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Wood Preservation

When the untreated wood is exposed to outdoor and different climatic conditions, it decays and degrades. Therefore, to protect the wood from decay, degradation and also from the harmful attack of termites, a great number of chemical preservatives and processes (largely known as timber treatment, pressure treatment of lumber treatment) are used. The aforementioned protective sheath over the wood increases the life of wood as well as timber structures.
Some efficacious techniques and preservatives that proved beneficial on the wood are listed below:
Kiln Drying
Heat Treatment
Chemical Treatment
Thermal Treatment
Vac-Vac Treatment

1. Kiln Drying

An extremely satisfying process that takes a foot further to preserve and ensure supreme quality of wood materials. Kiln Drying functions by reducing the liquid content of a timber, thus increasing the durability of finely designed lumber products. The drying of wood features in assuring the gross dimensional changes through shrinkage. The wood is parched to a certain level of equilibrium moisture, that is to be attained by wood. Though, the alteration in dimensional will be kept minimum

In this technique of wood preserving, it is impossible to eliminate the dimensional change entirely. But the size can be determined by the chemical modification. Increasing worth of sawn timber products, drying timber is an essential method that works effectively from the primary wood processing industries. If carried smoothly after the felling of tress, drying fundamentally preserves decay, stains, fungus and also harmful termite attack. Timber having 20% below moisture content cannot feed bacterias and organisms which can decay to the wood.

Some other major advantages of Kiln Drying includes the following:
The transportation cost of dried timber is comparatively less because it is easy to handle and lighter in weight.
In comparison to green timber, dried timber is relatively stronger.
For impregnation, timbers should be properly dried for accomplishment of proper penetration , that too in the case of preservatives that are contains oil.
For efficient working and befitting reactions to occur in the domain of chemical modification of wood and similar products, the material should be properly dried following a certain amount of moisture content.
Comparative to green timber, paints and finishes lasts longer on dried wood.
Various properties like that of thermal and electrical insulation, are enhanced by drying.

2. Heat Treatment

Heating timber stands out as a valuable method, without harming or creating a negative impact on the environment. Warming a wood to a certain temperature can decrease the amount of attack by termites. This method is widely preferred rather than chemical preservatives.
Similar to this heat treatment are European heat treatment methods, i.e., Retiwood (developed in France), Thermowood (developed in Finland by VTT), Platwood (developed in Netherlands). With the existence of different kinds of timber, these are treated in the presence in the heat or pressure along with nitrogen or water vapour, to monitor the drying process in a duration of 24 to 48 hours at 180 to 230 degrees of temperature, which may vary according to the type wood. The wood  after being heated appears darker in color and faces various changes in mechanical properties. To avoid splitting,  the treated wood needs drilling for nailing. The treated timber finds application in flooring, furniture, siding and windows.
The reason behind treating wood by heating is that it increases the durability of wood along with dimensional stability and hardness. Though, this type of method gives lesser positive outcome when compared with other wood preserving methods, especially when looked upon mechanical properties.

3. Chemical Treatment/Pressure Treated:

Maintaining a timber is very important, so that it can last for decades. So, chemical treatment, also known as pressure treated method is fundamentally formulated to increase the service life of timber. Chromated copper arsenate (CCA) is the most essential chemical whose effective presence preserves lumber products. This type of chemical treatment infuses the wood cells, thus making them highly resistant to the termites attack, degradation, weather and even fire.
Chemical treatment is a costly method but significantly increases the service life. But this method is cost-effective when used in environment with known biological hazards, thus reducing the maintenance cost. This method doesn't prevent biological degradation but inhibits the degradation when wood is utilized is normal environment.
Preservative method provides safety to timber as well its products, protecting them from various harmful attacks and wood destroying organisms like fungi and insects. Being an effective method, it initiates the entrance of chemicals that prevents fire.
Chemicals used in this process protects sapwood rather than heartwood. Heartwood is impossible to treat because of the presence of resins in heartwood cells and other extracts that restrict the consumption of preservative solutions like that of chemical. This preservative method is helpful in treating sapwood whose plantation includes radiata, hoop pine and slash.

4. Thermal Treatment:

Treating wood thermally is an effective method that significantly improves the condition of wood by using a steam environment at atmospheric pressure which is free from chemical additives. Expanding the usage and areas of application, this method alters molecule in wood composition, thus increasing dimensional stability and protection against decay and shrink.  
Woods treated from this method finds application in both interior as well as exterior objects like furniture, house siding, musical instruments, decks, flooring, windows, door, fences as well as highway barriers. Apart from this, thermo treated wood is ideal for making boardwalks, trim of yacht, swimming pool area, landscape design, bath tub, wash-bowls etc.

5. Vac- Vac Treatment:

Vac- Vac is a simple process of applying organic preservatives on wood. The name of this treatment is derived from the essential mechanical process involved in this process. This method works after sealing  the wood in a chamber, in which a vacuum is pulled to remove the excess air from the wood. Thus adding organic preservatives into the chamber which will later penetrate wood. After the addition of preservatives through a vacuum, the second vacuum is forced inside to take out excess preservative.
This type of method is finds application in those areas which are subject to moisture.

Note- When the wood is treated under pressure it does dry immediately, but is supplied in the same condition. And during the treatment, the compounds will only penetrate the sapwood, that is the outer most part and not inner part that is heartwood.

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