Termite soil as building material
Termite mounds are primarily made of soil, which is excavated below the mound and carried to the surface by these insects. They use the soil to construct the mound, forming it into a variety of shapes depending on the termite species. The exterior of the mound is usually coated with a hard, clay-like substance that helps to protect it from the elements and predators. Termites produce this substance by mixing soil with secretions from glands located on their bodies. And also use their saliva as a binding agent holding the substance together.
At another article in this section – see link here – we discussed the use of ‘ant hill’ material for construction purposes in Australia. And another article in the ‘Navigation’ section discusses general structures of termite mounds and reasons why the tips are often pointing towards North.
As in Southern Africa a variety of termite mound shapes and -soils were seen, I wanted to check randomly, if all termite mound soils are suitable as building material.
These tests were not done in a strict scientific way, as the number of samples was by far too low and no in-depth measurements were done. But the intention was to get with simple tests a first indication if all termite mound soils can be used as construction material- Either on its own or in a mix with cement or mortar – as implicated by a variety of scientific literature. Examples can be seen here or here and at many other publications.
Samples were taken from following locations:
Sample A: This sample was taken in Namibia, Otjozondjupa Region, eastern side next to B8 Road, 5 km north-east of Grootfontein. Active termite mound. Fist-sized sample taken from a freshly built-up termite mound tip. Color of the mound was reddish, but the sample turned out to be greyish when processing in Europe.
Sample B: South Africa, Mpumalanga Province, Three Rondavels, 100 m below the parking lot of the ‘Lowveld View’ near Leroro-A village. Inactive and on surface eroded termite mound. Fist-sized sample was taken from near the tip below the surface. Color of the mound was khaki, but the sample turned out to be a deep brownish-red when processing in Europe. There is no mix-up of samples A and B. The Color change of these two samples seems to be based on different humidity levels between South Africa and Austria.
Sample C: Namibia, Kunene Region, Etosha National Park, southern side next to C38 Road, 22 km west of Fort Namutoni. Inactive and broken-up termite mound. Fist-sized sample taken from the clay-coated outer surface in the lower region. Color of the sample when processing remained the same as the color of the mound was.
Back home in Austria, I processed the samples by first crushing them. Samples A and B could be easily broken down in a mortar. Sample C was so hard, that a heavy hammer had to be used crushing it.
Thereafter, samples A and B were mixed with water and put into round paper carton moulds for drying. From sample C only the fraction <5mm was used, as although sledging the sample heavily, very coarse grains remained. This fine fraction was again mixed with water and put into a paper carton mould.
After drying all three samples for three days at 25 degC until they were as dry as possible. Remaining humidity is not known, but all three samples appeared to be completely dry. In samples A and B there was a considerable change in colors of the samples compared to the color of the termite mounds they originated from.
Sample hardness characteristics
After de-moulding, it was attempted to break the re-hardened termite soil discs in the middle, as a kind of hardness test. Results were as follows:
Sample A: The structure was dense with no fine- but some big pores from trapped air. And the sample contained dry grass, which further acted as a reinforcement. Necessary force to break the disc was similar to breaking a thick piece of chocolate of similar dimensions. I was near my limit of power to break the disc in half.
Sample B: The structure appeared to be spongy and contained many fine pores throughout. Force necessary to break the disc was roughly half of that of sample A.
Sample C: There was nearly no gluing effect between the grains and the disc just crumbled away on handling. Basically, no force was needed to break the piece.
Sample behavior on water and application proposals
Behavior of Sample A
When putting sample A into a small puddle of water, the half-disc fully sucked up water within six minutes time and some of the material crumbled into fine grains. After water evaporation, the remaining disc and crumbled grains rehardened again. This material could be ideally used for hard-wearing surfaces indoors, like bottom floors of huts.
Behavior of Sample B
When putting sample B into a small puddle of water, the whole half-disc fully sucked up water within ten seconds time and more material – compared to sample A – crumbled into fine grains. After water evaporation, the remaining disc and crumbled grains rehardened again.
That means, this material is very prone to erosion by water and is therefore not suitable for building applications, which get in contact with water. But also, for indoor-use it only should be applied on non-hard-wearing surfaces due to its middle-high strength. It however could be used as plaster on walls keeping out insects. Especially if these plastered walls would be ‘papered’ – as the old colonists in Southern Africa called it.
Behavior of Sample C
When putting sample C into a small puddle of water, no water was visually absorbed. I therefore fully immersed a lump of sample C fully under water. After being immersed for 20 days, no visual deterioration of the lump could be seen. Just very few, single grains spalled off.
This kind of material is very hard wearing, not prone to erosion by water, but does not stick together on its own. It therefore could be used as as a replacement for rocks and gravel together with cement for creating concrete for hard-wearing surfaces outdoors, like stamping grounds in front of huts, grain silos, water tanks and similar applications.
These simple, indicative tests with three different samples showed it clearly. No termite soil is comparable to another termite soil from a different area. And even on the same termite mound, materials from the outside layer and from under this outside layer are behaving different. All materials are highly useable for the local population, either as building material itself or as an aggregate for mixing with cement or mortar. But before using it for building applications, above-described simple tests should be applied, if somebody has not got the local knowledge of a certain area. Locals will know through lore and traditions which part of termite mounds in the area can be used for which application.
When extracting termite soil from a mound, not more than one third of the mounds material content above the surface should be removed. Up to this limit, a healthy termite colony is able to close the gaps in relatively short time again to keep mound ventilation and protection against predators (mainly ants) functioning.
Lessons learned from termite soil as building material:
- Mineralogical content of termite mounds depends on the soil they are built on.
- Every single termite mound consists of inner material, outer material and outwash pediment material at the foot of the mound.
- Three different samples were taken, and every sample has got different characteristics for different building applications.
- When harvesting termite soil from a mound, not more than one third of material content above surface should be removed.