Building with Earth: Design and Technology of a Sustainable Architecture

hence the shrinkage ratio. The results of this

method are shown in 4.2and 4.3. In 4.2, a

loam with 50% clay and 50% silt content

was mixed with increasing amounts of sand

until the shrinkage ratio approached zero.

To insure comparability, all samples tested

were of standard stiffness (see chapter 2,

p. 24). Interestingly, a shrinkage ratio of

0.1% is reached at a content of about 90%

sand measuring 0 to 2 mm diameter, while

the same ratio is reached earlier when using

sand having diameters of 0.25 to 1 mm, i.e.

at about 80%. A similar effect can be seen

in 4.3with silty loam, where the addition

of coarse sand (1 to 2 mm in diameter)

gives a better outcome than normal sand

with grains from 0 to 2 mm in diameter.

Illustration 4.4shows the influence of differ-

ent types of clay: one series thinned with

sand grains of 0 to 2 mm diameter with

90% to 95% pure Kaolinite, the other with

Bentonite, consisting of 71% Montmoril-

lonite and 16% Illite.

Thinning mediums

In the ceramic industry, fluid thinning

mediums are used to attain higher liquidity,

thereby allowing less water to be used

(in order to reduce shrinkage). Typical thin-

ning mediums are sodium waterglass

(Na 2 O · 3-4 SiO 2 ), Soda (Na 2 CO 3 ), and

humus acid and tannic acid. Tests conduct-

ed at the BRL at the University of Kassel

showed that these methods were of very

Earth as a building material: the essentials

al. But tests with whey were successful.

As a rule, it is only necessary to modify the

characteristics of loam for special applica-

tions. As we can see in 4.1, additives that

improve certain properties might worsen

others. For instance, compressive and bend-

ing strength can be raised by adding starch

and cellulose, but these additives also

reduce the binding force and increase the

shrinkage ratio, which is disadvantageous.

Reduction of shrinkage cracks

Because of increased erosion, shrinkage

cracks in loam surfaces exposed to rain

should be prevented. As described in chap-

ter 2 (p. 22), shrinkage during drying

depends on water content, on the kind and

amount of clay minerals present, and on the

grain size distribution of the aggregates.

Thinning

Addition of sand or larger aggregates to a

loam reduces the relative clay content and

39 Improving the earth

4 Improving the earth’s characteristics by special treatment

or additives

Without

Linseed oil 3%ISOFLOC 2%Cellulose 0.5 %

Cellulose 0.75 %Gelatine 0.5 %Starch 1 %Starch 2 %Whey 2 %Whey 4 %

Gelatine/Alum 0.5 %

Binding force

Tensile bending strengthCompressive strength

Shrinkage

Linear shrinkage (%)

Sand content (%)

Sand 0.25-1 Sand 0-2

Linear shrinkage (%)

Proportion Loam : Sand (by weight)

Sand 1-2

Sand 0-2

4.1

4.2 4.3

4.1Influence of various

additives on the shrink-

age, binding force, tensile

bending force and com-

pressive force of a sandy

loam

4.2Reduction of shrink-

age by adding sand to a

clayey loam

4.3Reduction of shrink-

age by adding sand to a

silty loam

5

4.5

4

3.5

3

2.5

2

1.5

1

0.5

0

2

1.8

1.6

1.4

1.2

1

0.8

0.6

0.4

0.2

0

1/2 1/3 1/4

0 20 40 60 80 100