Limekilns have been used for many centuries to convert limestone into lime. Lime had three principal uses. It was spread on the fields to improve the fertility of the soil. It was used as a mortar in the construction of buildings. It was also used as a limewash - the original whitewash applied to the outside walls of buildings.
With the ready availability of local limestone, there was extensive production of lime in South Wales for agriculture. It was used on heavy soils to make them more open and friable and combined with organic matter to produce plant nutrients particularly on acidic soils.
Limekilns in Wales were mostly circular although some were square. At the bottom of the kiln were arched openings used to feed the fire and allow oxygen to enter and from which the processed lime could be extracted. Charcoal, coal or wood was used as a fuel. A fire was lit at the base and then alternate layers of limestone and fuel were introduced from the top. For this reason they were often built into hillsides or the sides of natural depressions so that waggons could tip the material down into the crucible.
Once the temperature had reached about 900 centigrade, the limestone or Calcium Carbonate would lose Carbon Dioxide to become Calcium Oxide or quicklime. Quicklime is highly volatile and ships transporting it not infrequently caught fire if the quicklime came into contact with water. In its raw state it would kill anything growing so farmers would leave piles of it in the corners of fields to take in water naturally. This process was known as 'slaking' and the 'slaked lime' or Calcium Hydroxide could then be spread over the fields, usually at a rate of around 4 tons per acre.