Reasons for Designation
Limestone or chalk has been the basic ingredient for lime mortar from at
least Roman times. Since the medieval period, lime has also been used as
agricultural fertiliser and, since the early 19th century, widely used in
a variety of other industries: as a flux in blast furnaces, in the
production of gas and oil, and in the chemical, pharmaceutical and food
industries.
The lime industry is defined as the processes of preparing and producing
lime by burning and slaking. The basic raw material for producing lime is
limestone or chalk: when burnt at high temperature (roasted or calcined),
these rocks release carbon dioxide, leaving `quicklime' which, by chemical
reaction when mixed with water (`slaking'), can be turned into a stable
powder - lime. Lime burning sites varied in scale from individual small
lime kilns adjacent to a quarry, to large-scale works designed to operate
commercially for an extended market and often associated with long
distance water or rail transport. Lime burning as an industry displays
well-developed regional characteristics, borne out by the regional styles
of East Anglia, West Gloucestershire or Derbyshire.
The form of kilns used for lime burning evolved throughout the history of
the industry, from small intermittent clamp and flare kilns, to large
continuously fired draw kilns that could satisfy increased demand from
urban development, industrial growth and agricultural improvement.
Small-scale rural lime production continued in the later 19th and 20th
centuries, but this period of the industry is mainly characterised by
large-scale production and the transfer of technologies from the cement
and other industries. The demand for mortars grew steadily during the 19th
and 20th centuries. The successful production of mortars made with
artificial cement represented an economic challenge to lime production and
gradually replaced the use of lime mortars in major construction and
engineering projects.
From a highly selective sample made at national level, around 200 lime
industry sites have been defined as being of national importance. These
have been defined to represent the industry's chronological depth,
technological breadth and regional diversity.
The Bohetherick lime kiln survives very well with little modification since
its abandonment. Its overall design is typical of most Cornish lime kilns of
this period but it also contains several unusual features, notably the upper
vents to the pots and the clear evidence for phasing in its construction. The
close proximity of the kiln with the quay and its ancillary buildings provides
a good example of the structural grouping associated with lime burning of this
period, an aspect further enhanced by the several surviving 19th century
illustrations depicting this kiln while in use. The presence of the surviving
lime kilns at Cotehele Quay demonstrates well the wider context, with kilns
densely distributed behind most mooring points along the estuary.
Details
The scheduling includes the Bohetherick lime kiln with the adjacent access
trackway and quay, situated on the west bank of the River Tamar at its
confluence with the Morden stream. The quay contains three built
structures ancillary to the lime kiln. The lime kiln is a Listed Building
Grade II.
The Bohetherick lime kiln was constructed during the late 18th to early
19th centuries to provide slaked lime for both building and agricultural
uses. It contains a row of three conical pots designed to operate
continuously, the central pot flanked by two others of later phases. The
fabric of the structure is of random slate rubble. The kiln is built on a
bedrock plinth into which its features are cut to a depth of 1.1m at the
western end. A string course defines the upper third of the kiln's central
portion and the draw-arch to its east; the absence of the string course at
each end suggests phases in the kiln's construction reflecting
modification and repair throughout its working life. Details of the kiln's
fabric and form suggest a construction sequence with the larger central
pot built first, followed by those at the eastern and western ends
respectively.
The pots are in the form of inverted cones, the normal design in Cornwall
in the 18th and 19th centuries. Each pot is accessed by a draw-arch; one
to each side in the kiln's central section serves a central pot and the
pot on that side. The eastern pot is served by an additional draw-arch on
the east of the kiln. The wall dividing the base of each pot from the
draw-arch is pierced by a rectangular draw-hole, through which the burnt
lime was extracted, with a smaller poke-hole above to dislodge any
encrusted deposits. The eastern and western pots are also provided with
higher-level vents in tall, narrow openings in the kiln's outer face.
Towards the River Tamar and the Morden stream the kiln fronts a roughly
levelled quayside area shown with a revetted edge on the 1842 Tithe Map. A
painting by George Cole dated 1872 shows a sailing vessel berthed
alongside the quay. Remains of two small ancillary buildings and a loading
wharf survive on the quay surface in positions matching those of
structures also shown on the 1842 Tithe Map. The footings of one building
protrude from the Tamar riverbank to the east of the kiln, appearing as a
rubble-built wall corner from a structure with a slate-paved interior,
extending beneath the uneven land between the kiln and the water's edge.
The second building appears as low walling of a rectangular structure
levelled into the steeply sloping southern bank of the Morden stream north
west of the lime kiln. The third structure is a walled loading wharf to
the SSE of the lime kiln on the bank of the River Tamar. The quay and the
lime kiln were accessed by tracks leading down from the road above on the
west and south. A sloping track, called a charging ramp, also rises from
the quay to the eastern side of the lime kiln's rear side.
This kiln lies within the parish of St Dominick, which has the longest
recorded tradition of lime burning in the Tamar Valley with a kiln in
operation nearby at Halton by 1411. The increased exploitation of burnt
lime for agricultural use from the mid-18th century led to the
construction of lime kilns on most of southern Cornwall's coastal sites
and estuaries accessible to small cargo vessels. The Tamar estuary is
particularly rich in kilns of this period including two groups of
surviving 19th century kilns behind Cotehele Quay, lying some 120m north
of this scheduling.
The surface of the modern metalled road and all modern fencing are
excluded from the scheduling, although the ground beneath them is
included.
MAP EXTRACT
The site of the monument is shown on the attached map extract.
It includes a 2 metre boundary around the archaeological features,
considered to be essential for the monument's support and preservation.
