How to repair a brick wall

Brick wall repairs carried out correctly protect a property for decades. Carried out incorrectly, they can accelerate the very deterioration they were intended to stop. The most widespread cause of poor brick wall repairs in London is the use of Portland cement mortar on period buildings that were built with lime mortar. Cement is significantly harder than the surrounding Victorian or Edwardian brick. Rather than accommodating the natural movement of the wall as lime mortar does, cement mortar forces that movement into the softer brick body, causing the brick faces to crack and spall. This is a well-documented and entirely avoidable mistake that is responsible for a significant proportion of deteriorating brickwork seen on London period properties.

Repointing: when it is needed and how it is done

Repointing is the process of removing deteriorated mortar from the joints between bricks and replacing it with fresh mortar. It is needed when the existing mortar has cracked, crumbled, receded below the brick face, become porous or shows signs of active moisture ingress. On London period properties, repointing should be carried out approximately every 50 to 70 years as lime mortar naturally weathers over time, though this varies significantly with the level of exposure and the original quality of the pointing.

The process requires raking out the old mortar to a minimum depth of 20mm. Using an oscillating multi-tool with a dust extraction attachment on period brickwork is preferable to a disc cutter, which cannot be used close to brick edges without the risk of damaging the arises. All loose material is removed, the joint is flushed with water and the new mortar is applied in layers, compacted firmly and tooled to the correct profile. Matching the original joint profile is important aesthetically and practically. Flush or recessed profiles perform differently from weather-struck profiles in terms of water shedding.

Replacing damaged or spalled bricks

Where individual bricks have spalled, cracked through or deteriorated beyond the point where repointing alone is sufficient, they must be cut out and replaced. The process for replacing a brick in an older London wall involves cutting the mortar joints around the affected brick carefully to avoid disturbing adjacent bricks, removing the brick in sections if necessary, preparing the opening by removing all old mortar back to clean sound masonry and fitting the replacement brick in fresh lime mortar.

Sourcing a replacement brick that matches the original is critical. Modern factory-produced bricks look distinctly different from Victorian stock brick, with different dimensions, colour variation and texture. For period properties, the best match comes from reclaimed Victorian brick salvaged from demolition, which reproduces the appropriate character. The joints around the new brick are then pointed to match the surrounding wall. Where significant areas of replacement are needed, cleaning the entire facade before repair work ensures a consistent appearance after restoration.

Why brickwork should be cleaned before repair work begins

Professional brick cleaning is almost always the correct starting point before any repointing, brick replacement or restoration work. The reasons are both practical and structural. Mortar applied to dirty brickwork forms a weaker bond with the brick surface than mortar applied to clean brickwork, which reduces the lifespan of the repointing. Dirt and biological contamination in the mortar joints compromise adhesion further. Cleaning also reveals the true extent of the damage, allowing the contractor to assess which bricks need replacing, which joints need repointing and the overall condition of the facade before any work begins. Attempting repair on a dirty wall risks missing damage that is obscured by contamination and spending money on work that produces an uneven result visually and structurally.