WALLS OF EARTH

New Zealand Listener, Volume 15, Issue 386, 15 November 1946, Page 11

WALLS OF EARTH

(By

P. J.

ALLEY

senior lecturer in Civil

|p neneering, Canterbury University College) |

HE article in The Listener about a month or so ago on the subject of Earth Wall Construction was of great interest to me, because I had been doing some Soil Mechanics research at Canterbury College. ‘The article prompted me to analyse a sample of the walls of an old sod dairy on my mother’s property at Upper Riccarton. The walls of the dairy are in perfect condition and it was constructed about 1880. The sample was subjected to the various tests used in soil mechanics and was found to consist of the usual gradings of sand, clay, and silt that ordinary earthy material is composed of. But there was something else present. It consisted of a proportion of fibre, small pidces of grass, and an odd fragment of straw. At first I thought that this might be sawdust, but later | investigations showed it to be cow-dung. When a mixture of clay and water is made and the resulting soil cake allowed to dry in the sun or in an oven, and then the dry soil cake is placed on a grid immersed in water, the soil cake will begin to disintegrate or "slake." But this slaking does not occur when a mixture of clay and cow-dung is made. Using a proportion ‘of four parts of clay to one of cow-dung no slaking takes place. Herein, I suggest, lies the secret of why the walls of the earlier settlers’ houses have retained their shapes through all sorts of weather for a petiod of 60 years. Of course certain other materials such as cement can be used to mix in with certain types of clay to give the same effect.