection if needed to check.

The pointing

What it is: the mortar between the bricks of the chimney stack itself. Same as the pointing on the rest of the house, but takes more weather because it’s up high.

What it does: keeps the bricks solid and weatherproof. Without pointing, water gets into the joints between bricks and freezes, which spalls the brick faces off.

What goes wrong:

• Recessed pointing — the mortar has worn back from the face of the brick. Usually age-related.
• Missing pointing — mortar has fallen out of the joints entirely. Water’s getting in.
• Spalled bricks — the face of the brick has come off, usually because of water damage. The brick itself is failing, not just the pointing.

The fix:

• Repointing: rake out the old mortar to a depth of about 25mm, repoint with a lime mortar (NOT cement — cement pointing on old brick chimneys causes more problems than it solves, trapping moisture inside the bricks), finish flush or slightly recessed depending on the age of the chimney.
• Spalled bricks: usually means cutting out the damaged bricks and replacing them. Worth doing before the damage spreads.
• Full stack rebuild: when more than about 30% of the brickwork is failing. Last resort before taking the chimney down.

Why chimney mortar should be lime, not cement

This is a specific thing worth knowing. Most chimneys on Bath properties were built with lime mortar, which is breathable. If you repoint with modern cement mortar (which most general builders default to), you create a problem:

• The bricks want to breathe — let moisture in and out
• Cement mortar doesn’t breathe — it traps moisture inside the bricks
• The trapped moisture freezes in winter and spalls the bricks
• The pointing looks fine while the bricks fail behind it

For an old Bath stone chimney, the right pointing is lime mortar matched to the original mix. Most general builders don’t know this. We do, and we specify lime for pointing on period chimneys.

How often each needs doing

Pointing: every 30-50 years on a typical chimney. Faster on exposed sites.

Flaunching: every 25-40 years. Faster if it’s been done badly.

Pots: they last as long as they last. Old ones can be 100+ years old and still fine. Modern replacements are good but not as thick-walled as the originals.

Putting it all together

A chimney that’s overdue on pointing is usually overdue on flaunching too. The cheapest option is usually to do all three at once while the scaffolding’s up. We can book a survey and write up what needs doing in priority order — sometimes the answer is “do the flaunching now, point next year, pots can wait.”