Sandstones
The term ‘sandstone’, when used to describe a range of natural materials suitable for paving
projects, covers a number of different types of stone, each with their own properties. Until the
late 1980s, sandstone was the common name for stones from Yorkshire and Lancashire, where
minerals peculiar to those areas created stone that was famed since Medieval times, quarried
and worked into building blocks and pavement products on thousands of streets and buildings.
Made up of quartz, mica, iron oxides and feldspar, with a range of colours from sandy yellow,
grey, brown and shades of tan, York stones hues tend to be more varied, with some of the
Lancastrian quarries producing stone that is almost monocolour, with a medium grained
Millstone grit texture.
Yorkstone is available in natural riven (split and rived from the layers or beds within the
formation) or sawn, usually six sides, to a range of thicknesses and dimensions. Mainly sawn
using diamond blades to create a smooth finish, it is also available as ‘shot sawn’(sawn using
lead shot and water) and ‘flame textured’ or ‘shot finished’ to provide an attractive non-slip
appearance, with flame textured often used in street/pedestrian areas of high foot traffic.
‘Plates’ of naturally riven Yorkstone are sometimes used as crazy paving, using broken pieces
formed into kaleidoscopic patterns, usually pointed with sand and cement, but also set into
concrete and ‘jointed’ using low growing alpines to provide a ‘soft’ patio or seating area (see
Soil Concrete) in between the plates instead of pointing.
Depending on the quarry – Halifax being one of the most famous sites – the material that was
produced by the owners was known for its very high crushing strength, low porosity and high
density, with a compressive strength (MPa) of 121, Flexural strength of 11.0 and density (kg/
m3) of 2406, makes York stone (or Yorkstone) one of the finest and long-lasting of paving
materials, famed for its extraordinary durability and slip resistance.
Since the 1980s, when sandstone was first introduced into the UK from quarries in India, a very
wide range of different coloured slabs appeared where they were championed by designers,
being their choice of paving material, due to regular sizes and low prices. Even when sourced
from the other side of the world, the packaging, transport and volume of availability of the ‘new’
sandstones rapidly made them the most popular and least expensive in the domestic market.
In the ‘early days’, Indian stone was riven to a thickness of 30mm, which made them very
rigid and strong in the main. Some of the first to arrive were Kotah and Kandla, both dense
sandstones, followed by others, some of lesser quality, being more porous and thinner and
thinner, now being passed through a ‘thicknesser’ to create slabs of 20mm thick, to save on
transport costs and enable even lower prices. The thicker slabs could be laid into a bed of
strong, wet mortar over a solid base, and pointed using sand and cement.
Today, Indian sandstones should be laid over a solid base of either MOT Type 1 with a full
contact mortar bed and a full coat of bonding mortar applied to their backs to secure them
into position, or laid over a bed of concrete (again, with fully bonded backs, to prevent them
from coming loose from their positions. Always ensure the backs of the slabs are brushed and
cleaned to remove any calibration dust before applying the bonding mortar.
