How often does a chimney need repointing?

Why a calendar is the wrong test

People like a number, and the number most often quoted is that a chimney needs attention every 30 to 50 years. HomeBuilding gives that range for repairs to a chimney in general. It is a useful ballpark and no more than that. Mortar that went in well, in a sheltered position, can outlast the range; mortar that went in badly, on an exposed stack, can fail well before it.

The New Forest National Park Authority makes a related point about old buildings: in many instances, pointing of more than 100 years old is still in perfectly sound condition, and only areas of missing or badly eroded mortar should be repointed. The principle is to repoint what has failed, not to repoint everything because a decade has passed.

Repointing too early causes its own harm. Raking out sound mortar harms the edges of the bricks or stones, and a stack repointed unnecessarily has lost original material for nothing. The aim is to act when the joints need it and not before.

What shortens or lengthens the interval

Exposure comes first. A stack rises clear above the roof and takes wind-driven rain on all four faces, so it ages faster than the walls under it. Stacks on the exposed side of a hill, or on tall houses with nothing sheltering them, wear faster than those tucked behind a gable.

The mortar mix is the second factor. Traditional lime mortar is weaker than the stone or brick beside it, so the joint wears and the masonry survives. Hard cement mortar does the opposite: it is stronger than the units, traps water and sheds the damage onto the stone. A stack repointed in cement can need work sooner than an old lime-pointed one, and it can damage the stone as it fails.

Workmanship matters just as much. Joints that are not raked out deeply enough, mortar that is applied too wet or left to dry too fast in the sun, and pointing that is smeared over the face of the masonry all fail early. The flue also plays a part, since acidic condensation from some fuels attacks the mortar from inside.

Brick stacks and stone stacks

On brick, the pointing is the weak point and the bricks themselves are usually the more durable. A sound brick stack with eroded joints is a good candidate for repointing in a mortar matched to the age and type of the brick. Lime-based mixes are widely used on older brickwork because they allow the wall to dry.

Stone behaves differently. A stack of Bath stone, a soft limestone, reacts more strongly to the mortar. Pointing it in lime protects the stone, and pointing it in cement shortens its life. The reasoning is set out in cement on Bath stone, and lime repointing is the method we use, described on our lime repointing page.

The Bath Preservation Trust raised the same issue on a stack at Walcot Buildings, asking for lime pointing so the stonework could breathe and observing that cement could have aggravated the decay. Listed stacks need extra care, so see listed chimneys before any work.

Signs it is due

Much can be judged from the pavement with binoculars, or from an upstairs window. Look at the joints between bricks or stones. Sound pointing is flush or slightly recessed and firm. Failing pointing is recessed deeply, crumbling, cracked or missing, and the edges of the masonry show.

• Mortar debris. Sandy crumbs on the roof, in the gutter or on the ground below the stack are a sign that the joints are shedding.
• Open joints. If you can see daylight or a dark gap between units, water can get in.
• Damp inside. Staining on the chimney breast after rain often traces back to the stack above, as we explain in why a chimney leaks.
• Plant growth. A buddleia or ferns growing from the stack means the joints have opened and held soil.
• A lean or a crack. Open joints that run in a line, or a stack out of plumb, need a closer look at the structure; see leaning chimney.

A flat patch of missing mortar is a small repair. Widespread failure on all four faces points to a full repoint.

How often to look

Look at the stack from the ground once a year, ideally in late autumn before the worst of the weather, and again after a hard storm or a hard frost. Frost matters because water in open joints freezes and expands, which splits the mortar and the faces of soft units.

Ask for a close inspection every few years, or sooner if something looks wrong. A roofer on a ladder or a scaffold sees things from the ground you cannot: hairline cracks, hollow-sounding mortar, a loose pot, a lifted flashing. We survey free of charge and photograph the stack, so you can see for yourself what condition it is in.

Do not wait for a leak. A stack that has stained the ceiling has been taking in water for some time, and the damp may have reached timbers and plaster by then. Keeping the pointing up costs less than repairing what water does after it gets in. More on stack work is in chimney repairs. A policy will not usually pay for it either, as chimney repair insurance explains, because gradual wear is maintenance.

What repointing involves and what it costs

Repointing means raking out the old mortar to a depth that suits the joint, brushing out the dust, wetting the masonry and filling the joints with fresh mortar, which is then finished to suit the style of the original. It is done by hand, a few joints at a time, and it needs a good working platform. On a tall stack, that means scaffold, and scaffold is often a big part of the bill.

MyBuilder's chimney repair cost guide (2026) gives typical UK ranges: repair £500 to £2,000, with repointing averaging about £750. It adds that a simple patch costs about £250 without scaffold and £550 to £650 with it. These are typical ranges and not Empire prices, and stack height, stone or brick and lime work all move the figure. Your fixed quote follows the survey.

If repointing reveals loose or spalled masonry, a partial rebuild may be the better repair, and the survey, with photographs, will show it. Repair is the aim where it works.