Period brickwork is rarely as rigid as modern construction. Historic bricks are softer, more porous and less uniform, laid with lime mortars that let the wall breathe and move with the seasons. Cement-based pointing is hard, brittle and largely impermeable. It traps moisture inside the brickwork, encourages frost damage and can spall the faces of the bricks. Lime mortar is softer, more flexible and sacrificial, so minor movement is absorbed by the mortar rather than the bricks. It also lets water vapour escape, allowing walls to dry after driving rain.
Good pointing begins long before the first trowel of mortar goes in. Rake out the old mortar to a depth of at least two and a half times the joint width, and no less than 15mm. On a typical 65mm brick with a 10mm joint, that means removing 20–25mm. This gives the new lime something to key into and prevents a shallow, cosmetic skimming.
Use a plugging chisel and lump hammer, working along the joint rather than hammering straight into the brick. Angle grinders can be used with care, but they remove material quickly and easily damage arrises. Once raked, brush out all dust and debris. If the bricks are highly absorbent, dampen the joints with a fine mist of water before pointing. Do not soak them; the aim is to stop the new mortar drying out too quickly.
Traditional lime mortar for pointing is usually based on lime putty or natural hydraulic lime, mixed with a well-graded sharp sand. A common mix is one part lime to two and a half or three parts sand by volume. Avoid soft builder’s sand and any sand containing clay or silt; these weaken the mortar.
The finished mix should be soft, cohesive and just able to hold its shape on a trowel. If it slumps or runs, it is too wet; if it crumbles or drags, it is too dry. Add water sparingly and mix thoroughly. A good test is to roll a ball in your hand: it should hold together without leaving a greasy film. Let it stand before use, then knock it up again without adding more water.
Dampen the raked joints once more, then press the mortar firmly into the joint in thin layers rather than one thick fill. A small pointing trowel or a hawk and trowel works well. Push the mortar into the joint with the edge of the trowel, filling from the bottom up, and avoid smearing it across the face of the bricks. Any mortar that lands on the brickwork should be left to dry slightly before being brushed off with a churn brush; wiping it wet only spreads lime into the pores.
Once the mortar has firmed up, tool the joint. The traditional test is to press with your thumb: it should feel firm but still leave a slight impression. Use a jointing iron, a wooden stick or a shaped piece of metal to compress the mortar and create a neat profile. For most period brickwork, a flush or very slightly recessed finish is appropriate. Avoid deeply recessed joints, which trap water, and avoid over-polishing the surface, which can draw the lime to the face and weaken the joint. Work in small areas and keep the joints full and consistent.
New lime mortar does not cure by drying alone; it needs moisture and air to carbonate and gain strength. Protect fresh pointing from direct sun, drying wind and heavy rain. Damp Hessian draped over the wall, or plastic sheeting fixed clear of the surface, will help. Mist the mortar gently for the first three to seven days in warm weather. Do not let it freeze, and do not work below about 5°C or when frost is forecast.
Spring and early autumn are usually the best times for pointing. In summer, work early or late in the day and keep the wall shaded if possible. In winter, use protective sheeting and accept slow progress. Lime mortar gains strength over weeks and months, so do not judge it on the first day.
Small hairline cracks can appear as lime mortar dries, especially if the mix was too wet or the wall dried too quickly. They are usually harmless and can be left to weather. If joints crumble or fail, the likely causes are a mortar that was too strong, too dry or applied in unsuitable conditions. Repointing is not a one-off job; it is part of the long-term maintenance of a historic building. Inspect the brickwork every few years, deal with failed joints before water gets behind them, and match the new mortar to the old in colour, texture and strength.
Lime pointing is slow, patient work, but it is one of the kindest things you can do for a period property. Done well, it lets the bricks breathe, sheds water and settles into the wall rather than fighting it. The result is not a pristine modern finish, but something far better: brickwork that looks right, behaves well and will last for generations.
Lime & Stone Journal shares practical, down-to-earth guidance on lime plastering and historic building restoration for readers across the UK.
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