How to Repoint a Chimney – DIY Guide
To repoint a chimney, rake out crumbling mortar joints to a depth of 15–20mm, brush clean, dampen the brickwork, then pack in fresh mortar mix and finish flush. Work from the top down and allow to cure fully before exposure to rain.
- Angle grinder with mortar raking disc
- Cold chisel
- Club hammer
- Pointing trowel
- Stiff-bristle brush
- Bucket and mixing paddle
- Safety harness and scaffold tower or hired scaffold
- Safety goggles and dust mask
- Mortar mix (3:1 sharp sand to cement or pre-mixed pointing mortar)
- Cement
- Sharp sand
- Plasticiser
- Clean water
- Tarpaulin or dust sheet
- Masking tape (for adjacent lead flashing)
Step-by-Step Guide
Set Up Safe Access
Chimney repointing requires working at height — a hired scaffold tower or full scaffold system is essential. Never rely on a ladder alone for chimney work. Check all platforms are stable and use a safety harness anchored to a fixed point. Our roofing guide covers access equipment in detail. Tell someone you are working at height before you start.
Rake Out Failing Mortar Joints
Use an angle grinder fitted with a mortar raking disc to remove old, crumbling mortar to a depth of 15–20mm on all four faces of the chimney stack. On narrow joints, switch to a cold chisel and club hammer to avoid cutting into the brick faces. Work systematically, top to bottom, and rake every joint — even ones that look intact — as hairline cracks allow water to track underneath. Wear safety goggles and a dust mask throughout.
Clean Down the Stack
Brush all raked joints firmly with a stiff-bristle brush to remove dust, loose grit, and debris. Pay particular attention to the corners where mortar tends to pack in. Vacuum or blow out any remaining dust from deep joints. A clean substrate is critical — new mortar will not bond to a dusty or loose surface and will crack back out within one or two winters. Learn how to fix a roof leak around a chimney if water has already penetrated the stack.
Mix and Apply the Mortar
Mix mortar to a 3:1 ratio of sharp sand to cement, adding a small amount of plasticiser to improve workability. The mix should hold its shape when squeezed but not crumble. Dampen the joints with clean water immediately before pointing — do not soak. Load a hawk and use a pointing trowel to pack mortar firmly into each joint in layers if the recess is deep, pressing each layer back before adding the next. Avoid hollow spots.
Finish and Profile the Joints
Finish each joint to match the existing profile — typically a slightly recessed bucket-handle or weatherstruck finish on a chimney stack to shed water. Run the rounded handle of the trowel or a jointing tool along horizontal joints first, then vertical joints. Keep the mortar face flush or very slightly recessed; a proud joint traps water against the brick and accelerates frost damage. Check all joints are fully filled with no voids before moving on. See our guide to repointing a brick wall for further detail on joint profiles and finishing technique.
Protect and Allow to Cure
Drape a tarpaulin loosely over the finished work if rain is forecast within 24 hours — do not seal it tightly as the mortar needs to breathe. In hot weather, mist the joints lightly with water once or twice during the first day to slow curing and prevent shrinkage cracking. Allow a full 24–48 hours before any rain exposure and at least 7 days before painting or applying any sealant. Inspect the finished joints from ground level once cured and touch in any minor cracks with fresh mix.
Frequently Asked Questions
How do I know if my chimney needs repointing?
Look for mortar that is recessed more than 5mm, crumbling, or missing entirely between bricks. Damp patches on interior chimney breast walls are a strong indicator that the stack joints are failing and water is tracking in. Our guide to fixing a roof leak explains how to trace the source.
What mortar mix should I use for chimney repointing?
A 3:1 sharp sand to cement mix with a small amount of plasticiser is suitable for most UK brickwork. Avoid high-cement mixes — they are too rigid and will crack away from the brick. For older or softer handmade bricks, a 4:1 or lime-based mix is more appropriate to avoid damaging the brick faces.
Can I repoint a chimney myself or do I need a professional?
This is rated Advanced because safe working at height is as much of a challenge as the masonry skill itself. If you are confident setting up and working safely from a scaffold tower and comfortable using an angle grinder, the pointing work itself is achievable. If you have any doubt about access safety, hire a professional roofer.
How long does chimney repointing last?
Well-executed chimney repointing with the correct mortar mix should last 20–30 years under normal UK conditions. Longevity depends on the quality of preparation, the mortar mix, and the severity of exposure — a fully exposed chimney on a coastal or hillside property will face more weathering stress.
Do I need to repoint the chimney flaunching as well?
Flaunching is the sloped mortar bed at the base of the chimney pot. If it is cracked or lifting, it should be repaired at the same time as repointing — water gets in through both. Our chimney flaunching repair guide covers the full process separately.
Apply mortar in two thin layers on deep joints rather than one thick pack — the first layer, pressed back to create a key, gives the finishing layer something solid to grip. A single thick application shrinks unevenly as it cures and almost always develops a hairline crack down the centre of the joint.
Sources
- HSE — Work at Height Regulations 2005: guidance for workers — hse.gov.uk
- Which? — Repointing brickwork: what you need to know — which.co.uk
- Historic England — Mortars, Renders and Plasters (Practical Building Conservation) — historicengland.org.uk
This guide is for general information only. Always work safely and follow manufacturer instructions. DIYnut accepts no liability for injury or damage arising from DIY work.
