Why lime matters on older houses
Most houses built before the 1920s were laid with lime mortar rather than cement. Lime is softer and more flexible than cement, and it lets moisture move through the joints and evaporate. In a solid brick wall that matters: the wall gets wet in the rain and dries out through the mortar, which acts as the weak, breathable part of the wall.
When an old wall is repointed with hard cement mortar, that balance is reversed. Moisture is trapped in the bricks, which then freeze and lose their faces; the hard joints do not move with the wall, so cracks run through the bricks instead of the mortar. Spalled bricks next to bright, hard cement joints are a very common sight. Lime mortar repointing avoids that damage.
Is lime right for your wall?
As a general rule, lime pointing suits soft, older bricks, solid walls without a cavity, and listed or historic buildings. Modern, hard bricks in a cavity wall are usually pointed with a cement-based mix, although a lime-rich mortar is still kinder to many bricks. The aim is always the same: the mortar should be weaker and more porous than the brick it sits between.
If the wall was previously repointed in cement, the cement may need careful removal before lime can be used, and some bricks may already need replacing.
Choosing the mix
There are different kinds of lime. Natural hydraulic limes, sold in grades such as NHL 2, NHL 3.5 and NHL 5, set partly by reacting with water and partly by drawing carbon dioxide from the air; the higher the number, the stronger and faster-setting. Non-hydraulic lime putty and hot-mixed lime set more slowly and are softer still, and are often used on the oldest and most delicate work.
The grade is chosen to suit the bricks, the exposure of the wall and the season. A chimney or a garden wall facing driving rain may need a slightly stronger mix than a sheltered elevation. The sand matters just as much as the lime: its colour and grading decide how the joint looks and how well the mortar performs, so matching the existing mortar often involves trial mixes.
How lime mortar repointing is done
Failed mortar is raked out by hand or with careful use of tools to a consistent depth, usually around twice the height of the joint, without damaging the brick edges. Dust is brushed out and the joints are dampened so the dry brick does not suck the water out of the new mortar too quickly.
The lime mortar is pressed firmly into the joints in layers if they are deep, and finished to suit the building. Many older walls have a flush or slightly recessed joint, often brushed or lightly beaten back once the mortar has stiffened to expose the sand and give a soft, traditional look.
Curing and protecting the work
Lime needs looking after while it cures. It must not dry too fast in sun or wind, and it must be protected from frost and heavy rain. Work is usually covered with damp hessian or sheeting and misted with water for several days. That is why lime repointing is best planned for the milder months; working in frost risks the mortar failing.
Time and cost factors
Lime work generally takes longer than cement repointing because of careful raking out, slower setting and the need to protect the joints. The area, access and scaffolding, removal of previous cement pointing and any brick replacement all affect the cost. Our repointing cost guide explains these factors.
Our repointing service page describes how we carry out repointing on brick walls and chimney stacks, and we offer free estimates after looking at the brickwork.
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Questions people ask
Why use lime mortar for repointing?
Lime is softer and more breathable than cement, so older walls can dry out and move without the bricks cracking or losing their faces.
How long does lime mortar repointing take?
Longer than cement repointing, because raking out is careful and the mortar must be protected while it cures. Area, access and weather decide the timescale.
What affects the cost of lime pointing?
The area, removing old cement pointing, the lime and sand chosen, scaffolding and access, brick replacement and the time needed to protect the work.
Can lime mortar be used in winter?
It should not be laid when frost is likely, and it needs protection from heavy rain. Lime repointing is best planned for the milder months.