Stone repairs and lime repointing in Scotland

Scottish sandstone is often soft and laid in beds, so it delaminates and flakes as water gets between the layers. Shallow decay can be dressed back to a sound face. Deeper decay is cut out and indented with new stone, or built up with a lime-based stone repair mortar where a small area is involved.

Where a stone has decayed too far, we cut it out and replace it, either as a whole stone or as an indent set into the sound part of the original. New stone is cut to the profile and dressing of the stones around it, so the repair reads as part of the wall.

Stone is sourced from UK quarries to match the original in colour, grain and bed. Mortar is matched for colour, aggregate and strength against the existing building, so new pointing does not stand out or behave differently from the old.

Boundary walls, garden walls and retaining walls bulge and collapse when water and roots get into them or when the ground behind pushes them over. We take down the failed section, salvage and clean the stone, and rebuild it on a sound base, adding drainage behind a retaining wall where water is the cause. On a stone boundary wall rebuild we built a new masonry backing, then rebuilt the face in natural stone and finished it with stone coping.

Lime mortar is softer and more permeable than the stone it sits between. Water evaporates out through the joints, and any movement or decay happens in the mortar, which is cheap to renew. Cement mortar is harder and less permeable than most stone, so moisture leaves through the stone instead, carrying salts that break down its face. That is why stone repointed in cement often decays faster than it did before.

We rake out failed and cement mortar by hand to a sound depth, clean and dampen the joints, and repoint in lime, finishing the joint to suit the stone. On a traditional stone gable we removed the ivy and failed mortar, installed crack stitching bars, tied the chimney back and repointed the whole elevation in lime. On a traditional stone cottage we repaired and repointed sections of the rubble stone walls, keeping the character of the original construction.

Older brick buildings were laid in lime too, and the same rules apply. On The Coach House in Perth we repointed the red brickwork throughout in Mason’s Mortar lime mortar.

A typical gable elevation in lime mortar takes 2 to 4 weeks, depending on its size, the weather and the surface preparation. Lime must be protected from frost, rain and strong sun while it sets, which the programme allows for.