Building with Earth: Design and Technology of a Sustainable Architecture

The disadvantage is that the blocks are
usually stabilised with a 4% to 8% cement
content in order to endow them with suffi-
cient strength. This is necessary because
of the absence of either sufficient water or
adequate dynamic impact capable of signifi-
cantly 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 com-
positions vary, then both the volume of the

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 .14and 6 .15can pro-
duce 1500 to 4000 blocks daily. However,
they require large investments and may be
difficult to maintain, especially in developing
countries. To assure even loam consisten-
cies, such machines often require separate
crushers and mixers.
Fully automatic presses are only economical
if they have long lives, are utilised extensive-
ly 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 dimin-

ish any potential economic advantages. In

low-wage countries, manual adobe produc-

tion 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 pre-

pared 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 extrud-

er, 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

64 Working with earthen blocks

6 .13CETA Ram, Paraguay

6 .14Automatic block

press CLU 3000, Switzer-

land

6 .15Automatic block

press (Pacific Adobe,

USA)

6 .16 t o 6 .17Adobe pro-

duction technique devel-

oped by Hans Stumpf,

USA

6 .18Green bricks drying

in the air at brick plant,

Gilserberg, Germany

6 .19Shrinkage cracks

that occurred after rain-

Special acoustic green bricks

dried out

Production of earth blocks

6 .14

6 .13

6 .15