Chimney repointing: when and how it's done

From the ground, failed pointing looks like joints that have gone dark and recessed, with bricks standing proud of the mortar. A scatter of sandy grit on the path or in the gutter is another giveaway, because that is what perished mortar breaks down into. Moss and plant growth in the joints, white salt staining and bricks that look loose on one face all point the same way.

Inside the house, the signs show on the chimney breast. Damp patches, flaking paint or staining that comes back after decorating suggest water is working through the stack. Rain that enters through open joints does not run straight down. It soaks into the bricks and moves along them, so the stain may be some distance from the cause.

When it is more than pointing

Pointing is the answer when the bricks are sound. If the faces are crumbling, the stack has moved or the joints have opened on one side, pointing alone will not hold. A stack in that state may need part or all of it taking down, and our guide on when a chimney stack needs rebuilding sets out how that is judged.

Raking out is the removal of old mortar from the joints before new is put in. It is the part nobody sees afterwards, and the part that matters most. New mortar placed over the top of old, loose mortar looks fine for a season and then falls out with the old beneath it.

Old mortar comes out to sound material, generally about twice the width of the joint, which gives the new mortar something to grip and enough thickness to withstand the weather. Hand tools are the safest way to do it on soft old brick, because an angle grinder is quicker but can chew the edges of the bricks and leave the joints wider than they started. On hard modern brick, a careful machine can be reasonable. The brick type decides the method.

After raking out, the joints are brushed clear of dust and dampened, so the new mortar does not dry too fast and weaken. That damping step is easy to skip and often the cause of crumbling pointing that fails within a couple of winters.

Pots, flaunching and flashings are inspected at the same time. If the cap is cracked or the lead is lifting, it is cheaper to deal with them while the access is in place.

The golden rule is that the mortar should be softer and more permeable than the bricks. It is the weaker part and takes the wear. If the mortar is harder than the brick, moisture escapes through the bricks instead, and the faces flake away while the joints stay perfect. That is the reverse of what a chimney needs.

For a house built before the 1920s, with soft bricks, that normally means a lime-based mortar. For a modern stack of hard engineering brick, a sand and cement mix is usual and appropriate. Houses between those eras vary, and the choice depends on the brick. Our page on lime mortar for old chimneys sets out why pre-1920s stacks suit lime and how it is used.

Why not just use cement everywhere

Cement is cheaper, quicker to work and more familiar, which is why it turns up on old stacks that should have had lime. It also sets hard and is far less forgiving of movement. Repointing an old stack in strong cement can move the damage from the joints to the bricks, which is a worse place for it. A leaning stack with sulphate attack in the mortar has a separate set of causes, covered in our guide on leaning chimneys.

The profile of the joint affects both the appearance and the weather resistance. Flush joints, pressed in level with the brick, suit many stacks. A slightly recessed joint can throw a shadow and look right on some older work, but it holds water if recessed too far. Bucket-handle and weather-struck finishes shed water more cleanly.

The colour and texture of the mortar should follow the original. A sample is worked into a hidden area and left to dry, because mortar changes colour as it cures. Matching sand matters as much as the binder: coarse, sharp sand gives a different look from fine builder's sand, and old pointing often has a gritty character that smooth modern mortar does not reproduce.

One finish to avoid is ribbon pointing, where mortar is spread proud of the brick edges in a raised band. It looks tidy for a short while, then cracks along the edges and lets water in behind the bead. Another is smearing mortar across the brick faces, which is difficult to remove and hides the brick pattern.

Reaching a stack is as much a part of the job as the mortar. A low stack on a bungalow can be worked from a ladder. A taller stack on a pitched roof is usually reached with a roof ladder over the tiles, or from a scaffold tower, which gives a firm working platform on all sides.

Scaffold matters because repointing needs both hands, a hawk or pointing tool, and enough time to work each face properly. Rushing a job on a ladder is how joints are missed. MyBuilder's scaffolding guide, updated 21/08/2026, gives high-level chimney scaffold at £400 to £900, and Checkatrade, updated February 2026, gives chimney scaffolding at £660 per week. See whether any quote counts scaffold and VAT within its total. Our answer on whether you need scaffold for a chimney covers when a ladder is enough.

Weather and timing

New mortar needs a few dry, frost-free days to set. Work done just before a hard freeze can be damaged while still green. Good contractors will wait for a spell of settled weather, and we do the same. Rain falling on fresh joints washes out the lime and weakens the surface.

Repointing seldom stands alone. The mortar cap round the pots, called flaunching, and the lead flashings where the stack meets the slope are exposed to the same weather and fail on a similar timescale. If you repoint the brickwork and ignore a cracked cap, the stack can stay wet, and the damp patch on the breast returns.

Our pages on chimney flaunching and why a chimney leaks help you work out which part is the real source. Each part is checked at the survey and photographed, so you see what we saw.

Where only one part has failed, the quote covers only that part. If the flashing is the problem, new pointing on the brickwork will not stop the leak. If the pointing is the problem, replacing the lead is a waste of money.

The mortar cap and the pots

Pots that sit loose in cracked flaunching are best rebedded at the same time. It takes little extra work with the access already in place, and it saves a second visit.

Several errors turn up again and again on repointed stacks. The first is filling over the old mortar without raking out, which gives a neat finish for a short time. The second is a mix that is too strong for the brick, which stops the joints from moving with the stack and sends the damage into the brick faces. The third is mortar that is too wet and shrinks as it dries, leaving hairline gaps that let water straight in.

A fourth is skipping the preparation of the bricks. Dry, dusty brick pulls the water out of fresh mortar so quickly that it never cures properly. Brushing and damping the joints before filling is a small step that makes a real difference.

Why a cheap-looking repoint can cost twice

If any of these mistakes are made, the pointing usually fails within a few winters, and the stack is back to square one with more damage. For that reason, we look at how the existing pointing failed before choosing the repair. A stack that has lost its mortar in a pattern, such as always on the south-west face, tells us which weather is doing the damage.

Fresh pointing is not finished the day it goes in. Lime mortar in particular cures slowly by taking in carbon dioxide from the air, and it needs protection from rain, hard sun and frost during that time. On an exposed stack, hessian or a cover is sometimes used for the first few days.

It is normal for new mortar to look different from old for a while. Colour evens out as it dries and weathers. Hairline shrinkage cracks that appear in the first weeks should be looked at, but fine cracking is not unusual in a mortar that has not fully cured.

Once the last joint is finished we sweep the roof, clear the site and take the waste with us. Photographs of the finished stack come to you, and the work sits under our written 10-year workmanship guarantee. A good habit is to look at the stack from the ground after the first heavy rain, and again before the next winter. If a damp patch inside returns, tell us, because it points to a cause other than the pointing.