Civil Engineering Reference
In-Depth Information
Scandinavia to boil the timber planks first. This is a very effective way of wash-
ing out the content of the cells.
Burning the outer wood
A traditional way of increasing the durability of wooden piles was to burn the
part that was going to be placed underground. The carbon coating formed lacks
nutrients and is almost impenetrable to insects and fungus. The burning also
enriches the resin and tars in the outermost part of the pile. The greatest impact
occurs on pine, which is rich in resin. Burning spruce and deciduous trees is not
so effective. During burning the timber can easily split, and it is easy for fungus
to creep in through the splits, so burning must be carefully controlled, preferably
by using a blow lamp. The depth of the burning should be 1-3 mm, after which
the surface is brushed with a bronze brush. This process takes a long time.
Julius Caesar described the technique in
De Bello Gallico
in connection with set-
ting up fortification in the Roman Empire. The method has also been used for
centuries by Portuguese and British timber warships, as it not only increased
resistance to rot but also made the surface waterproof.
Oxidizing and exposure to the sun
As late as the nineteenth century it was unusual to treat external walls at all.
Timber developed a silver-grey colour based on an oxidation process caused by
ultraviolet radiation from the sun. Any material applied to a wall will reduce or
block this effect. The oxidation penetrates a few millimetres into the timber mak-
ing an effective, protective layer, but, particularly in damp climates, fungus may
develop. If fungus is discovered, the wall must be washed with liquid green soap
or cleaned by spraying steam.
Untreated surfaces are also exposed to splitting through drying out too quick-
ly. Rubbing in elasticizing agents, preferably linseed oil mixed with a little lime,
increases resistance to fungus. The same technique, using olive oil, was applied
around the Mediterranean for more than 2000 years.
On older log houses the sunny side of untreated walls often becomes a sun-
brown colour. The warmth from the sun draws resins to the surface, which also
forms a protective layer.
Non-poisonous surface coats
The application of a non-poisonous layer on the surface is mainly to protect the
timber from mechanical wear and tear and direct solar radiation. Exposure to
