A brick stack stands in the harshest spot on the house. It is surrounded by air on all sides, it takes rain, wind and frost from every direction, and it has hot gases passing up the middle. Mortar joints crumble, brick faces flake away and, in time, the whole top of the stack can loosen. Most of this is repairable, and the repair is usually modest if it is caught early. What decides the outcome is the method: which bricks are replaced and which are left, what the new mortar is made of, and whether the cause of the damage is dealt with as well as the damage itself. This guide describes the common faults on brick stacks, how each one is repaired, the points on matching and mortar that make a repair last, and the typical cost figures reported for chimney work in the UK. For the wider service, see our chimney repairs page.
How a brick stack breaks down
Brick is a tough material, but a chimney asks more of it than almost any other wall on the house. Four forces do most of the damage.
Water and frost
Bricks absorb some moisture. When that water freezes it expands, and the surface layer of the brick can break away. Stacks get wet from rain on every face, and nothing on a chimney dries them as quickly as a wall inside a warm building. That makes the stack more likely to suffer from frost than the rest of the house.
The flue itself
Smoke and flue gases are acidic and contain moisture. In a flue with a failing or missing lining, those gases can attack the mortar and the inner face of the brick. The effect can be a stack that bulges or leans slightly to one side as the joints on the inside expand. A leaning stack is serious, and our page on the leaning chimney explains when it needs urgent attention.
Hard repairs
An earlier repair in cement mortar can be harder than the brick around it. Water then leaves through the brick face, not through the joint, and the face spalls. This is a very common reason for a stack to look worse after a repair than before.
Failed details above
Cracked flaunching (the mortar crown that slopes down from the pots), failed lead flashings and missing pots all let water into the brickwork. Fixing the brick without fixing the detail that is letting the water in is a waste of money.
Looking at a stack from the ground, you may see none of this. Binoculars help, and a camera with a zoom helps more. Look for missing mortar, bricks with their faces gone, green growth, white salt deposits and any lean. Anything more than a few loose bricks is worth having looked at from the roof.
Spalled bricks: what they are and what can be done
Spalling is the loss of the outer face of a brick. It leaves a rough, pitted surface and exposes softer material beneath. It can affect a single brick or a whole band of them. A spalled brick is not always a failed one. If the loss is shallow and the brick is still sound behind, it may do its job for years, though the exposed core weathers faster than the fired face.
There are three ways to deal with a spalled brick, and the best one follows the depth of the damage.
- Leave it. Where the spalling is slight, the brick is firm and the surrounding joints are sound, there may be nothing to do. Monitor it at the next inspection.
- Turn it. A brick sometimes has a good face on the other end. It can be carefully removed and set back with the sound face outward. This only works for bricks in a position where both ends are accessible, and it suits stretchers in a wall that is not too deep.
- Cut out and replace it. Where a brick has crumbled or lost enough of its face to let water in, it is cut out and a matching brick is set in its place, bedded in new mortar.
Cutting out a brick must be done without disturbing the ones around it. The old mortar is removed with care, because levering at a brick can shatter its neighbours. The new brick goes in with a full bed of mortar on every side and is pointed to match the joints around it.
If many bricks on the same face are spalling, there is usually a cause that a single replacement will not cure, such as persistent damp, a cement repair or a failed flashing. Treat the cause first. When damage runs deeper than the faces of a few bricks, read about a cracked chimney stack.
Failed pointing and how it is repaired
Pointing is the visible finish to the mortar joints. When it erodes, the joints become hollow, water gets into the wall, and the bricks begin to move. Failed pointing is the most common fault on a brick stack, and the repair is repointing: the old mortar is raked out to a set depth and new mortar is packed in.
Depth matters. Joints are cut out far enough to give the new mortar a good grip, and no deeper than the wall allows. Cutting too deep weakens the wall, and cutting too shallow gives mortar that falls out again. The work is done with care to leave the bricks undamaged. Power tools can chip brick edges, so on older stacks hand tools are often safer.
The mortar is the key choice. A mortar that is stronger and denser than the brick pushes moisture into the brick, and the brick then spalls. For most older brickwork the right mortar is a lime-based one, which is softer than the bricks and lets the wall dry through the joints. The reasoning is set out under lime repointing. Modern brick in good condition tolerates a stronger mix, yet one rule holds throughout. Let the joint be the sacrificial part, since joints cost less to renew than bricks.
Colour and finish are the other half. Mortar is matched to the existing joints in tone and in how the surface is finished, such as flush, slightly recessed or tooled. A raised ribbon of cement pointing is a different story: it sheds water onto the brick faces and traps it behind the ribbon.
How often a stack needs repointing is a question of condition, not the calendar. One source on chimneys suggests a stack may need repair every 30 to 50 years, while a national park authority notes that old lime pointing over a century old can still be sound. Only the areas that have failed need to be redone. We look at how often in our page on how often to repoint a chimney.
Replacement bricks and matching
When bricks have to be replaced, the new ones should be as similar as possible to the old in size, colour, texture and strength. A mismatch is visible for as long as the stack stands, and a brick that is harder or softer than its neighbours will wear differently.
There are three sources of replacement brick.
Reclaimed bricks
Salvaged bricks from demolished buildings are often the best match for an old stack, because they carry the same weathering, size and texture. They need sorting, since some are too damaged to reuse, and supply of a particular colour can be limited.
New bricks made to match
Specialist makers produce bricks in traditional sizes and colours, including hand-made and stock types. A new brick can be a close match, though it looks fresher for the first years.
Bricks from within the stack
On a stack that is being partly rebuilt, sound bricks taken from the top courses can be reused lower down, with new or reclaimed units used in the less visible spots.
Bonding matters as much as colour. A replacement brick must follow the pattern of the courses around it, such as English or Flemish bond, and must sit at the same level so the lines of the joints continue. When whole courses at the top are rebuilt, the new brickwork is laid in lime or another suitable mortar and tied in so that it acts with the old work below.
Where only a few bricks are in doubt, a small patch is often all that is needed. Where the top of the stack has lost bricks in several places, the work turns into a part-rebuild, and a good survey will say where one stops and the other starts. Our guide to capping a chimney is useful if the flue is unused, as a vented cap protects the freshly repaired top.
Flaunching, flashings and the parts that protect the brick
A brick repair that ignores the parts above and below it will not last. Two details matter most.
The flaunching and pots
Flaunching carries rain away from the crown of the stack. If it has cracked or pulled away from the pot, water runs straight into the brickwork below. Renewing it is a small task if done with the brickwork, and an expensive one if done later from a new scaffold. It should be shaped to slope outward and finished so it cannot hold a pool of water. Our page on chimney flaunching covers it in detail.
Lead flashings
At the point where stack and roof meet, a lead flashing closes the gap. Soakers beneath it, tabs of lead tucked into the tile or slate courses, guide water out onto the slope. If the lead has lifted, split or been displaced, water gets into the junction and soaks into the lower bricks and the roof timbers. Lead done properly is among the longest-lived parts of a roof, but it is only as good as its fixings and the mortar it is tucked into. Our page on chimney flashing lifespan explains how long to expect and when to renew.
Sometimes owners are tempted to seal the brickwork with a clear waterproof coating. For most old brick stacks this is not advisable, since a coating can trap moisture that is already in the wall, and it is hard to reverse. Repairing the joints and the details is a more reliable answer. We discuss options in our page on chimney waterproofing.
Doing the brickwork, flaunching and lead in one visit makes sense, because the access for one is the access for all. Several short visits to the same stack each pay for scaffold again.
When to repair and when to rebuild
Repair suits a stack that is structurally sound: upright, with firm brickwork and flaws confined to joints and a handful of bricks. Rebuild is for a stack that has failed through its depth. The usual signs that repair will not do are:
- a visible lean, or a step in the line of the courses
- cracks that run through bricks and joints together
- bricks that move when touched
- joints that have lost mortar to a great depth, on several faces
- an inner flue that is breaking up and shedding debris
A partial rebuild takes down the top courses to sound brickwork and builds them again, re-using the good bricks and replacing the poor ones. A full rebuild takes the stack down to the roof line or lower. In both cases the pots, flaunching and lead are renewed along with the brick. Our page on chimney rebuilds sets out the sequence.
Because chimneys are high and awkward, getting this decision wrong is costly. Repairing a stack that should have been rebuilt means paying twice. Rebuilding a stack that only needed repointing wastes money and loses sound original brickwork. A survey from the roof, with photographs of each face, is how we decide. We recommend repair where repair works, and we say clearly when it does not.
Neighbours matter too. On terraces and semis a stack is often shared, and work on one side affects the other. How that is handled is covered where we discuss a party stack serving two houses.
What brick chimney work typically costs
Figures published by third-party cost guides give a sense of scale. They describe the market nationally, not what Empire charges, and cannot replace a survey. MyBuilder's 2026 chimney repair guide reports typical repair work of £500 up to £2,000, repointing around £750 on average, flashing work up to £1,200 at the top end, and rebuilds that begin near £2,000 and can pass £10,000. The same guide puts a simple patch at about £250 with no scaffold, rising once scaffold is added.
The things that move a brick chimney quote are fairly predictable:
- the height of the stack and how far it rises above the roof
- how much of it needs work, from a few bricks to several faces
- the type of mortar, with lime work taking longer than a modern mix
- whether the bricks can be matched from stock or have to be sourced
- scaffold, which can be the single largest item
- the lead and flaunching if these are renewed with the brickwork
Our page on chimney repair cost goes through those drivers in more detail.
Once we have been up on the roof, you get a fixed written price, with the scope itemised: which bricks, which mortar, whether lead and flaunching are included and what scaffold is needed. Rubbish leaves with us, and the work sits under our written ten-year workmanship guarantee.