Building with earth - Gernot MINKE (1)

The disadvantage is that the blocks are
usually stabilised with a 4% to 8% cement
content in order to endow them with sufficient
strength. This is necessary because
of the absence of either sufficient water or
adequate dynamic impact capable of significantly
activating the binding forces of the
clay minerals. Without cement, pressed
blocks usually have dry a compressive
strength lower than that of handmade
adobes (see p. 44).
Another disadvantage of such presses is
that the soil mix must be kept at a constant
level of moisture and composition. If compositions
vary, then both the volume of the
6.13
6.15
material to be filled and the pressure
changes. This leads to variations in the
heights and strengths of the blocks.
Fully automatic block-making presses such
as those shown in 6.14 and 6.15 can produce
1500 to 4000 blocks daily. However,
they require large investments and may be
difficult to maintain, especially in developing
countries. To assure even loam consistencies,
such machines often require separate
crushers and mixers.
Fully automatic presses are only economical
if they have long lives, are utilised extensively
on a daily basis, and if raw material of
even consistency is available locally and
in sufficient quantities. Otherwise, capital,
maintenance and repair costs quickly diminish
any potential economic advantages. In
low-wage countries, manual adobe production
is usually more economical, as is the
production of green bricks in brick plants
in industrialised countries. In industrialised
countries, brick production using such
machines would be economical only if
transportation costs were high. (For more
information about pressed soil blocks, see
Mukerji, 1986; Smith and Webb, 1987;
Mukerji, 1988; and CRATerre, 1991).
The production method developed in the
USA by Hans Stumpf and patented in 1946,
and consisting of a block making apparatus,
seems comparatively more efficient (6.16
and 6.17). With this method, loam is prepared
to a pasty consistency in a forced
mixer and then poured into a large funnel
that moves over a grid of moulds. The
moulds are filled, and the top and the blocks
are then smoothed mechanically. A lever
lifts this grid, leaving the separated blocks
to dry on the ground. After a preliminary
drying period, the blocks can be turned on
their edges for even drying.
In mechanised brick plants, crushed soil is
mixed and pushed by rollers into an extruder,
where it is again mixed and pressed
through a vacuum-operated mouthpiece
into long profiles, which are then sliced by a
wire. Drying is accomplished in ovens using
commercial energy. Since this entire process
is computerised in industrialised brick plants,
it may be difficult to order green bricks, and
6.14
6.13 CETA Ram, Paraguay
6.14 Automatic block
press CLU 3000, Switzerland
6.15 Automatic block
press (Pacific Adobe,
USA)
6.16 to 6.17 Adobe production
technique developed
by Hans Stumpf,
USA
6.18 Green bricks drying
in the air at brick plant,
Gilserberg, Germany
6.19 Shrinkage cracks
that occurred after raindrenched
green bricks
dried out
6.20 Cutting earth blocks
64
Working with earthen blocks