Stone masonry can be an important component of varieties of construction work. Stones can be used in dams, barrages, harbours, retaining and ornamental walls, buildings etc.
Good quality stones should be strong, durable, hard and heavy. For building construction they should be fire resistant and pleasing in appearance as well. Stones used for heavy construction or high load bearing work must be tested for strength, ie compressive strength test, in laboratory. For ordinary work, a heavy, unporous stone with smooth texture can be seen as a reasonably strong one. Ideally, a stone having specific gravity of 2.5 or little more may be regarded as a good building stone.
A strong stone may not necessarily be a hard one as well. It needs to be hard in order to be able to withstand abrasion, especially when used in pavements, floors and suchlike elements. While hardness is tested by Mohr’s scale of hardness, one also can have a reasonable idea of it by scratching the surface of a stone by a pointed or sharp metal piece. The surface should show no or negligible mark. Also, a good quality stone should absorb no or negligible amount of water when kept submersed in water.
Stone masonry may be classified in two primary categories: Rubble masonry and Ashlar masonry. While rubble masonry uses undressed or partially dressed stones, ashlar masonry uses fully dressed and uniformly shaped (like bricks) stones.
Rubble masonry is further subdivided into three classes: Uncoursed random rubble masonry, Coursed random rubble masonry and Dry rubble masonry. Similarly, ashlar masonry is further subdivided into four classes: Ashlar facing, Ashlar rock faced, Ashlar fine and Ashlar chamferred.
Like bricks, stones used in stone masonry too should be soaked in water before laying so that they don’t absorp any water from mortar. The stone should be so laid that loads act perpendicular to their natural beds or strata. Continuity of vertical joints must be avoided. The height of stones should preferably not exceed their widths. Joints should be pointed with rich mortar. Upon laying stone masonry should be cured for a fortnight or so.