Your chimney stack is exposed to the harshest weather conditions of any part of your home. It sits above the roofline, facing rain, frost, wind, and sun, day after day, year after year. The mortar joints between the bricks are the most vulnerable part — and once they start to deteriorate, water can begin to penetrate the stack, causing damage that spreads well beyond the chimney itself.
Repointing is the process of raking out old, damaged mortar and replacing it with fresh mortar. It's a relatively straightforward job for a qualified roofer with the right equipment, and it costs a fraction of what you'll spend if you leave it until bricks start falling or damp penetrates the breast inside your home.
Here are the five warning signs that your chimney needs repointing now, not later.
1. Crumbling or Recessed Mortar Joints
This is the most obvious sign and the one that most clearly indicates repointing is overdue. If you can see that the mortar between the bricks has crumbled away, or has receded significantly from the face of the brickwork, the chimney stack is no longer properly waterproofed.
Mortar starts to fail due to freeze-thaw cycles. Water seeps into hairline cracks, freezes and expands in winter, and gradually breaks the mortar down. Once the mortar face is recessed by more than 5mm to 10mm, water will sit in the joint rather than run off, accelerating the process.
You can often spot this from ground level with a pair of binoculars. Look for joints that appear hollow or dark compared to the rest, or areas where pieces of mortar are missing altogether. If you're in any doubt, a roofer can inspect from the roof level and give you a definitive assessment.
2. Damp Patches on the Chimney Breast Inside
If you notice damp patches, tide marks, or peeling wallpaper on the chimney breast wall inside your home — particularly in a bedroom or on a first-floor ceiling — it's a strong indicator that water is getting into the chimney stack and tracking down through the structure.
This kind of damp is distinct from condensation. It tends to appear after prolonged wet weather, may have a brownish or yellowish tint from the mortar it's passing through, and doesn't disappear with ventilation. Left untreated, it can cause plaster to blow, timber in the breast to rot, and mould to develop behind the wall surface.
If the damp is appearing on the chimney breast, the problem has already progressed beyond early stages. Repointing the stack will stop further water ingress, but the interior damp damage may need separate attention once the roof work is done.
3. White Staining on the Brickwork (Efflorescence)
White powdery deposits on the face of your chimney bricks — known as efflorescence — are caused by soluble salts being drawn out of the brickwork as water passes through it and evaporates on the surface. It's a reliable indicator that moisture is actively migrating through the masonry.
Efflorescence itself won't damage the bricks, but it tells you that water is getting in somewhere. On a chimney stack, that somewhere is almost always the mortar joints. If the joints are allowing water ingress and you're seeing white staining on the brickwork face, repointing should be done as soon as practical to prevent ongoing saturation of the masonry.
4. Loose or Shifting Bricks
If any bricks in your chimney stack feel loose, have shifted out of alignment, or — in serious cases — have fallen off entirely, the situation has moved beyond routine repointing and requires urgent attention.
Loose bricks are a safety risk, particularly for a stack above a public pavement, a conservatory roof, or a neighbouring property. A falling chimney brick can cause serious injury or significant property damage. If you notice any shifting or movement in the stack, treat this as urgent and arrange an inspection immediately.
The remedial work will typically involve repointing and may also require some bricks to be relaid. In some cases — particularly for tall or heavily deteriorated stacks — partial or full chimney removal may be the safest and most cost-effective solution, especially if the fireplace is no longer in use.
5. Damaged or Failing Lead Flashing
The lead flashing around the base of your chimney where it meets the roof is a critical waterproofing junction. It seals the gap between the stack and the surrounding tiles, preventing water from running down behind the chimney and into the roof structure.
Over time, lead flashing can lift, crack, pull away from the mortar joints, or corrode. You might notice this from the ground as a visible gap between the flashing and the brickwork, or you might only discover it when water staining appears on the ceiling below. Chimney flashing failures are one of the most common causes of localised roof leaks in older Hampshire homes.
When a roofer visits to repoint your chimney, they should always inspect the flashing too. If the flashing is in poor condition, it makes sense to repair or replace it at the same time as the repointing — since you already have access to the stack and scaffolding in place, combining the work keeps costs down.
When Should You Call a Professional?
Chimney work requires safe access to the roof and the stack — which means scaffolding in most cases. It's not a job for ladders alone, and it's certainly not a DIY job. Using the wrong mortar mix for repointing (a common mistake) can actually accelerate damage to older bricks by being too hard and rigid, so it's important the work is carried out by someone who understands the materials involved.
If you've spotted any of the five signs above, the next step is a professional inspection. CMW Repairs Ltd carries out chimney inspections, repointing, flashing repairs, and full or partial stack removals across Hampshire and Southampton. Find out more about our chimney repair services, or contact us to arrange an inspection.