First let us look at the building material of a typical traditionally constructed property in the Saddleworth area of Greater Manchester. The walls of traditional properties are typically constructed of two leaves of stone with a rubble infill, the original mortar being of a lime base and the internal plaster, if applied, also being lime. Through stones were installed to tie the two wall structures together and improve stability.
This photograph showing damage caused to stonework through the incorrect use of an OPC cement-based strap pointing. The pointing to a wall is considered as sacrificial to the stone and should therefore always be softer. In this situation lime pointing should have been applied. Lime pointing is more vapour permeable (Porous) and more flexible, allowing faster evaporation and drying of the structure. It also has the ability, to some extent, to reseal small cracks, so preventing water ingress which results in frost damage.