222
IHSE E 2 (
Boric acid 1 part
Zinc chloride 3 parts
Sodium dichromate 4 parts
Water 100 parts 2 ,2 2@sX2RHIA
e!! is done either by spraying, dipping or by brushing the preservative for a
short period on thoroughly debarked timber. For the oil type preservatives, the moisture
content in timber should not be more than 14 per cent. With water soluble preservatives, a
moisture content of 20 to 30 per cent is permissible. At least two coats should be applied. The
second and subsequent coats should not be applied until the first one has dried or soaked into
the wood. Where possible, the treatment is done hot. Surface treatment is used mostly for
treating timber at site and for retreatment of cut surfaces.
consists in submerging debarked timber in the preservative solution for a
sufficiently long period until the required absorption of the preservative is obtained. For dry
vineers 15–30 minutes of soaking are enough.
r g ensures sterilisation against fungi and insects. The timber is submerged
in the preservative solution. Which is then heated to about 90° to 95°C and maintained at this
temperature for a suitable period depending on the charge. It is then allowed to cool until the
required absorption is obtained. During the heating period, the air in the timber expands and
is partially expelled. While cooling, the residual air in the timber contracts and creates a partial
vacuum which causes the preservative to be sucked into the timber. Generally two baths are
used, the first containing water where the hot treatment is given and the second the cold bath
containing the preservatives into which the timber is transferred immediately after heating.
This overcomes the danger of precipitation of chemicals at high temperatures. This arrangement
also helps to make the process continuous in case the quantity of timber is large.
f X Sapwood of almost all green timbers with the bark on and of bamboos in
green condition, soon after felling, can be treated using any of the inorganic water soluble
preservatives by this process. The log of wood attached to the hose pipe and connected to the
reservoir containing preservative at an air pressure of 0.1–0.2 N/mm^2 on its surface is shown
in Fig. 4.6. Due to hydrostatic pressure, the preservative displaces the sap in the wood. The
treatment is stopped when the concentration of preservative at the lower end of the log is the
same as that in the reservoir.
p
2R
T f/
2