Lime kilns are structures, which were formerly used
to manufacture lime (calcium oxide) by burning calcium carbonate at
temperatures of more than 900°C. The calcium carbonate that was burned (or
calcined) was usually limestone or chalk. Lime is also known as quicklime,
unslaked lime, burnt lime or lump lime.
The majority of
the quicklime that was produced was mixed with water to produce hydrated lime or
slaked lime (calcium hydroxide). Calcium
oxide is chemically unstable in normal atmospheric conditions but the chemical
reaction, which turns calcium oxide into calcium hydroxide releases heat and results
in a stable white powder. This was a key ingredient in plasters, renders, mortar
and concrete. It was also used in lime-wash to waterproof walls and lighten the
interiors of buildings; to bleach paper; by tanners to prepare animal hides for
tanning and as a disinfectant in medicine.
The production
of lime was introduced to Britain by the Romans. Demand for lime increased in
the medieval period when more buildings were built from stone and large
quantities of lime were needed for mortar, which was used in the construction
of castles, city walls and religious buildings.
In parts of Britain lime was also used to neutralise acidic soils to
improve their fertility and to improve the structure of heavy clay soils from
the late medieval period onwards.
There were three
types of lime kilns:
- Clamp kilns. This was the earliest design of kiln to
be used. Layers of coal or wood and limestone were stacked together in a
mound. This was then covered with clay
or turf and slowly burned in a method similar to that used in charcoal burning.
- Flare kilns. These were also known as intermittent or periodic kilns. This type of
kiln was used in the Roman and medieval periods. The limestone was stacked on top of the fuel
but separated from it by stone blocks, so that the lime was not contaminated
with ash. After burning for several days, the kiln had to be cooled down
completely before the lime could be removed and the kiln could be re-loaded for
the next firing.
- Draw kilns.
These were also called perpetual or running kilns and they were in use
more recently than flare kilns. This type of kiln was kept burning
continuously. There was a permanent grate
above the hearth. Fuel and limestone
were stack in alternate layers above the grate.
The calcined limestone dropped down through the grate and could be raked
out, while new layers were added at the top of the kiln.
Flare and draw
kilns had the same basic structure, consisting of a wide stone chamber with a
hearth at the base and one or two drawholes, stoke holes, eyes or flues at the
base.
Until the mid-18th
century most lime kilns were built to produce lime used in the construction of
buildings and they were therefore located a short distance from those buildings but away
from inhabited areas, as they produced noxious fumes and smoke. Lime kilns were
usually located in sheltered locations close to a source of limestone or chalk
and where sufficient firewood was also available. They are also often found in coastal locations
where limestone/chalk and/or coal could be delivered by sea.
Sometimes a single kiln was built but it is not usual for there to be
two or more in the same location. Some
kilns were built into banks of rising ground.
By the end of
the 19th century industrial kilns were mass producing lime at lower
prices and an improved transport network allowed the lime produced to be distributed
across the country.
Some of the lime kilns still standing today in Britain date from the 16th and 17th centuries but most are from the 18th and 19th centuries. They are a relatively common sight in Somerset.
Lime kiln south of Rich's Holford
Porlock Weir
Porlock Weir
Bishopswood Meadows
Information board at Bishopswood Meadows Lime Kiln
On the coast to the west of Watchet
This complex of three lime kilns was leased from the Luttrell Estate by the Gooding family from 1863 until c1913. They also operated a small industrial complex at Colling's Mill, Washford where they produced artificial manure, plaster of Paris and hydraulic cement. Local lias limestone was burned using coal imported from Wales.
Wiseburrow Farm, Greenham
Wiseburrow Farm, Greenham
Langford Heathfield
On the coast at East Quantoxhead
Staple Fitzpaine
Daws Castle, Watchet
Whitley Brake, South of Bilbrook
Kilve
Quarry Road, Sandford Batch
Plaque on the Sandford Batch lime kilns
South Landing, Steep Holm
Near Fitzhead
Black Rock Drove
This lime kiln at Black Rock Drove in the Mendip Hills was built in 1936 but became disused when the adjacent quarry, which had only opened in 1930, was sold and closed down in around 1940.
Lime kiln close to Doniford Beach
Lime kiln in Thurlbear Wood
