Last updated  8.12.06

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Limekilns

Limekiln at St. Brides, Pembrokeshire, typically located by a small bay

Look at any old Ordnance Survey map of South Wales - particularly around the coast and the Vale - and you will see limekilns marked regularly all over the countryside. 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.

A pair of limekilns in Coed Nant-bran woods, north-west of St Lythans. The woods supplied the fuel and close by is a small quarry for the limestone.

There is evidence of lime being used for building as far back as 7000BC in Galilee and both the Egyptians and Romans used it extensively, the Romans mixing it with volcanic dust to produce a waterproof mortar to line aqueducts. Mortars for laying masonry were produced by mixing lime with sand and when mixed with an aggregate like crushed stone it made concrete. A mortar-like mix was used as plaster finally covered with a layer of neat lime. Mixing lime with water produced the traditional  whitewash for whitening walls.

Limekilns built into a depression so that the stone could be tipped in to the top more easily. This pair is north-west of Goldsland Wood near Dyffryn village.

With the ready availability of local limestone, there was extensive production of lime in South Wales for agriculture although much of it was exported to the West Country. 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.

This is not untypical of what you will often find. This limekiln near Michaelston-le-Pit is almost invisible through the summer, just beginning to appear as foliage dies back in Autumn.

The earliest limekilns were simple pit-like structures becoming more substantial stone and brick constructions from the mediaeval period onwards. 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 or they had a ramp constructed so that waggons could be hauled up and the material tipped down into the crucible.

Restored limekiln between Three Cliffs Bay and Oxwich on Gower at SS 52896/87985. Left, view looking towards Oxwich Point. Centre, one of two entrances. Right, hole above kiln where the limestone was tipped in.

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.

Left, ruined limekiln in Fforest Fawr not far from Castell Coch. Centre, limekiln at Oxwich on Gower. Right, Oxwich limekiln from the top showing the hole where the limestone was added.

The coastal limekilns, of which there are many in South Wales, could often be seen from the sea, becoming landmarks as they burned with a blue flame and giving off thick acrid yellow smoke. By 1900 most of the limekilns had stopped working as the railways proved more efficient for transporting lime than coastal shipping and as guano appeared as an abundant alternative source of fertilizer.

Limekilns close to the old harbour on Barry Island

The Aberthaw Limekiln

The substantial building in the photo is on the shoreline near East Aberthaw and is passed on the Coast walk. 

The Aberthaw Pebble Limekilns were opened on the 22nd December, 1888. The building consisted originally of two vertical potdraw kilns with a capacity of 300 tons each and with a total output of 40 tons of burnt lime per day. The main structure is of local limestone with firebricks lining the kilns. To the right of the building as you face it was a tramway ramp which allowed pebbles, measuring 3 - 4inches in diameter to be conveyed to the top of the building and then into the kilns. The burnt lime was conveyed to a Blake's stone-breaker which reduced the lime to walnut-sized pieces and this was followed by pulverisation by millstone to a fine powder which was then bagged.

Left, view from the interior. Right, the two kilns added later.

Two more pot kilns were added later to the north of the building. The central arched passageway was where the burnt lime was removed before crushing and the smaller archways led to a gallery surrounding each kiln.

Left, main arched front entrance. Right, interior passageway.

A tramway approached from the Rhoose direction and passed either side of the winch house which was situated just to the right of the building. Smeaton is reported to have used Aberthaw limestone in the construction of the Eddystone lighthouse but whilst he tested the limestone for suitability and found it effective, he actually used limestone from Watchet. The works closed in 1926 when the Aberthaw cement works started large-scale production of lime.

(For further information see 'The Aberthaw Pebble Limekilns' by Malcolm Brown published in Archive, No. 46, June 2005).

A working kiln

Re-created St Fagans lime kiln

There are not many working kilns around but in 2006 the National Museum at St Fagans re-created a mediaeval lime kiln which was based on the remains of a 13th century kiln at Cilgerran Castle, Pembrokeshire. The kiln is sited near the reconstruction of St Teilo's church, also 13th century but is not accessible to the general public. Contact the museum for information on visiting arrangements. The kiln has been used to produce lime in the traditional way and you can see the lime wash applied to the stone wall surrounding the church.