Building with Earth: Design and Technology of a Sustainable Architecture

a machine (3.8). This has steel angles fixed

onto a horizontal plate, which rotates at a

rate of 1440 rotations per minute. It requires

an electric engine of 4 kW. The machine

does not work if the lumps are wet. Another

example can be seen in 3.9, manufactured

by Ceratec, Belgium, which is able to crush

up to 20 m^3 of clods in eight hours with

a 3-horse-power engine. In this machine,

the clods are crushed by two counter-rotat-

ing cylinders. The machine shown in 3 .10,

manufactured by the firm Royer in France,

can crush up to 30 m^3 of earth clods in

eight hours.

It is always important to get the ready-

mixed material out of the container fairly

soon. There are different possibilities for

doing so: the machine shown in 3.5has an

opening at the bottom through which the

mixture can be pushed automatically into

a wheelbarrow, and the container of the

apparatus can be tilted so that it falls into

the flat wheelbarrow below.

Common concrete mixers where only the

drum rotates are unsuitable for preparing

loam mixtures, because in them, the clods

of earth agglomerate instead of breaking

down.

An electric hand mixer of the kind shown in

3.7is very time-consuming and is recom-

mended only if small quantities of mud

mortar or plaster are to be prepared.

Sieving

For specific earth construction techniques, it

might be necessary to sieve out larger parti-

cles. The simplest method that can be used

is to throw the dry material over a sieve.

More effective is an apparatus with a cylin-

drical sieve that is inclined and turned by

hand or engine (3 .11).

Mechanical slurrying

In order to enrich a sandy soil with clay or

prepare a lightweight loam, slurry is usually

required. This can be prepared most easily

from dry loam powder mixed with water.

If clods of clayey soil are to be used, they

have to remain covered with water for

some days in large flat containers. After

that, slurry can be obtained by using special

rakes, as shown in 3 .12, or by using electrical

hand mixers, as shown in 3 .10. A forced

mixer usually used for mixing and spraying

plaster is more efficient.

Water curing

Water curing is a process by which the wet

loam mixture is allowed to stand for a peri-

od of 12 to 48 hours. Experience shows that

this process enhances the binding force of

the loam. This phenomenon is probably due

to electrochemical attraction between differ-

ent clay minerals that forces them into a

more compact and ordered pattern.

Thinning

If it is too rich in clay, loam must be made

lean. Coarse aggregates like sand or gravel

are added, increasing the compressive

strength of the loam. The coarse aggregates

should always be moistened before being

mixed into the rich loam. Besides sand and

pebbles, hair, cow dung, heather, straw,

husk, sawdust and other similar materials

can also be used. These also serve to

reduce the shrinkage; some even serve to

increase the degree of thermal insulation.

38 Moisture protection

3.9 Crusher (Ceratec)
3 .10Crusher (Royer)
3 .11Sieving device
3 .12Rakes for pre-
paring loam slurries

3.9

3 .10

3 .11

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