The Technique of the Tri-Layer Coating: An Effective Solution for the Protection of Earthen Constructions

The problem with earth constructions is their low resistance to water. Step by step, the water degrades the exterior facings of the structures and ends up creating zones of weakness through the structures, making them collapse and creating enormous socio-economic problems, especially in rural areas. The solutions proposed to date, like the use of straw, cow dung, boiled skins, banana leaves, tar, cement soil, have shown their limits. Generally, the poor adhesion between the protected material and the protective layer means that the latter always ends up peeling off. This work, which is inspired by the traditional practice where plant tannins are used to brush the earthen walls to waterproof them, proposes a tri-layer coating composed of soil, powder and hydrolysable tannins extracted from the stem bark of Bridelia. This work focuses on the geotechnical characterization of the soil, the extraction of hydrolysable tannin, the manufacture of the micro-coating, the resistance tests carried out on the micro-coating, the technique of implementation and the test of evaluation of the performance of the tri-layer coating. The results obtained show that not only does the tri-layer coating adhere perfectly to the layer to protect, but it also waterproofs it and protects it against shocks.