The use of Portland cement for repointing the joints of old stone structures and walls can cause decay. Before 1919 buildings rely on such materials to seal walls and exclude moisture, the permeable lime mortars widely used for older walls allowed them to ‘breathe
Traditional lime mortar pointing weathers back to the stage repointing is needed but if this is done with impervious cement erosion of sandstone themselves occurs in preference as they become the most permeable part of the wall and suffer the greatest frost and salt action.
Strong, cement mortars also develop hairline cracks from shrinkage or, with old buildings on shallow foundations. Lime mortar is a better material allowing moisture to escape from the building correctly, any minor cracks that do develop will self-heal. Remember too that modern forms of joint finish associated with cement can form ledges, trapping water.
WHAT SHOULD I USE TO REMOVE CEMENT POINTING?
We suggest to use hand tools a hammer and chisel along with a pick to rake back the mortar joints 20mm – 25mm for new application of lime mortar. Disc cutters and speed up the work if extreme care is taken not to damage the stonework in the process.
WHAT SHOULD WE REPLACE THE CEMENT POINTING WITH:
We suggest on building throughout Edinburgh to use a soft lime mortar like saint astier natural hydrated lime mortar a weaker and more permeable lime mortar that matches the colour, texture and profile of any surviving lime pointing