Civil Engineering Reference
In-Depth Information
than 84 per cent of it. The relative humidity
of air changes with temperature: air holds
more vapour if it is warmer. See Appendix
1 for more information on moisture content
and relative humidity.
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The type of straw is immaterial as long as
the above guidelines are followed. It can
be wheat, barley, rye, oats, etc. Straws
should be long, 150mm (6”) minimum,
preferably 300-450mm (12-18”). Rye would
be a good choice as it contains a natural
fungicide so is very resistant to rot, but
it's almost impossible to get it in the right
size of bales. Winter wheat would be the
second choice as it is more durable, having
had to survive harsher weather conditions.
Bale standard
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Bales should be as dense and compact
as possible. The baling machine should
be set to maximum compression; in
general this means bales contain about
one third more straw than usual. Weight
should be between 16kg and 25kg.
Do not confuse straw with hay or grasses.
Straw is the baled-up dead plant stems of
a grain crop. It has had virtually all its seed
heads removed, and contains no leaves or
flowers. It is a fairly inert material, with a
similar chemical make-up to wood. It does
not decompose easily, usually requiring
the addition of nitrates to do so. Hay, on
the other hand, is grass baled up green,
with lots of feedstuff (leaves, flowers, etc.)
deliberately left in there because it is fed to
animals. It readily decomposes, unlike the
dead plant stalks of straw.
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Bales should be more than twice as long
as they are wide and are usually meas-
ured in imperial units rather than metric:
about 41” (1.05m) long on average is
good. Most baling machines produce
two-string bales that are 18” (450mm)
wide x 14” (355mm) high and are of
variable lengths from 36” to 45” (900-
1125mm), although a few machines are
20” (500mm) wide and 15” (390mm) high.
Mini Heston bales of 7'10” x 3'10” x 2'3”
(2.4m x 1.2m x 0.7m) or Quad bales of 7'
10” x 2'7” x 2'7” (2.4m x 0.8m x 0.8m)
can also be used, and are especially
good for building extremely large spaces
such as warehouses.
The age of the straw does not matter as
long as the above conditions are fulfilled,
and it has been stored correctly. All the
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Strings must be very tight, so that it is
difficult to get your fingers underneath.
They should be about 100mm (4”) in
from the edges of the bale and not
sliding off the corners. String should
be sisal or hemp baling twine for a low
environmental impact, or polypropylene,
but not wire, as metal is best avoided
within a straw wall.
