The short answer
On an older stack built in soft brick, yes: lime mortar is usually the right choice. It is weaker than the brick, so it takes up the movement and the wear instead of the brick face. A hard cement mix is stronger than the brick, traps moisture behind it and can pull the brick faces off. A newer stack in hard modern brick is more forgiving, and the survey should say which you have.
Why the mortar should be softer than the brick it holds, how a roofer judges your stack, and what repointing typically costs.
Why the mortar must be weaker than the brick
Repointing means raking out the crumbling joints between the bricks and filling them with fresh mortar. The key idea is that the mortar is the sacrificial part. Weather, frost and the slow swelling and shrinking of a stack in sun and rain all push on the joints, and something has to give. If the mortar is softer than the brick, the mortar gives, and replacing a joint is a small job.
Lime mortar is made to behave that way. It is slightly flexible, and it is open enough to let damp leave the wall by evaporating through the joint. Cement mortar is dense and rigid. On a chimney, which is the most exposed masonry on the house, the stack soaks up rain from every side, and a hard cement joint blocks the way out. The water then escapes through the face of the brick instead, carrying salts with it and freezing in winter, so the surface flakes away in layers. Our answer on spalling chimney bricks covers what that looks like.
Once the joints are hard and the bricks are soft, the damage tends to be on the bricks, which are far harder to replace than a line of mortar.
Is your stack old enough to need lime?
Age is a guide, but the brick tells the story. Older stacks are often built in soft, low-fired brick, and those should be pointed in a lime-based mix. Stacks from the post-war estates may be in harder machine-made brick, and a roofer may decide a gauged modern mortar suits them better. There is no rule you can check from the pavement, so ask what the roofer sees in the brick and the joints, not just which bag they prefer.
A few clues can be read from the ground with binoculars. Crumbling, sandy mortar that falls away when scratched is usually an old lime joint that has simply run out of life. Sharp, grey, ridged cement that stands proud of eroded brick edges is the warning sign of an earlier cement repair doing harm. If previous repointing has used cement on soft brick, the roofer has a choice to make about how much to rake out, and should show you close-up photos before agreeing the work.
On a listed house, or in a conservation area, the council may take an interest in the mortar too, so put the question to its planning team before any scaffold goes up.
Raking out, filling and curing
Good repointing starts by raking the old joints out to a sound depth, usually about twice the joint width, and brushing out the dust. Shallow scraping and smearing new mortar over the top will not hold. The joints are then wetted, filled in layers and finished flush, or slightly recessed, so rain runs off instead of pooling on a ledge. Lime sets more slowly than cement, so it needs shelter from hard frost and heavy rain while it cures, which is one reason winter repointing needs thought and a dry spell is the best time to book.
Because the stack is up in the weather, the crown, the flaunching around the pots and the flashing at the roofline should be checked while the access is up. Repointing a stack with a cracked cap is only half a job.
Ask your roofer to explain the mix in plain words, since lime mixes vary with the brick and how exposed the stack is. A well-judged lime repoint is a long-lasting repair, but no mortar is permanent, and the joints will need looking at again in due course. Our guide to chimney repointing sets out the whole job.
What lime repointing costs
As a national guide, Checkatrade's October 2026 chimney repointing table gives an average of around £750. The low end, near £300, is a short stack on a low roof, while a mid-terrace stack at the ridge, where scaffold is needed, reaches about £1,000. Its April 2026 chimney repairs table puts repointing at £300 to £1,000. Treat these as a yardstick only, since the figure for your stack depends on its height, how much mortar has failed and the access.
Scaffold is the biggest swing. A stack at the ridge cannot be worked on safely from a ladder alone, and the scaffold can cost as much as the masonry. Our answer on scaffolding for chimney repair sets out when it is needed. Check that VAT and the scaffold sit inside whatever figure you are given.
Lime itself costs little more than cement. What you pay for is time: raking out properly, working in small areas and aftercare. Once we have surveyed the stack you receive a single written price, covering the whole repoint. For the wider picture of stack work, see our chimney repairs hub. Send us a photo of the worst joints and the height of the stack, and we will say what the first check will be.
More on this in Chimney Repairs in Crawley
Two lime mortar worries
Can lime be laid over old cement pointing?
Not as a lasting fix. New lime pressed over hard cement has nothing sound to grip, and the cement keeps blocking moisture underneath. The cement has to be raked out first, taking care not to chip the brick edges. How far to go depends on the brick, which is why a close look comes before any price.
Is lime pointing weaker than cement and so less safe?
It is softer by design, and that is the point. The stack is held up by the brickwork, not by a rock-hard joint. A softer joint protects the brick and can be redone without damaging it. If a stack is leaning or the brick itself has failed, repointing is not the answer and a rebuild may be.