Building with earth - Gernot MINKE (1)

New wall construction techniques
Rammed earth panels
In order to prevent horizontal shrinkage
cracks at the vertical joints in traditional
rammed earth construction, a new technique
was developed at the BRL for producing
one-storey-height panels, with widths
of up to 2.4 m, in a continuous ramming
process. This technique avoids horizontal
joints, and the vertical joints that occur are
closed only after the shrinkage is complete.
For lateral stability, the vertical joints are
made in a tongue-in-groove pattern. No
shrinkage cracks occur within the panels for
these sizes. The reduction of length due to
shrinkage is only visible at the joint. (The
joint acts like a pre-designed contraction
joint). In order to avoid a formwork that
would have to be an entire storey in height,
a slip form was developed at the BRL. Illustration
5.19 shows the design in steel, while
5.17 and 5.18 show a later design in wood
(which proved easier to work with).
The formwork is spaced at the bottom with
only a steel bar, which leaves a very small
hole after dismantling. The top space is
positioned above the top level of the wall
and does not interfere with the process. As
the figures show, it is possible to use either
a simpler solution with a timber spacer on
top fixed to the vertical members, thus
forming a yoke, or a more sophisticated
version made from steel, which also allows
fine adjustments of distance at the top.
The first building using this technique was
built at the University of Kassel in 1982
(5.21). The soil contained about 10% clay
and about 50% sand. The earth was
rammed by the vibrator described on p. 55
and shown in 5.12 and 5.13. The linear
shrinkage of these elements was only 0.4%.
After drying, the joints were filled with a
loam stabilised with 8%double-boiled
linseed oil. A roof overhang of 60 cm and
a plinth of 50 cm were sufficient to ensure
that the wall did not erode and that it
required no surface treatment.
Highly mechanised techniques
The firm Rammed Earth Works has built
several rammed earth houses in California
utilising a special formwork made of thick
plywood, as shown in 5.20. Earth was filled
into the forms by a dumper and compacted
by a pneumatic ram. By this means, the
labour input could be as low as 2 h/m 3 .
In Australia, several firms are also using this
type of highly mechanised construction
process (5.22 and 5.23). In recent decades,
more than a hundred rammed earth buildings
have been constructed on the Australian
continent (Oliver, 1985). Illustration
5.24 shows a church in Margaret River
designed by Hodge and Wilson and built
by the firm Ramtec. As seen in 5.25, even
the columns supporting the roof structure
are made from rammed earth.
In 1992, the Kooralbyn Valley Resort Hotel
was built in Australia (architects: I. Hannaford,
F. Raadschelders, D. Oliver), where all
walls are made of unplastered rammed
earth (5.27 and 5.28).
5.17 to 5.19 Sliding
formwork for rammed
earth panels (BRL)
5.20 Formwork
(Rammed Earth Works,
USA)
5.21 Test building,
University of Kassel,
Germany, 1982
5.22 to 5.23 Mechanised
rammed earthwork
in progress
(Terrastone)
5.17
56
Rammed earthworks
5.18