Improvement of water resistance and thermal comfort of earth renders by cow dung: an ancestral practice of Burkina Faso

The main objective of this study was to improve some properties (physical, mechanical, hydric and thermal) of earth renders amended by cow dung, as such amendment is an ancestral practice in Burkina Faso. For this purpose, raw clayey material from Kodeni (in western Burkina Faso), mainly composed of kaolinite (62 wt.%), quartz (31 wt.%) and goethite (2 wt.%) and having adequate geotechnical properties was used to elaborate earth renders reinforced with up to 6 wt.% of cow dung. The cow dung studied was mainly made up of small vegetable fibres, clayey minerals and quartz consumed by cows. Cow dung incorporation limits the spread of cracks and hardens the material thanks to the good adhesion of cow dung to the clayey matrix, which is linked to the rough surface of fibres contained in cow dung. The presence of cow dung in an earth render influences its mineralogy through the formation of insoluble amine silicate (Si(OH)4. 4NH3). This compound is formed during the reaction between fermented cow dung with mainly fine crushed quartz and feebly kaolinite in basic medium. The molecule formed links isolated raw material particles through free electronic doublets on the oxygen atoms and especially on the nitrogen atoms. The consequence of this effect is an improvement of the microstructural, physical and mechanical properties of earth renders. In particular, their thermal conductivity is reduced as the fibres present in the composite materials are rich in cellulose (molecule with thermally insulating properties), and their resistance to abrasion and to water is good. The earth renders elaborated in this way help to provide water resistant housing with good thermal comfort.