Civil Engineering Reference
In-Depth Information
4. The mixture is put into moulds to
form blocks or rammed into simple
moveable shuttering on either side of a
timber frame wall, 30-60 cm thick. The
mixture must not be rammed hard. The
middle is pushed down with the foot,
while the edges are given a stronger
pressure: they can be beaten down with
a piece of wood. The more compressed
the mixture is, the stronger the wall, but
with a corresponding reduction in ther-
mal insulation.
The different layers need to overlap
each other when rammed within the
shuttering. The holes left after removing
the shuttering are filled with clay. Before
ramming, the timber framework - the
structural part of the wall - is covered
with clay as a sort of impregnation. The
drying time during the summer is
between six and eight weeks, depending
on the weather.
The fibres used to fill the joints
between windows, doors and the tim-
ber framework must have a strong
resistance to rot. The most suitable
fibres are flax and hemp.
Straw bales
It is also possible to use bales of straw
stacked on top of each other as ther-
mal insulation. The size of a bale of
straw is usually 35
Figure 14.16: Wall construction in 'Leichtlehm'.
60 cm, and it weighs about 20 kg, but both the dimen-
sions and the weight vary somewhat, depending upon the baling equipment and
the pressure used to put it together. Hard-pressed bales can even have a struc-
tural capacity. Building with straw bales was very popular in the USA until after
the Second World War. They were used for everything from schools to aircraft
hangars. The structure is usually placed on a damp-proof course on the founda-
tion. The bales of straw must be properly compressed and dry (10-16 per cent)
with no sign of mould or rot. They are stacked up on each other and coursed like
normal brickwork. Between the courses, 70 cm-long stakes are pushed into hold
them together. Extra reinforcement is used at the corners, against the openings,
etc. After two to four weeks the walls are clad with chicken wire and rendered
35
