Masonry near you

Mortar is meant to be the sacrificial part of a wall. It is the bit that takes the movement, carries moisture out to the face and is renewed every few generations, while the bricks or stones stay put. That only works if the mortar is weaker than the units it beds. On an older solid wall, which is typically built in lime, a hard cement repointing reverses the relationship: the wall still moves and still gets wet, but now the weakest thing in it is the face of the brick or stone, and that is what breaks off.

It also changes how the wall dries. A solid wall handles rain by absorbing some of it and releasing it again, and a permeable lime mortar gives that moisture a route back out. Seal the joints with something dense and the water leaves through the masonry face instead, taking dissolved salts with it and pushing the surface off in frost. This is why conservation practice on older and historic buildings is to repoint in a lime mortar matched to the original, and why a quotation that specifies one mix for every house on the street is a warning sign.

None of this makes cement wrong. On a modern cavity wall built in cement, in a mix matched to the existing, cement mortar is exactly right. The skill being bought is knowing which building is in front of you, and being able to explain the choice rather than reaching for whatever is in the van.

Cracks are the common call, and the useful distinction is between a crack that has stopped and one that is still moving. Fine cracking that follows the joints, is stable through the seasons and appears at a change of material is usually old movement that has found its position. A crack that steps diagonally through the brickwork, is wider at one end, opens in a dry summer and closes in a wet winter, or runs through the units rather than around them, is telling you about the ground or the structure, and it needs a structural engineer's opinion before any mason fills it.

Wall tie failure is a particularly British problem in cavity walls of a certain age, where the metal ties corrode, expand and lift the outer leaf, showing as regular horizontal cracking at roughly the tie spacing and sometimes as a bulge in the elevation. Bulging and bowing also show up on solid walls where the bond has separated, and a wall that is no longer flat is a structural matter rather than a cosmetic one.

Then there is water, which is behind most of the rest. Failed rainwater goods soak one patch of wall repeatedly, ground levels raised above the damp-proof course let moisture bypass it, and a hard cement render or repointing stops the wall drying. The Planning Portal describes a damp-proof course as installed in a building to prevent rising or penetrating damp, creating a layer which prevents moisture from entering the walls, and Approved Document C is the England guidance on the resistance to moisture of floors, walls and roofs with examples of damp proofing and ventilation provisions.

Structural masonry is squarely within the Building Regulations. Approved Document A is the England guidance covering the loadings on a building and the construction of the structural elements including the foundations, walls, floors, roofs and chimneys, so cutting in a beam, forming an opening, underpinning or rebuilding a load-bearing wall is building control work rather than maintenance. GOV.UK sets out the two routes for approval: a building control body, being your local authority's building control department or a private registered building control approver, or someone registered with a competent person scheme. Without approval you will not have the certificates of compliance you may need when you want to sell your home.

On a terrace or a semi, the Party Wall etc. Act 1996 is the other half of the paperwork, and it applies in England and Wales. GOV.UK's guidance covers work to an existing party wall or party structure, building a new wall on or at the boundary of two properties, and excavation near to and below the foundation level of neighbouring buildings, and requires notice to adjoining owners. Section 3 requires a party structure notice at least two months before the work begins. Section 6 catches excavation within three metres of a neighbour's building where the work will go deeper than the bottom of their foundations, and within six metres where it would meet a plane drawn downwards at forty-five degrees, and requires at least one month's notice, with the adjoining owner's failure to consent within fourteen days counting as dissent.

Heritage and geography change things again. Listed building consent is required for works that affect a listed building's character as a building of special architectural or historic interest, and doing them without consent is a criminal offence. In Scotland the equivalent of building control is the building warrant, which mygov.scot lists as needed for building or removing load-bearing walls and for changing external walls or other structural elements, granted by the council's building standards department and valid for three years, with an offence and a possible fine for starting without one. Northern Ireland works to technical booklets, with Booklet D covering structure.

A competent mason starts with the cause. That means looking at ground levels, rainwater goods, the damp-proof course, the age and construction of the wall and the pattern of any cracking before pricing the repair, and being willing to say that the wall needs monitoring or an engineer rather than mortar. Rebuilding work then proceeds in sections with proper support: needles and props where a load is being carried, the bond honoured rather than faked, ties and lintels specified rather than improvised, and new work left to gain strength before the support comes out.

Materials are matched, not approximated. Matching a brick means matching size, colour, texture and, on an old wall, the fact that it was handmade; matching a mortar means matching the mix and the sand as well as the colour, and finishing the joint in the same profile as the original. Good work on an old elevation should be difficult to find a year later.

The health risk is the part that rarely appears in a quotation. HSE describes silica as a natural substance found in varying amounts in most rocks, sand and clay and a major constituent of construction materials such as bricks, tiles, concrete and mortar, with dust generated during common tasks including cutting, drilling, grinding and polishing, and heavy and prolonged exposure to respirable crystalline silica capable of causing lung cancer and other serious respiratory diseases. HSE also states that over 500 construction workers are believed to die from exposure to silica dust every year, and that regularly breathing construction dust can cause diseases such as lung cancer, asthma, chronic obstructive pulmonary disease and silicosis. A firm cutting brick or grinding out joints on your property should be controlling that dust at source and wearing suitable respiratory protection, not producing a cloud over the garden.