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LOGGING
About
Logging
Logging is the process of harvesting trees, sawing them into appropriate
lengths (bucking) and transporting them (skidding) to a sawmill. The
different phases of this process vary with local conditions and technology.
In colder regions, trees are felled by axe in winter and transported by a
sledge drawn by oxen, mules, or horses to a frozen river. After the spring
thaw, the logs are floated down the river to the sawmills.
In the 19th century logging was a hand process. But today, in some parts of
the world it has been mechanized, trees are felled by crosscut saw or
power-driven chain saw. Even trees of relatively young plantations are
felled by a machine that cuts the entire tree in one bite. Trees are then
cut into standard lengths and skidded to the mill by truck or tractor or
conveyed to a central point by cable, either high above the ground
(high-lead and overhead skidding) or along the ground (ground line
skidding). Helicopters and balloons are also used to transport logs.
Local conditions may dictate uncommon logging methods. In India, teakwood
trees are felled by girdling (making a circular cut around the tree through
the outer bark and cortex to interrupt the circulation of water and
nutrients) and harvested several years later. Then, as is also common in
Nigeria, they may be floated down the river by raft. In several Asian
countries, timber is transported by elephants.
Types of
Logs
Laminated Logs
- formed by gluing wooden boards together
& shaping them up into log forms by machines. These logs have a moisture
content of less than 18%; therefore, they can be coated immediately with a
Sikkens system.
Kiln or Air Dried Logs
- are dried by air exposure or in kilns. Generally, their moisture content
is below 18%; however after construction, some logs may have moisture
content higher than 18%. Therefore, it is recommended to allow a six months
drying period before applying Sikkens system. If the moisture content of the
log is unknown, follow the application procedure for green logs.
Green, Wolmanized Timber and Pressure Treated Logs
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these have a moisture content of 18% or higher. Therefore, they should not
be coated with a solvent borne, film-building coating until the moisture
content has been reduced to 18%, or less. Wolmanized timber or pressure
treated logs have all been treated with various chemicals and forced into
the wood under pressure thereby protecting the wood from fungus and from
rotting. The moisture content of these logs is normally above 18%,
therefore, a minimum drying period of 6 months must be observed before
coating them.
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