Civil Engineering Reference
In-Depth Information
of straw and do not treat their crops with
commercial fertilisers or pesticides, which
gives it some advantages over non-organic
straw in that it is longer and will not rot
down quickly. Clay plasterers report that
organic straw has a natural waxy surface
that prevents uptake of water, which is not
what they want for plastering but is what
we'd like for wall building as it is more
durable. Allergy sufferers also find organic
straw easier to live with as it doesn't contain
chemical residues. Sometimes organic straw
can contain a lot of weeds, which makes it
more like hay than straw, so it needs to be
selected carefully. In fact, however, it is
usually quite hard to find organic straw
bales, because it is mostly used by the
farmers who grow it and is not sold on.
not be damp, and must be protected from
damp during the building process. Safe
moisture levels for the prevention of fungal
and bacterial growth are as follows.
Moisture content
Moisture content should not exceed 25 per
cent dry-weight basis
. This means that the
weight of water in the bale should not be
more than 25 per cent of the weight of the
same bale if it was thoroughly dried. Or,
moisture content should not exceed 20 per
cent wet-weight basis
, meaning that the
weight of water in the bale should not be
more than 20 per cent of the weight of the
same bale when wet.
How to choose good
building bales
Relative humidity
Relative humidity should not exceed 84
per cent
.
This means that whatever the
maximum amount of water vapour the air
can hold before that vapour condenses out
as water, the bales must not contain more
Bales should be dry, well compacted with
tight strings, be of a uniform size and
contain virtually no seedheads. They must
A TYPICAL BALE
Width 18” (450mm)
Folded side
Height 14” (355mm)
Wedge or flake
'YXWMHI
Length 36-45” (925-1150mm)
Twine or ties
