How is a chimney repointed?

Repointing looks simple but the detail matters: how deep the old mortar is cut out, which mix replaces it, and how it cures all decide whether the repair lasts.

The repointing process, step by step

Repointing follows a clear sequence, and each step affects the result. First, safe access is set up — usually scaffolding for a full stack, so the mason can work all round it. Next, the old perished mortar is raked out to a sound depth (typically a couple of times the joint width) using hand tools or a careful mechanical method, without chipping the brick edges. The joints are then brushed clean and dampened so the dry masonry does not suck moisture out of the new mortar too fast. Fresh mortar of the correct mix is pressed firmly into the joints in layers, then the joint is finished (struck) to the right profile to shed water. Finally it is left to cure slowly, protected from rain and frost. The table summarises the stages.

Typical repointing sequence. Method and mortar are adapted to the building's age and materials.

Choosing the right mortar

The mortar mix is the most important technical decision in repointing. On many modern brick stacks, a cement-based mortar is appropriate and durable. But on older, solid-wall and listed buildings, the correct material is usually lime mortar. Lime is softer and breathable: it lets the wall release moisture and flexes slightly with the building, whereas a hard cement mortar on a wall designed for lime can trap water, force moisture into the bricks, and cause frost and salt damage to the masonry faces. Matching the new mortar's colour, texture and strength to the original also matters on older or visible work. This is why a competent contractor asks about the age and construction of your home before quoting, and why "what mortar will you use?" is one of the most useful questions you can ask — the wrong choice can do more harm than the failed joints it replaces.

Why technique and curing decide longevity

Repointing that fails early usually fails because of technique, not bad luck. If the old mortar is raked out too shallow, the new mortar has nothing to key into and soon falls out. If the joints are not dampened, the dry masonry pulls water from the mix and weakens it. If the mortar is not pressed in fully, voids let water sit and freeze. And if it is not cured slowly and protected, it can dry too fast, crack, or be washed out by rain before it has set — which is why timing the work for settled weather and protecting fresh work matters. Lime mortar in particular needs patience: it cures more slowly and must be kept off frost while it gains strength. Good repointing is therefore as much about preparation and aftercare as about the few minutes of pressing mortar into a joint. When all the steps are done properly, the result protects the stack for decades.

When repointing is the right repair

Repointing is the correct repair when the mortar joints have failed but the bricks and the stack itself are sound — they are upright, not cracked, and the brick faces have not perished. In that situation, renewing the joints restores the stack's ability to shed water and prevents the decay from spreading. Repointing is not the answer if the bricks themselves have spalled or crumbled, if the stack is leaning, or if there is structural cracking — at that point a partial or full rebuild is needed, because new mortar around failing bricks will not make the stack safe or durable. A good contractor will tell you honestly which category your chimney is in, ideally after an inspection from the scaffold, rather than repointing a stack that really needs rebuilding. Catching joint failure early, while the bricks are still sound, is what keeps the cheaper repointing option open.

It is also worth knowing how to recognise good repointing once it is done, so you can judge the work and not just the price. Well-finished joints are fully filled and firmly compacted, struck to a consistent profile that sheds water, and matched in colour and texture to the surrounding masonry on visible or older work. Poor repointing shows as smeared mortar across the brick faces, uneven or hollow joints, a hard cement mix on a wall that needed breathable lime, or shallow filling that has not keyed in. Because much of the quality is decided by preparation and curing that you cannot see after the event, it is reasonable to ask the contractor how deep they raked out, what mix they used and why, and how they will protect the fresh work while it cures. A contractor confident in their method will answer readily; vagueness about mortar or technique is a warning worth heeding before the scaffold comes down.

Frequently asked questions

Sources & further reading

• Historic England — repointing brick and stone walls
• Checkatrade — chimney repointing guide
• MyJobQuote — chimney repointing guide

Figures on this page are typical UK ranges drawn from published sources and depend on your specific chimney. They are guidance, not a quotation.