Civil Engineering Reference
In-Depth Information
drying time should be as short as possible. If the temperatures get too high, how-
ever, splitting or cracking can occur, which can also increase the intake of mois-
ture.
Methods of impregnation
There are many methods of treating timber in order to increase its resistance to
decay:
• Self-impregnation of logs
• Cleaning out the contents of the cells
• Burning the outside layer
• Oxidation
• Application of non-poisonous protection to the surface
• Application of pH-regulating substance on the surface or through impregnation
• Application of poisonous protective layer on the surface or through impreg-
nation.
The last method is a strategy with 'active' impregnating substances; the other
methods can be characterized as 'passive'.
Self-impregnation of logs
The most common method is to chop the top of a pine tree and remove a few
stripes of bark from the bottom to the top. Three or four of the highest branches
are left to 'lift' the resin. After a few years the whole trunk is filled. This dramat-
ically increases its resistance to rot. Houses built of these logs will probably last
for hundreds of years without any further treatment. A double guarantee is
achieved if this is complemented with a cleaning out of the cells and burning the
outer layer.
Cleaning out the contents of the cells
Certain insects, mould and fungus live on the nutritious contents of cells, while
other fungi live on the cell walls. Cleaning out the cells' contents can at least
solve part, if not all of this problem. The method was conceived after the discov-
ery that logs stored under water lasted longer than those stored in air. It must be
assumed that the absorption of salt from sea water also has a positive antiseptic
effect. Where timber boarding is laid on a roof, it has been common practice in
