Civil Engineering Reference
In-Depth Information
corners. After four to six weeks drying time the wall is strong enough to take the
roof. The roof is often put up provisionally before hand to protect the walls
against rain during the drying period. The earth loaf technique can of course be
used for internal walls, with or without a load-bearing function.
Extended earth tubes
This method has been recently developed by the Technical High School in Kassel,
Germany, and is a development of the earth loaf technique. In this case there is
not as much clay in the mix, as shrinkage would cause a problem, but the amount
of clay must be enough to give the mix a certain elasticity.
The earth is put in an extruding machine used for bricks (see Figure 8.7),
compressed, and then extruded in tubes of 8-16 cm in diameter. The capacity
of the machine is 1.5 m of tube per minute, and the length is unlimited. The
material is so well compressed from the beginning that it can be combined
and built without waiting for the lower layer to dry out. With a mobile
extruding machine a house can be built in a few days in the same way that a
vase of clay is made with long clay 'sausages'. Mortar is not necessary, but the
walls must be rendered afterwards. This technique is still at an early stage of
research.
The 'Sandbag' technique
Visually this building technique is similar to extruded earth tubes. The earth has
to be as free of clay as possible, i.e. pure sand, which has no binding properties.
The 'binder' is jute sacks which are 2.6 m long and about 0.5 wide. The sand-
filled sacks are piled up as walls within a light timber framework. The sand can
also be mixed with hydraulic lime mortar or cement, and the sacks dipped in
water before being piled up, so the mix becomes hard enough to make the sacks
superfluous. It is also possible to add some aggregate to increase the insulation
value.
The efficiency of earth building
Constructing a wall of earth needs about 2 per cent of the energy used to build a
similar wall in concrete. The building process for an earth wall is more labour-
than capital-intensive. The material is almost free, but the amount of labour is
very large. According to an investigation by the Norwegian Building Research
Institute in 1952 the following proportioning of labour was found (Bjerrum, 1952)
- the net time including only ramming and building up the wall, the gross time
including the surface treatment:
