Building with earth - Gernot MINKE (1)

albuminate (which is not water-soluble). The
cellulose in the urine and manure enhances
the binding force, as the cellulose fibres act
as reinforcement. The ammoniac compounds
act as a disinfectant against microorganisms.
Two other recipes successfully
tested at the BRL are: (a) one part hydraulic
lime, four parts wet cow dung, three days
old, and eight parts sandy loam, and (b)
four parts hydrated lime, one part fat-free
white cheese, and ten parts sandy loam.
Plant products
Plant juices containing oily and latex and
derived from plants such as sisal, agave,
bananas and Euphorbia herea, usually in
combination with lime, are used as a stabilising
coating with success in many countries.
Investigations at the BRL showed that
a high degree of weather protection could
be obtained for loam surfaces using doubleboiled
linseed oil. It must be mentioned,
however, that vapour diffusion is heavily
reduced in these cases (see chapter 2,
p. 29). Several reports show that cooked
starch and molasses can also be used to
enhance stability. This effect is more pronounced
if a little lime is also added.
Artificial stabilisers
Synthetic resins, paraffins, synthetic waxes
and synthetic latex are all known to have a
stabilising effect on loam. However, because
they are relatively expensive, prone to ultraviolet
degradation, and because they act as
vapour barriers, they are not discussed in
greater detail in this book. These stabilisers
should be tested before use.
Silane, siloxane, silicones, silica ester and
acrylates all have water-repellent effects.
They are discussed in greater detail in chapter
12, p. 101.
Enhancement of binding force
4.7
But if the binding force is insufficient, it can
be increased by adding clay or by better
preparation, that is, by kneading and water
curing (see chapter 3, p. 38). Mineral, animal
and plant products that are usually added
to enhance the weather resistance of loam
also normally enhance its binding force,
although they may sometimes reduce it.
This section explains the various methods
by which binding force can be increased.
Mixing and water curing
It is interesting to note that depending upon
their method of preparation, different loam
samples from the same mix can have different
binding forces. If there is enough water
for preparation, then kneading, stirring and
curing enhance binding force.
At the BRL, it was discovered that after
being mixed for ten minutes in a laboratory
mixer, a silty mud mortar acquired a binding
force that was 57% higher than the same
mixture when mixed for only one minute.
Nevertheless, there was an 11% reduction
in the binding force after 20 minutes, which
suggests the existence of an optimum mixing
time. The increase in binding force due
to a longer preparation time is demonstrated
by a simple test. Illustration 4.7 shows
two earth balls 5 cm in diameter dropped
from a height of 2 m onto a hard surface.
Both were prepared to the same consistency,
as determined by the plastic limit. The
ball on the left was mixed for two minutes,
the one on the right for ten minutes. A
comparison shows that the sample that
was mixed longer demonstrates much less
deformation and tended to crack less.
4.7 Ball dropping test
to demonstrate different
binding forces
4.8 Modified ‘Fuller-
Parabola’ (Boemans,
1989)
The way in which binding force is derived
has already been described in chapter 2,
p. 32. Normally, no specific binding force is
needed with loam as a building material.
Increasing clay content
A simple method for enhancing the binding
force of very lean earth mixes is to add soil
with a high clay content or even pure clay.
42
Improving the earth