Building with earth - Gernot MINKE (1)

usual method using water is problematic,
shrinkage, the sandy mixture only 3%. After
since the sample dissolves at the joint.
three years of exposure to the weather, the
Therefore, the BRL modified the method by
clayey soil showed a special kind of scaling
closing the opening of the glass container
caused by frost. This was due to thin hairline
with filter paper (see 2.22, right). Results
cracks that appeared during drying, and
using this method were comparable to
through which rainwater was absorbed by
those using the method given in the Ger-
capillary action. When this water freezes, its
man standard DIN 52617 (see 2.23).
volume increases, causing the upper layers
Stability in static water
to burst. In areas where no hairline cracks
were found, this effect did not occur. Fur-
2.21
Stability in static water can be defined after
thermore, no rain erosion was observed in
the German standard DIN 18952 (Part 2),
these areas. The sample on the left does
as follows: a prismatic sample is immersed
not show this type of erosion after three
5 cm deep in water and the time it takes for
the submerged part to disintegrate is meas-
years. Here we see that some loam is
washed away by rain, so that the horizontal
Filter paper
ured. According to this standard, samples
that disintegrate in less than 45 minutes are
shrinkage crack is partially filled by these
particles, but no frost erosion is observable.
Silicon
Seal
unsuitable for earth construction. But this
test is unnecessary for earth construction
This is because there were no hairline
cracks, and because the loam contained
2.22
practices, since earth components would
pores large enough to allow the freezing
Water absorption w (kg/m 2 )
2.23
never be permanently immersed in water
in any case. Significant instead is resistance
to running water.
water to expand.
The test resulted in the following conclusions:
• sandy loam has little resistance against
1 Clayey loam, w – value
2 Clayey loam, Karsten
3 Silty loam, w – value
4 Silty loam, Karsten
Resistance to running water
rain, but is frost-resistant when free of
During construction, earth building elements
cracks;
are often exposed to rain and sensitive to
• loam with high clay content tends to
erosion, especially if still wet. It is important,
develop hairline cracks, and is therefore sus-
hence, to determine their resistance to run-
ceptible to frost. If there are no hairline
ning water. To compare the degrees of
cracks, it is almost rain-resistant.
Time t (min)
resistance of different loam mixtures, the
The higher the porosity and the larger the
BRL developed a test apparatus capable of
testing up to six samples simultaneously
(see 2.24). In this apparatus, water jets with
diameters of 4 mm are sprayed onto the
samples from a 45° angle and with a velocity
of 3.24 m/sec, simulating the worst
driving rain conditions in Europe.
pores, the higher loam’s resistance to frost.
Therefore, extruded common clay bricks
produced in a factory are not frost-resistant
and should not be used on outer exterior
walls in climates with frost. By contrast,
handmade adobes made from sandy loam
are usually frost-resistant.
2.21 Modified water
penetration test according
to BRL
2.22 Modified water
penetration test according
to BRL
2.23 Water absorption
according to Karsten and
the German standard
DIN 52617
Rain and frost erosion
Drying period
Illustration 2.25 shows two samples: each is
The period during which wet loam reaches
shown prior to testing (left), and after three
its equilibrium moisture content is called
years of weathering (right). The earth mix-
the “drying period.” The decreasing water
ture of the sample on the right contained
content and increasing shrinkage of a sandy
40% clay; the one on the left was mixed
mud mortar dried in a closed room at a
with sand, reducing the clay content to
temperature of 20°C and with a relative
16%. Both mixtures were tested with a mor-
humidity of ambient air of 81% and 44%
tar consistency in single layers 5 cm in thick-
respectively is shown in 2.26. With 44%
ness. After drying, large shrinkage cracks
humidity, the drying took about 14 days,
appeared. The clayey mixture showed 11%
while with 81% humidity, about 30. Illustra-
28
Properties of earth