It is imperative that incompatible repair materials are not used so that further damage to the fabric of the structure can be avoided. The old adage of ‘stronger is better’ is largely inaccurate when applied to the concept of conservation and repair of stone, although in the past it was widely accepted as a logical approach in the selection of repair materials. Stifling the ability of traditional stone buildings to breathe, the use of cement based mortar has accelerated the rate of decay amongst many of the country’s historic structures.
In contrast, the flexible and less brittle lime mortars are permeable to water vapour allowing moisture which builds up inside a building to migrate harmlessly through the fabric.
Before embarking on a programme of stone repairs, various factors should be considered, such as the extent of the damage or deterioration, and how necessary is a repair – whilst structurally integral repairs should be prioritised as a matter of safety, it may sometimes be preferable to leave other elements to slowly decay as part of far longer cycle of periodic renewal.