Lime Kilns

 JOURNAL 
 1994 
 North Craven 
 Heritage Trust 

Lime kilns, of various forms and in various states of repair, are a common landscape feature of the limestone areas of North Craven. The Yorkshire Dales Project, recently carried out by the Royal Commission on the Historical Monuments of England, records that over 880 were mapped in the area of the National Park in the 1850's. There were 90 in the North Craven area. The majority of these would have been field kilns, small isolated dry stone structures, sometimes free-standing but more often partly built into a hillside with a deep bowl at the top and a large, arched opening at the front. Within these kilns limestone, calcium carbonate, was burnt at about 900C to make quicklime, using locally mined coal or sometimes wood or peat as a fuel. Quicklime, calcium oxide, reacts violently with any material containing water and cannot be stored unless it is kept scrupulously dry. It did however have specific uses; dead animals were often buried with quicklime to prevent the spread of diseases while the violent reaction could be harnessed to split rock in mining and quarrying. More often however it was mixed with water, under controlled conditions, to form slaked lime, calcium hydroxide. Slaked lime was widely used in buildings and agriculture. Until this century it was the main ingredient of mortars, plasters and limewashes or renders. Agriculturally its main use was to sweeten or improve grassland by reducing the acidity of pastures especially of intake land or reclaimed moorland during the enclosures of the eighteenth or nineteenth centuries. Lime was also used in local industries, particularly as a flux in lead smelting and in tanning.

Most lime kilns are found closely associated with small limestone quarries or areas of limestone pavement but occasionally they can be found adjacent to transport routes. Many were built along canals, while the introduction of rail transport permitted the construction of large industrial kilns such as the now ruined Hoffman kilns at Meal Bank Quarry, Ingleton, and Langcliffe Quarry. Economies of scale led to the abandonment of most of the small lime kilns though a few, especially in the more isolated areas, continued in use until the early twentieth century.

Lime burning was a labour and fuel intensive process but the field kilns themselves represent a technology little changed from that of Roman times. The earliest kilns were essentially bonfire clamps: a piled up mixture of layers of limestone and fuel. Such kilns are known as pye or sow kilns, depending on their design, but were destroyed after every firing to retrieve the lime and have thus left very little in the way of remains, other than a slight circular or rectangular hollow surrounded by a low mound of un-burnt or partially burnt stone and waste. Few such kilns have so far been identified in the Yorkshire Dales in contrast to the large number of field kilns.

Field lime kilns represented a larger capital investment as it was necessary to build the kiln superstructure but they had the advantages of being reusable and of being more fuel efficient. Many were built and operated by farmers interested in improving their own land but some were operated on a commercial basis. A cross section of a typical field kiln is shown on the cover of this journal. Most field kilns were about 3 metres high and built of limestone although the circular bowl was usually lined with sandstone or firebricks which would not themselves be attacked during the burning process.

Kindling was laid in the bottom of the kiln and covered with layers of limestone, broken up into fistsized lumps, and coal. Much of the skill in lime burning lay in the careful filling of the bowl with the tipped layers of fuel and stone. About 48 hours after lighting, as the fire burnt through the fill in the bowl, burnt lime could be shovelled out through the draw arch at the bottom of the kiln while more unburnt limestone and coal could be tipped in at the top. Such kilns could work continuously but it is more likely that burning was intermittent.

There are several variations in the detailed appearance of field lime kilns. The most common forms are square or circular in plan but intermediate types are also found. Most have only one bowl and one draw arch. The draw arches are normally semicircular but some are pointed or have a series of stepped, recessed arches while on some smaller kilns, flat lintels were used instead of the arch. The dimensions also vary, larger kilns possibly being later or indicating a more commercial or selling function. The Yorkshire Dales National Park is encouraging individuals and groups to study the kilns of particular parishes and dales in an attempt to identify regional and local styles and to check if any can be dated by documentary means to see whether there are any variations over time. Many kiln sites however are almost unrecognisable as the bowls have been filled in to prevent sheep and other animals falling into them or have been covered by shrubs and trees.

These surveys are also recording the condition of lime kilns and identifying the best preserved examples. A proforma, available from the National Park, helps design features to be consistently recorded.

The National Park Authority is providing grants, through its Local Historic Features scheme, for the protection and consolidation of lime kilns, particularly those which are of historical or landscape importance. This scheme is intended to help landowners and others protect not just lime kilns but a wide range of small man made structures such as bee boles, boundary markers, pounds, pumps and washfolds. It offers grants of up to 100% of the costs of consolidation and maintenance of such features. A leaflet describing the scheme is available at National Park Centres and offices.

It is also hoped to identify one or more kilns which might be suitable for firing using traditional methods. Scientific monitoring of such lime burning experiments will enable us to better understand the efficiency and technology of lime burning. The end product will also provide a traditional basic building material for use in building conservation projects.

Lime is once again being used for building purposes because of its technical advantages in mortars, plasters and renders where it enables buildings to 'breathe'. The impurities of kiln burnt lime, fragments of burn stone or unburnt fuel, can also have a significant effect on the appearance and texture of building mortars and are thus important for authentic building conservation.

Anyone wishing to become involved in either of these projects or to find out more about the Yorkshire Dales Projects should contact the writer at the Bainbridge office of the National Park.

Robert White.

 

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Craven Lime Works, Stainforth. From "The Ancient Parish of Giggleswick", Settle Civic Society and Giggleswick School.



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J1994p1_9_files/tmp5A9-4.jpg
Craven Lime Works, Stainforth. From "The Ancient Parish of Giggleswick", Settle Civic Society and Giggleswick School.