Traditional skills and modern magic

22 August 2017
Stonemasonry

​Chester Farm’s crumbling limestone walls are receiving much attention at present. The conservation and restoration of historic buildings require a particularly sensitive approach, especially when tackling structural issues. Any structural intervention has to make a minimal impact on the fabric of the building, preferably be reversible, and, at the same time, avoid making any visible alteration.

 

This picture shows the installation of Cintec anchors, a clever and invisible way of stabilising loose rubble and old walls. The anchor rod comprises a steel section within a mesh fabric sock which is inserted into the wall and a specially developed grout is then injected under low pressure. The sock restrains the flow, expanding and moulding itself into the shape and spaces within the walls and providing the mechanical bond.

This anchoring system dispenses with the need for unsightly plates on the exterior of the structure, creating an invisible mend which traditional repair anchors cannot achieve.

However our next picture shows that traditional skills are still a vital part of the restoration of the buildings. A team of stone masons, using lime mortars, are painstakingly working their way around the limestone walls, repairing as they go.

Stonemasons 

A fundamental characteristic of traditional construction is its ‘breathability’ and flexibility. Breathability is the ability of materials to absorb moisture and release it again as conditions change without causing long-term damage to the building itself.

Until the mid-19th century, stone buildings were pointed with lime putty or earth based mortars. Lime, when used in mortar, has a high degree of breathability. Coupled with ventilation through roofs, doors, and windows, it allows buildings to dry out through evaporation.

Much damage has been caused to historic masonry by the use of cement-rich mortar. Soft lime-based mortars are preferred because their elasticity allows slight movement and their porosity allows the wall to breathe. The mortar should ideally be weaker and more porous than the masonry in which it is placed. A cement-based mortar will force moisture to evaporate through the weaker stone causing much damage.


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