| When one
thinks of stone, its use in famous buildings probably first comes
to mind, but few people probably realise that stone in some form
enters our lives probably a hundred times even before we leave the
house each day. Five main groups of uses can be identified:
- Building and decorative stone – stone used for its resistance
to weather or its aesthetic appeal – walls and decorative purposes.
Buildings, walls, paving slabs.
- Aggregates – stone used for its strong physical properties
– crushed and sorted into various sizes for use in concrete,
coated with bitumen to make asphalt or used 'dry' as bulk fill
in construction. Mostly used in roads, concrete and building
- Industrial purposes – limestone can be used for its chemical
(mainly alkaline) properties as calcium carbonate (CaCO3) in
farming and manufacturing industry.
- Lime burning (calcining) – limestone when heated to a high temperature
breaks down into lime (calcium oxide) and carbon dioxide gas.
It can then be used as a more powerful alkali than limestone
(see above) or used as a cement with sand, to make mortar, or
as a soil improver in agriculture.
- Cement – if limestone (or its variety chalk) is mixed with
clay or sandstone before firing, it can produce Portland cement
which when mixed with aggregate makes concrete.
Stone from Mendip quarries has been employed in all of these ways
(with the exception of Portland cement manufacture).
Until the 1920s, lime-burning, although small scale, was widespread.
The remains of hundreds of small lime-kilns can be seen scattered
across Mendip. Since the 1920s, lime burning has been concentrated
at larger plants. Throughout the middle of the 20th century, Callow
Rock and Gurney Slade quarries were the two main producers, by the
1970s both these had closed but a major new plant was established
at Batts Coombe. The main purpose of this investment was to supply
the South Wales steel industry at Llanwern and Port Talbot.
Aggregates represent about 98% of quarry output, most of which is
used in road construction, maintenance and repair. Much of this
goes to the production of asphalt, the remainder is used 'dry'
without the addition of other materials to provide a sturdy base
for roads. Some of the asphalt is processed in the area at or near
the quarry, the rest is processed at remote plants. Only the harder
more resilient rocks such as the Silurian andesite lavas from Moon's
Hill can be employed for most road surfacing requirements. The
harder Carboniferous Limestone aggregates are generally used in the lower
layers of roads and in footpaths, car parks etc. but polish too
readily (and hence have low resistance to skidding) to be used
for road surfacing.
Apart from road usage, substantial amounts are mixed (coarse gravel
sized stone with finer stone particles or sand) with cement and water
to make concrete. This may be carried out at the quarry or materials
supplied to truck-mixers (for mixing en route) or to remote plants.
An important local 'downstream' industry is that of concrete product
(blocks, pipes, kerbs, pavers, etc) with operations for example at
Callow Rock, Mells, Torr Works, Holcombe, Wells and Cheddar. Not
only do these produce 'added value' to the raw aggregate, they often
make use of 'fines' which are a by-product of general aggregate processing,
and without this market would often have to be dumped.
Non-aggregate and Industrial purposes
Only a very small amount (0.3–0.4 million tonnes annually) of Mendip
stone is destined for non-aggregate and industrial purposes. In most
instances, these are produced from those quarries, notably Batts
Coombe and Callow Rock working deposits of very pure calcium carbonate
limestones such as the Burrington Oolite. Uses include ground limestone
for soil conditioning in agriculture, animal feed supplements (e.g.
poultry grit) and latex treatment. Probably the largest single non-aggregate
application is limestone utilised as a flux in steel-making.
Today, the only building stone quarried on Mendip is Doulting Stone
(Jurassic Inferior Oolite). In the past, small quantities of other
materials have been worked as decorative stone and building stone,
but the total quantity produced in any year in the past has probably
never exceeded a few thousand tonnes and currently is only a few
The more important building stones are shown below:
||Draycott and surrounding areas
||Widespread local use
||Lower Lias Group
||North of Shepton Mallet
||Lower Lias Group
||Horrington and Chilcote area
||Doulting, Shepton Mallet
||Great Oolite Group
||Bath and Bradford on Avon