Repointing near you

Historic England's method is to find the mortar rather than to specify one from a catalogue. Look for a sound example of pointing in a sheltered part of the building — under the eaves, behind downpipes, on north and east elevations — that is contemporary with the original construction, and inspect it closely for how the joint is finished and whether the aggregate is coarse or fine, along with any other additions such as ash, broken brick or shell that contribute to its character. For domestic buildings constructed before the early twentieth century, that mortar will almost certainly be lime-based rather than cement. Care is needed not to copy a later, inappropriate repair by mistake.

There are two families of lime. Non-hydraulic lime is the most permeable of all binders, hardens slowly by reacting with carbon dioxide in the air, has good adhesive properties, can accommodate some movement, and suits sheltered locations or soft permeable masonry and brick; it comes as lime putty or as powder, and lime putty and lime putty mortars can be stored indefinitely in airtight containers protected from frost. Natural hydraulic lime sets by chemical reaction with water as well as by carbonation, is supplied in three strengths — NHL2, NHL3.5 and NHL5 — and has lower permeability and higher compressive strength than non-hydraulic mortars, which makes it appropriate where a location is permanently wet or very exposed. Pozzolanic additions such as finely ground brick dust give a non-hydraulic mix a faster strength gain with slightly less permeability; cement is not a suitable additive for a lime putty mortar.

Mixes vary considerably with circumstances, from pure lime putty with no aggregate to one part binder to three parts aggregate, and the strength also has to relate to exposure, with parapets and chimney stacks usually needing relatively stronger mixes than sheltered areas. Approved Document C makes the same point in building regulations language for rendered solid walls: the strength of the mortar should be compatible with the strength of the bricks or blocks. Where a building is particularly significant, a sample can be sent for analysis to identify the original aggregates and binders.

Defective pointing should be carefully raked out manually with hooked tools or masonry chisels to a depth of at least twice the height of the joint, and on rubble stonework often much deeper than that; on stonework with variable joint widths, the roofer or mason first has to decide what the average joint width is. For finely jointed work, which Historic England notes is rarely in need of repointing at all, a hand-held saw blade is a suitable tool. Whatever the method, mortar must be removed from the top and bottom of the joint to leave a square-cut joint, dust and debris cleared with brushes or a vacuum and rinsed with water so no loose dry material remains, and the masonry thoroughly dampened with a spray before the mortar goes in, to reduce suction, improve adhesion and stop the mortar drying too fast.

Power tools are the problem. Historic England does not recommend using angle grinders to remove pointing, because they do not completely remove old mortar from the joints, can easily damage the face of the masonry, and create so much dust that it is very difficult to keep track of where the blade is. The exception it allows is narrow: where there is hard cement-rich mortar, a thin diamond-disc cutter may be used very carefully to make an initial breach along the centre of wide joints so that the loose mortar can then be removed with a hammer and sharp chisel without damaging the corners of the masonry, or a masonry drill can be used to drill a line of holes along the centre of the joint for the same purpose.

The work is also weather-dependent in a way that surprises people. Work with lime mortars should be avoided during extremes of temperature, very cold or very hot days, or very windy weather, and is best done in spring, summer or early autumn. Protection from sunshine, rain and wind is needed during the work and at completion to prevent rapid drying that would damage the mortar before it sets properly, and frost protection is needed if work has to be done in winter. That is why a competent firm hangs hessian and works to the forecast rather than to the diary.

A masonry wall regulates water: it absorbs some rain and releases it again once the weather dries. The joint does two jobs in that system — it keeps rainwater out of the core of the wall, and it provides the most effective route for moisture already in the wall to get back to the atmosphere. Historic England's guidance describes what happens when that route is closed: if the joints cannot release moisture, as occurs when hard cement mortar is used, all the moisture movement is concentrated in the bricks or stones, which increases the chance of frost damage and of damage from the crystallisation of soluble salts.

The visible result is a wall where the pointing looks perfect and the masonry is falling apart: brick faces spalling away, stone going soft and powdery, and a grid of hard mortar left standing proud of the units it was supposed to protect. Historic England's illustrated examples of poor repointing include cement mortar on rubble stonework cracking and thereby trapping moisture and accelerating decay, and damage to soft brickwork caused by the use of cement mortar.

Removing bad cement pointing is worth doing, but not at any price. The guidance is that mortar of this type should only be removed if that can be done without causing even more damage to the adjoining masonry — which is a judgement to be made on the wall, joint by joint, rather than a decision to be taken from a quotation. Where cement has to come out, the technique matters more than anywhere else in the job.

Historic England's practical advice starts before the contractor. Where masonry is clearly decaying, the true cause should be identified so the correct remedy can be chosen: the pointing may not be the cause at all, so the condition of the whole structure should be reviewed along with the severity of exposure, and any defect contributing to the deterioration should be remedied before repointing is carried out. It recommends an independent condition survey of an older property by a professional such as an architect, surveyor or architectural technologist familiar with older buildings, ideally one accredited in building conservation, rather than going directly to a building contractor.

For more extensive work, and for historically significant buildings such as listed buildings or those in a conservation area, it suggests the help of a surveyor or architect to specify and oversee the work — an expense that avoids more expensive mistakes and failures. Its own guidance also notes that the local planning authority should be contacted well before the planned start date to establish what is required, since consent obligations vary with the degree of planning control in place. Listed building consent and conservation area constraints are covered elsewhere on this site, but repointing changes the appearance of a whole elevation, which is precisely why it is asked about.

Samples are the mechanism that keeps everyone honest. Mortar patties or biscuits allow the mix to be agreed before any work begins and can be left in place as the standard the work should meet; on listed buildings and ancient monuments they may be required as part of the consent process. Once the samples are agreed, a trial panel of repointing should be done in a discreet area, properly finished and allowed to dry, so the final appearance can be judged before the whole elevation is committed. Scotland has its own heritage guidance, including Historic Environment Scotland's INFORM guides on repointing rubble stonework and on lime and cement in traditional mortars.

Repointing is priced on removal, on access and on the mortar, in that order. What moves a figure is how much of the elevation genuinely needs doing rather than how much is being offered, whether the existing mortar is soft lime or hard cement that has to be cut out carefully, the joint width and the masonry type — rubble stonework takes far longer than regular brickwork — the height and how the wall is being reached, the mortar specification and whether samples and a trial panel are required, the joint finish being matched, and the weather protection needed while a lime mortar cures. Heritage constraints can settle several of those before anyone measures.

LokalMatch is the introduction and no more. Describe the wall once with your postcode — its age, the material, how much of it is affected and whether the building is listed or in a conservation area — and masonry firms working in your area will get in touch. Homeowners are never charged to post a request, because the businesses pay for the requests they receive. LokalMatch does not repoint walls, does not set prices, and does not vet, rank or recommend anyone, so comparing what each firm proposes to use and how they propose to cut the old mortar out is the part that matters and the part that is yours.