Ashlar

Ashlar, in Turkish kesme taş, is building stone that has been dressed after quarrying so that its faces and edges are flat and square, giving it a prismatic shape. Ashlar walls run in level courses with thin joints and a regular face. The exposed face may be left smooth or worked with claw, point or bush hammer finishes; in some examples the edges are drafted in a margin while the centre is left rough.

Its role in the building

Ashlar is used on the facades of monumental buildings, in arches, domes and vaults, in portals and at corners. Flat bedding faces transfer load between stones more safely, and voussoirs, keystones and springers can be cut to the required geometry. Many historic walls are not solid ashlar at all: the inner and outer faces are ashlar while the core is filled with rubble and mortar. Understanding the difference between the visible face and the wall section is the first step in understanding how the structure behaves. Stones tied together with iron or lead-set cramps are also common.

Ashlar in survey and restoration

A stone-by-stone survey drawing shows every block with its joint lines, while stone type, surface tooling and decay are mapped on separate sheets. Erosion, scaling, cracking and corroding cramps are the usual problems. Where replacement is needed, new stone is chosen to match the original in type, colour, porosity and tooling, but is applied so that it can be recognised as new on close inspection. Photogrammetry and laser scanning are the most efficient ways to produce scaled orthophotos and 3D models of ashlar facades.