Civil Engineering Reference
In-Depth Information
products should be avoided. Pure products can be either burned for energy
recycling or composted when they have served their time in the building.
Ordinary disposal can lead to increased nutrients in waste water which seeps
into the surroundings. Certain jute products used for sealing joints are
impregnated before transport.
Grass plants
Many different types of grass can be used as an insulation material in the form
of loose fill, bales, matting or boards: e.g. wheat, rye, barley, oats, hemp, maize,
reed and flax. Further south in Europe, straw is a more common roof covering.
A straw roof has good thermal insulation and moisture-regulating qualities.
Straw roofs are discussed in the following chapter, p. 356.
Loose fill
This is pressed into the structure with lime added to repel vermin. Flax and
hemp have a very high resistance to rot. Straw from corn rye is the most resistant
to moisture. However, the durability of corn-based materials as insulation is rel-
atively limited. Straw stabilized with clay is a better material. It prevents settling,
increases alkalinity and improves resistance to rot.
'Leichtlehm'
During the 1920s in Germany a building technique called 'Leichtlehm' was developed.
Leichtlehm is not structural and needs a separate structural system. A mix of straw and
clay is rammed directly into the wall or produced as blocks, which can later be built up with
a clay mortar. Straw mixed with clay needs a good protective surface treatment, and is
given an extra skin for protection on very exposed sites.
Leichtlehm is produced as follows:
1. All clays can be used. The clay is dried and crushed and poured into a large tub
(often a bath tub!) of about 200-300 litres, ten times as much water is added and mixed
well in. A motorized mixer can be used or the work can be done by hand. About 2 per cent
soda waterglass is added to reduce the surface tension, so that the water can more eas-
ily penetrate the clay particles. This reduces the amount of water required and makes the
drying time shorter.
The clay should lie in the water for two hours. If using wet clay, it should be laid in water
so that it is just covered and left for 24 hours.
2. The mixture is tested: 1 dl of the mixed clay gruel is poured evenly onto a piece of
glass. The diameter is measured. If it is much less than 15 cm, it needs more water. If it
is much more, than it needs more clay.
3. The clay gruel is poured onto the straw until it is totally drenched. Any type of
straw can be used, but rye is best. The stalks are stiffer and thicker than most oth-
ers, so the greatest amount of air is retained in the walls and therefore the best insu-
lation.
