Chimney Repointing in Yorkshire — What Goes Wrong and How to Fix It

• 30 Jun 2026
• 4 min read

Chimney stacks are the most exposed part of any building. Four faces of masonry in permanent contact with rainfall, frost, wind and thermal movement — with no roof overhang to protect them. When the pointing fails on a chimney, water gets in fast, and the damage it causes is not limited to the chimney itself.

Why Chimney Pointing Fails Faster Than Wall Pointing

The pointing on a chimney stack faces conditions no other part of the building has to deal with:

• Constant wet/dry cycling — exposed from all sides, chimneys absorb rain and dry out repeatedly. Each cycle stresses the mortar joints.
• Freeze-thaw at height — water trapped in open joints expands when it freezes. At stack height, exposed to wind chill, freeze-thaw is more frequent and more severe than at ground level.
• Thermal movement — flue gases heat the internal face; rain cools the external face. This differential expansion weakens mortar bonds over time.
• No maintenance access — most chimney stacks go uninspected for years. By the time failure is visible from the ground, the pointing is usually badly eroded.

How to Spot Failing Chimney Pointing

From ground level, look for:

• Mortar joints that appear recessed or dark — eroded mortar holds moisture and looks permanently wet
• White staining on the stack face — efflorescence from water moving through open joints
• Visible gaps or cracks in the pointing, particularly on the north or east face
• Damp patches on the chimney breast inside the property — a clear sign water is tracking down through the stack
• Loose or missing mortar at the haunching (the mortar fillet around the base of the pot)

A building leak and damp inspection will confirm whether the chimney is the source of internal damp — it is often misdiagnosed as rising damp or condensation when the actual entry point is the stack.

Cement vs. Lime on Chimney Stacks

This is one of the most consequential decisions in chimney repointing. On a pre-1920 brick or stone chimney, cement mortar is the wrong specification. The reasons are the same as for any heritage masonry — cement is stronger and less flexible than the surrounding material — but the consequences are accelerated at chimney height because of the extreme exposure conditions.

Cement-pointed chimney joints tend to fail by pulling away from the brick face rather than eroding gradually. This leaves a gap on one edge of the joint — often invisible from below — which funnels water directly into the wall. On a chimney built with soft handmade bricks or Yorkshire sandstone, this leads to spalling and permanent face damage.

For pre-1920 stacks, the correct specification is NHL 3.5 hydraulic lime mortar, matched to the original aggregate and colour where possible. This is what NSJ specifies and applies for heritage chimney work across Ilkley, Harrogate, Saltaire and Bradford.

For post-war brick stacks, a sand and cement mix at the correct ratio and profile is appropriate — but it must be applied correctly, not squeezed over the existing joint face.

What Chimney Repointing Involves

Proper chimney repointing is not a quick job. To do it correctly:

1. Access — scaffold, cherry picker, or roof ladder depending on stack height and position
2. Raking out — old mortar removed to a minimum depth of 15–20mm using an angle grinder or plugging chisel. The joint must be clean and sound before new mortar is applied.
3. Damping down — the masonry must be dampened before mortar application to prevent suction pulling moisture from the mix too quickly
4. Application and finishing — mortar applied in layers if required; finished to match the original joint profile
5. Curing — lime mortar in particular needs protection from rapid drying in hot or windy conditions

The haunching and flaunching (the mortar bedding around the chimney pots) is checked and repaired at the same time. This is a common water entry point and is often neglected when only the pointing is quoted for.

When to Book a Chimney Inspection

Do not wait until you see damp on the chimney breast inside. By that point the water has been finding its way through for months or years. If your chimney stack has not been inspected or repointed in the last 10–15 years, it almost certainly needs attention.

NSJ carries out chimney repointing across Bradford, Leeds, Harrogate, Ilkley, Otley, Skipton, Wetherby, Halifax and Saltaire. We specify the correct mortar for the building type, rake out properly, and do not apply new mortar over old. Contact us to arrange an inspection or quote.