Wrong mortar causes more damage than the original soiling. Hard cement on soft brick, incorrect joint profiles, colour mismatches — we see the consequences daily. And we see buildings where correct lime repointing has protected the fabric for fifty years without issue.
Mortar joints are not just the gap between bricks or stones. They are the sacrificial layer of the wall — designed to be softer than the masonry units, to accommodate movement, and to allow moisture to escape. When this balance is wrong, the masonry pays the price.
Hard Portland cement mortar, used extensively from the 1970s onwards on Victorian and Georgian buildings that were never designed to receive it, creates a closed system. Moisture that enters the wall cannot escape through the mortar joint. It escapes through the brick face instead, carrying salts with it, and the result is spalling — the surface of the brick or stone detaching in flakes. On London stock brick, this damage is irreversible.
Lime mortar — specifically a non-hydraulic or feebly hydraulic lime mix specified to match the original — behaves as the wall was designed. It's softer than the masonry units. It breathes. It can be raked out and replaced without damaging the surrounding fabric. It's the correct material for any pre-1900 building, and the only material we specify for listed buildings.
Raking out. Defective mortar is carefully removed to a depth of at least 20mm using angle grinders or oscillating tools. For listed buildings and soft brick, hand tools only — angle grinders can cause irreversible damage to brick arises if used carelessly. The depth matters: shallow repointing fails quickly and hides water ingress behind a cosmetic joint.
Mortar specification. We specify the mortar mix based on the existing material: a laboratory analysis of original mortar is carried out on conservation projects; on standard projects, we assess the original by eye and specify accordingly. Aggregate colour, mix ratio, and set strength are all part of the specification. On listed buildings, the mortar is submitted to the conservation officer for approval.
Joint profile. The shape of the finished joint matters both aesthetically and structurally. A struck joint, a bucket handle, a flush joint — each has appropriate uses and each behaves differently in terms of weather resistance. We replicate the original joint profile unless there's a specific reason not to.
Colour matching. In conservation areas and on listed buildings, the mortar colour must match the original as closely as possible. This is achieved through aggregate selection and sometimes through the addition of natural pigments. We carry out sample panels for approval before full works proceed.
On listed buildings, all mortar work requires conservation officer approval. The specification — mix design, joint profile, colour, method of raking out — is submitted as a method statement. We manage this process as part of our service.
Hard cement repointing on a listed building without consent is a listed building consent offence. If you've inherited a building that has been badly repointed, we can advise on a phased programme to correct it — the work can be carried out over time as sections of mortar fail naturally.
Repointing costs depend on the area to be treated, the access required, and the mortar specification. A typical Victorian terrace rear wall might start from £1,500–£3,000. Listed buildings and conservation areas requiring colour-matched lime mortar cost more. We provide written quotes within 48 hours of a free site survey.
Lime mortar is softer and more flexible than cement, which allows it to accommodate the natural movement of old masonry without cracking. It's also vapour-permeable — moisture can move through it rather than being trapped in the wall. Hard cement mortar on soft old brick or stone locks moisture in, accelerates decay, and eventually causes spalling. On any pre-1900 building, lime mortar is almost always the correct specification.
Correctly specified lime mortar repointing on a well-maintained building should last 30–50 years or more. Hard cement repointing typically fails sooner, because the differential movement between the hard mortar and the soft masonry units causes fractures at the masonry face rather than in the joint.
Lime mortar repointing should not be carried out in freezing temperatures — the mortar needs to cure without freezing. We generally advise against repointing work between November and March unless weather conditions can be controlled. Cement mortar is less sensitive but still requires minimum 5°C.