Lime kilns at Kalkheuwel

Neither the Stone Age nor the Iron Age people made use of lime. But white pioneers came to these regions with the tradition of using lime as binding material in building mortar and plaster or for the lime washing of plastered walls. It was and is still also used in agriculture to regulate the pH value of soils and in the process of discarding infected animal carcasses. It was also used on a small scale in fireworks and stage lighting in the form of bright white “lime light”.

In nature we find lime in the form of CaCo3 (calcium carbonate or limestone). Dolomite, of which the mountains to the south of the Witwatersberg are composed, is mainly limestone.

When limestone is fired with wood or charcoal fires at a temperature of 1200-1400 degrees C, it turns into CaO3 (calcium oxide or burnt/unslaked lime, also called “quicklime” for its corrosive action). This is a blue-white powder which reacts with water to form Ca(HO)3 (calcium hydrate, called hydrated or slaked lime). This process releases intensive heat.

The slaked lime is mixed with sand and water and used as building mortar. Over time the calcium hydrate reacts with carbon dioxide in the air and turns into calcium carbonate again which is a hard crystalline material that binds the sand grains together. To hasten the hardening process the mixed heap of mortal was kept wet and turned for some days to expose it to carbon dioxide. Sometimes fires were made in and around newly built houses. The same process takes place in lime wash, only that no sand is used, but pigments of coloured ground or clay were used in the older times.

After the discovery of gold, the ZAR (Zuid-Afrikaansche Republiek) went into a period of rapid development with a building boom that used a lot of lime. With its convenient nearby position, Kalkheuwel (Afrikaans word for “Lime Hill”) was then extensively mined for lime. The dolomite was excavated and burnt in the numerous limekilns that were operated on Kalkheuwel. These were 3m diameter and 6m to 9m cylinders built of brick into embankments so as to make easy to feed the wood and limestone from the top and to remove the burnt lime at the bottom. When cement was made in South Africa in the beginning of the twentieth century lime was no longer commonly used. The limekilns at Kalkheuwel were left behind and today stand there as monuments and reminders of yesteryears’ activities. The dolomite also contains millions of fossil bones of animals and humans that lived in the area more than two million years ago. The first of these fossils was discovered at a working limekiln. In 2001 the whole area around and including Kalkheuwel was declared a World Heritage Site so that dolomite mining is forbidden. Now the limekilns are the “to be protected” heritage relicts.

Two or more lime kilns were often built next to each other where a suitable embankment was available.
The old lime kilns are impressive monuments.
One of the old lime kilns seen from above. Note the marks left by the fires.