How Often Should a Chimney Be Repointed?

Why there is no set number of years

Ask a dozen people and you will hear a dozen answers, usually between twenty and fifty years, and none of them is wrong in every case. The reason is that a chimney stack is among the most exposed parts of a house. It stands clear of the roof with all four faces in the weather, takes rain from every direction, freezes first and dries last. How fast the mortar wears depends on what it is made of, how well it was laid, how exposed the stack is, and what is passing up the flue.

A stack in a sheltered street, built with a good lime mortar and kept dry by sound flashings and flaunching, may go for generations before it needs attention. A tall stack on a hillside estate, built with a weak or very sandy mix and fed with condensation from a boiler flue, can be worn back in a fraction of that time. The calendar is a poor guide. The condition of the joints is a better one.

What affects how quickly mortar wears

• Mortar type: lime mortar is softer and more forgiving, while hard cement mortar can crack and trap water if used on soft old brick.
• Exposure: stacks on high ground or on the south-west side of a house meet the worst of the wind-driven rain.
• Flue use: gas boilers and some fuels produce acidic condensation that attacks the inside of the stack and the joints from within.
• Water management: failed flaunching or flashings let water in and speed up damage far beyond what rain on the face of the bricks would do.
• Frost: water in a joint freezes and expands, breaking the mortar into grit season by season.
• Previous repairs: a patch of hard mortar over soft brick tends to damage the bricks around it.

Signs it is time to repoint

You do not need a ladder to look. From the garden or the street, with binoculars if you have them, the signs are easy to read. Joints that are recessed deep into the brick, with a shadow line, show that mortar has eroded. Mortar that is powdery or sandy when it falls, or grit in the gutter below, is another sign. Bricks that look loose or sit out of line, and gaps wide enough to see daylight through, call for attention soon. Damp on the chimney breast inside the house, vegetation growing on the stack, or staining down the brickwork can all be related. Our guide to signs of chimney damage lists these in more detail.

If the stack leans, shows diagonal cracks or has bricks missing, repointing may not be enough, and the situation is more urgent. That is the territory of leaning chimney stacks, and it is better to act sooner than later.

A sensible routine

For most houses a simple pattern works. Look at the stack from the ground in spring and autumn, and after any severe storm. Have it checked properly by a roofer every few years, or when you have other roof work done and the access is up. At each inspection, ask for photographs of all four faces, the flaunching, the pots and the flashings, so you can compare from visit to visit and see the rate of change. If the mortar has worn back beyond about the depth of a fingernail, or you can easily scrape it away with a key, plan repointing within the next year or so. If it is firm and flush, leave it alone. Repointing sound mortar for the sake of it removes good material and adds cost, and we say so when we find a stack that does not need work.

It is also worth keeping records. Note the date of any repair, the mortar type used and who did it. When the stack is next inspected, that history tells you what you are dealing with, and an insurer will prefer to see it, as our page on whether insurance covers chimney repairs explains.

What repointing costs and how it compares with leaving it

UK cost guides give chimney repointing as £450 to £1,200, with about £750 as a typical job, although the final figure depends on the height, the access and the amount of mortar to replace. Repointing is cheap compared with rebuilding. Leaving worn joints for years lets water in, loosens bricks and can turn a repoint into a partial rebuild, which costs several times more. Your fixed quote follows the survey. Pick the right mortar for your stack as well, and see lime or cement mortar for chimneys for how to choose. For the whole range of work, go to chimney repairs in Basingstoke.