Building with light earth

The LearnBIØN course #2 focused on lightweight constructions in earth building. While the first days were dedicated to explore an adjusted version of wattle-and-daub-techniques, in a second step the workshop-participants got the possibility to learn about lightweight, monolithic walls made of straw and raw earth.

This technique, known as light earth or light straw, consists in pressing straw in a cast after diving it in a bath of liquid earth. The wall is built with a sliding cast in layers of 45-50cm. After approximately 24 hours such a wall-piece can bear its weight and host the next layer. Full drying requires between 5 and 10 days.

As in any construction technique that involves natural resources, a good portion of attention had to be dedicated to assess the available raw material. Through several test molds it has been possible to determinate the optimal mix, which is light enough to act as insulating layer but strong enough to bear its own load and additional, accidental loads. The parameters to act on are the proportion of water to clay for the soaking mixture and the level of compactness that can be given to the straw mix. It is easy to understand that more compact parts have a higher specific weight.

On the building side, the straw-earth mix has been compacted manually with slight variations in density along the wall. This may cause some problem in the interpretation of performance data but won’t probably affect the overall behavior of the building.

The walls are 24 cm thick and have not been rendered in order to show the appealing straw texture in contrast with the smooth rendered surfaces of the quincha-panels.

During the realisation, the participants could also experience how easy it is to accommodate pipes and other devices for the installations in light straw constructions.