Introduction to Sandstone

Most of us have images of sandstone in our minds. From the ancient temple and caves of Petra, Jordan carved from sandstone cliffs to the Red Fort in Delhi, India, and the historic tenement blocks of flats in Edinburgh and Glasgow, Scotland, sandstone makes for memorable architecture.

Sandstone’s natural strength and durability make it an ideal material for use in architecture. It can yield both clearly defined bedding along its sedimentary planes making it a great choice for traditional paving and walling products and also can yield enormous freestone capable of producing intricate and defined fine masonry. Its porosity like that of Limestone varies making it suitable for a host of horizontal and vertical construction applications.

Sandstone is a sedimentary rock made primarily of sand-sized mineral grains such as quartz, held together by naturally cementing minerals like Silica and Calcite. Its appearance can vary according to the mix of rock fragments and mineral composition. Quartz grains give a white, silver or grey colour, while black tones suggest the presence of coal. Clay minerals provide the browns and golden colours synonymous with blonde sandstone.

Blonde sandstone on Architextures

Sandstone forms when granules are weathered away from other types of rock and are subject to a sequence of weathering and erosion known as denudation. Physical weathering from ice, water flow, waves, rain, wind or thermal activity strips or grinds down parts of the origin rock, with particles being transported, or eroded, away from the source area by glaciers, rivers, wind or water, to be deposited in one area such as rivers, lakes or deserts. The transportation process helps destroy granules of weaker minerals, while rounding and smoothing the stronger minerals, typically quartz. The higher the quartz content of sandstone, the more mature and robust it is considered.

The deposited particles undergo lithification, a geological process that transforms loose sediments into solid rock over an extensive period of time. Particles are compacted in layers, compressed under their own weight and bound or cemented together when exposed to and combined with chemicals such as silica and calcium carbonate or, in the case of red sandstone, higher concentrations of iron oxide. This process helps to increase the bond between the granules and reduce the porosity of the newly formed rock.

Stone suppliers Albion Stone PLC and Hutton Stone Co. – both members of The Stone Collective– are pioneering the production and use of stone bricks. © Ivan Jones

Sandstone surfaces are commonly smooth in appearance and profile with some swirling, veined lines and linear colour patterns present, likely caused by water while the sandstone formed in river or ocean basins. The fine, consistent grain of sandstone makes it popular with masons as these characteristics lend themselves to carving decorative, ornamental pieces. Sandstone can adopt a variety of finishes, including natural hand cut, honed, brushed, and polished. The sandstone sometimes reveals its origins through shell fragments from marine environments to fossils formed by leaf impressions in terrestrial sandstone.

Its hardiness, durability and compressive strength allow sandstone to be used for load bearing structures, while remaining relatively soft enough to cut effectively to be carved into blocks, bricks, panels, or other shapes.

New applications of sandstone include low carbon stone bricks that have a fraction of the embodied carbon compared to their clay fired cousins. A new generation of architects are embracing the variety and versatility of natural stone and realising that this ancient material has much to offer.