Herefordshire Through Time
Herefordshire Through Time
The Romans developed the process of burning limestone to make lime for use in building as the main ingredient in mortars, concretes, plasters, renders and washes. During the Middle Ages the demand for lime significantly increased as the construction of castles, city walls and religious buildings increased. However, up until the middle of the 18th century most limekilns in the country were temporary structures set up to burn the lime on-site. After they had served their purpose many were simply left to decay whilst others were dismantled to be re-built elsewhere.
Agricultural improvement also created an increase in demand for lime from the late 16th century onwards, as it was spread on fields to reduce the acidity of the soil and so increase the fertility. It also improved the structure of heavy and light soils (making them easier to work with) and helped to suppress weeds. Many of the farmers with larger landholdings had their own limekilns for this purpose. Lime was found to prevent blight in hops and was also useful in preventing clubroot in turnips, once the basic root crop grown in Herefordshire (Valerie Goodbury, Herefordshire Limekilns, University of Birmingham (Ironbridge Institute) dissertation,1992, pp. 5-6 (copy held in HER library)).
Lime was also used in the tanning process, which was once carried out throughout Herefordshire. Animal skins would be soaked in lime to remove the hair and enable the skin to absorb the tan more easily. There are also stories of lime being used in salmon poaching. It is said that lime was added to the river and it would cause an alteration in the oxygen levels in the water, which would make all the salmon rise to the surface. (Valerie Goodbury (see above), pp. 6-7)
The 18th century saw a further increase in demand as there was increased urban development as well as industrial and agricultural improvement on a large scale. The small-scale production of lime in rural areas continued into the 19th and 20th centuries.
Many farmers and kiln owners also advertised their services as limeburners. Presumably people could bring their limestone to the kiln, have it burnt and then take away the resulting lime. Kilns were also available for rent, but presumably this meant that you would have to do your own burning. It would appear that limeburners were considered to be skilled workers as they are listed separately from other agricultural workers in the early editions of the census. (Valerie Goodbury (see above), pp. 14-17)
The raw material needed for the production of lime is limestone or chalk and this can be extracted from a range of geological deposits. Limestones of varying quality and thickness occur in almost every county in England. In Herefordshire the Woolhope Dome to the south-east of Hereford is a good source of Woolhope, Aymestrey and Wenlock Limestone. Other areas of limestone quarrying are Leintwardine, Knill, Howle Hill, The Doward and Ledbury.
Limestone (calcium carbonate) was burnt in a kiln around 10-12ft in diameter and 3-4ft high, in alternate layers with the fuel. The whole thing would then be covered with slabs of turf and left to burn for anything up to a week, or even two. Originally wood was the fuel used in limekilns but c.1500 this was replaced by charcoal. It is said that for every two tons of limestone burnt, one ton of lime was produced.
This process of burning would release the carbon dioxide-producing quicklime (calcium oxide). Quicklime is chemically unstable in normal atmospheric conditions and combines with water to produce slaked lime (calcium hydroxide). The chemical reaction to turn quicklime into slaked lime releases heat and reduces the lumps of quicklime to a stable powder. When slaked lime or quicklime was added to the fields it would raise the pH of the soil and increase the fertility of the soil.
Slaked lime was also used as lime putty for building. This is soft when first mixed but it hardens as it takes in carbon dioxide (CO2) from the atmosphere and reverts to calcium limestone.
The use of burned limestone on the fields was later replaced with crushed limestone, and the local limekiln industry disappeared when production was concentrated into a small number of larger sites.
The simplest type of kiln is the clamp kiln, where firing takes place in a mound of mixed fuel and stone, sometimes in an excavated pit. Flare kilns are permanent masonry structures, fired intermittently (sometimes known as intermittent kilns). Within a rectangular or domed kiln superstructure, the top-loaded charge of stone is separated from a stoke pit or furnace below. Intermittent kilns used a lot of fuel as after they had been filled and fired they had to be allowed to cool completely before the lime was removed. However, Herefordshire had an abundance of the wood used to fire them and this was not such a concern.
The third type of kiln is the draw kiln, which is continually fired (also known as a continuous kiln). Like flare kilns they are permanent structures, often constructed against an artificial bank to enable top loading. This type of kiln contained one or more pots or charge holes (tapering chambers within which the burning of the fuel and limestone took place). At the base of the pot, draw holes or eyes allow a controllable airflow through the kiln and provide access to draw out the lime; there could be as many as four eyes per pot.
When firing a continuous kiln the fuel and lime had to be built up in particular layers. The first layer was of faggots or small pieces of wood, then there was a layer of coal and then a layer of limestone. The coal and limestone layers would be repeated to the top, where a final layer of coal was added. It could take up to two days to get the kiln firing correctly.
These are the commonest of the surviving historic kiln types. (Gill Chitty, Lime, Cement and Plaster Industries - Step 4 Report, English Heritage Monument Protection Programme, 2001 (copy held in HER library))
The limekilns began to suffer towards the end of the 19th century when more and more chemical fertilisers were being used on the fields. The localised burning of lime also declined during the two World Wars when more and more machinery was developed to do the job of the agricultural worker. There was a brief respite in 1937 when the Government, concerned at the falling fertility of the land, brought in the Land Fertility Scheme, which aimed to build up fertiliser supplies and encourage farmers to improve the condition of their land. As part of this scheme farmers could claim back half the cost of the lime delivered to the farm and this saw some of the small kilns put back into use.
In Herefordshire the typical kiln had a round top to the charge hole and was usually lined in stone, with the upper section sometimes in brick. It was a single kiln with two eyes, each with separate but adjoining tunnels. The eye would be in the centre of the rear wall and the arch was elliptical or rounded. The front wall (which incorporated the arches) is rectangular, made from rough coursed stone. Occasionally the arches and the vaulted roof may be of brick.
The Herefordshire Historic Environment Record database has records of 267 limekilns within the county, with good distribution over most of it but clear concentrations in the south-west, extreme south-east, north-east and just to the south-east of Hereford. Of these sites in Herefordshire in 1992, 70 were said to be standing remains with a further 37 recognisable as ruins or buried remains. The 1st Edition Ordnance Survey maps of the 1880s are a good place to look for limekilns, and they record over 130 limekilns in Herefordshire, both disused and still in use at the time of mapping.
[Original author: Miranda Greene, 2005]