General Types of Natural Stone-Sandstone
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2010-11-11 14:09:52
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The term sandstone is used to describe almost any stone of sedimentary origin with a granular texture. Some other types of stone that may fall under this classification include gritstones, siltstones, greywackes, conglomerates and marls. Aside from particle size variations, the dominant factor affecting sandstone performance is the grain cement that may be siliceous, calcareous, clay bearing or iron-rich.
Geologically it is a sedimentary type rock made up of various mineral particles mainly quartz, mica and felspar. All these minerals are bonded together with natural cements such as silicas, calcium carbonates, iron oxides and clays. The individual make up of each sandstone gives a wide range of colours. A pure silica sandstone is white with the colours arising from other minerals. Iron oxides can cause the stone to vary from buff or brown through to the deepest red. Grey colour stone is due to the presence of clay and green could indicate the presence of glauconite which contained potassium.
Sandstone is a natural material traditionally regarded as the building stone of the North. However, sandstone can be seen throughout the United Kingdom in many prestigious buildings from structures which form part of our heritage to modern office blocks. Sandstone is traditionally used as a building material in many areas where it occurs locally particularly in Derbyshire, Yorkshire and the North East of England, Wales and Scotland. Many of the “stone cities” of the North derive their particular architectural character from the use of sandstone. Most of the major sandstone quarries working today are located in the North of England, Derbyshire and Scotland. For flooring purposes, sandstones are also imported.
Appearance
Sandstone has many colours ranging from white, grey and buff to various shades of pink and red. The colour and texture of stone is self evident, however the colour of dry stone can change quite dramatically on wetting. Natural weathering can play a major part in the change of colour. Such colour change can sometimes be viewed on abandoned faces of the quarry although it is much more important to view existing buildings constructed from the same stone. Sandstones generally have an even texture, which may vary from course to fine, but the stone from some quarries also show attractive natural markings. Applications Many types of sandstone are suitable for paving or flooring. Some can be split (“riven”) otherwise the normal finish is sawn. Tooled, sandblasted and flame textured finishes are also available. There is a vast variety of surface finishes available from the traditional rubble walling to wrought stonework with its finishes to different forms ie. boasting, pitched, broached, hammer dressed and rusticated, to the very intricate looking vermiculated. But most importantly, credit must go to the craftsmen who hue the sandstone to all the various forms from large stones with a high degree of moulding to the most intricate of carving work. Sandstones are suitable for blcok construction in most building and engineering work and can now be cut to relatively thin sections for cladding to steel framed or concrete structured buildings. All in all sandstone is one of the few historic natural minerals still in use today. It provides excellent durability and is virtually maintenance free. It is aesthetically appealing to the eye whilst giving great value for money to the client. Performance Most sandstones have good load bearing and weathering properties. Correct detailling with regard to weathering is of prime importance, especially on buildings designed with sloping surfaces and without overhangs. Great care is required in the design of non-ferrous cramps and corbels for fixing to structures. |
