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< prev - next > Manufacturing handicraft process industries Wood and bamboo KnO 100352_Non poisonous timber protection (Printable PDF)
Non-poisonous timber protection
Practical Action
Low toxicity preservatives
Chemical treatment may still be necessary in high-risk situations. If the protective measures
described previously are employed, the preservatives used can be 'natural' or of low toxicity thus
reducing, if not eliminating, health and environmental hazards.
Borax is a fire retardant. It is also effective as an insecticide and a fungicide. Dissolved
in water, it can be applied by brushing. Leaching is reduced by adding a binder such as
a natural resin.
Soda (sodium carbonate) is boiled in water and applied by brushing. Whilst drying,
certain substances in wood which attract harmful organisms are decomposed.
Potash is a traditional preservative for outdoor application, made by boiling wood ash in
water and diluting the solution. It contains the same protective substances such as
potassium carbonate and sodium which are present in the bark of trees.
Linseed oil mixed with turpentine is applied by brushing and provides a tough, water-
repellent surface.
Beeswax is an ancient wood preservative for indoor use. Heated and applied thinly with a
soft cloth it seals cracks and pores. Its resistance to water is low but this can be
improved by adding a natural resin or oil.
A note about paint
The surface of wood can be protected by
water-repellent paints. Paint can only be
applied on fully seasoned timber. If paint
is applied on wood that is not seasoned,
then blistering, flaking, peeling, or mould
growth will result. The complete sealing of
well-seasoned timber can be
advantageous, but requires regular
renewal as damaged portions can be
attacked by insects and moisture. Sharp
edges should be sand-papered to ensure a
uniform application of paint (Figure 7).
Sanded edge
Figure 7: Paint on a timber surface
Disaster mitigation
Most of the chemical preservatives used today contain highly toxic pesticides, which not
only destroy harmful organisms, but also a number of useful ones. Several pesticides are
now known to cause serious health problems amongst larger animals and human beings,
and are suspected of causing cancer and birth defects. However the most serious problem
is their persistence which makes their safe disposal impossible.
As in the case of DDT, which is well documented, the chemical gradually enter the food
chain via the soil, groundwater and water bodies, where they are absorbed by microscopic
organisms and plants. As these are eaten by larger creatures, which serve as food for still
larger animals, the dosage of poison is increased 10 to 100 times at each stage. By this
process of bio-amplification, DDT and several other pesticides are now found in nearly
every living organism.
On account of this, many pesticides have been prohibited in the industrialized countries,
but they are still being produced for and widely used in most developing countries. This
chemical time-bomb is the real disaster that needs to be mitigated. As one important step
is to reduce greatly or, wherever possible, completely stop the used of toxic chemicals for
timber preservation.