Reduction of moisture content along with improving some qualities before the use of woods is called seasoning of timber. By seasoning, generally, the moisture is reduced to about 15% where new cut woods bear about 50%.
Reasons for Seasoning
Seasoning of timber is done to fulfill some specific requirement. Followings are the reasons to perform timber seasoning.
- To change and improve the properties of wood.
- To make a correct percentage of shrinking of woods.
- To make a confident use of woods.
- To reduce the adverse behavior of woods.
Methods of Seasoning of Timber
There are mainly two methods of seasoning of timber. These are:
- Natural Seasoning
- Artificial Seasoning
Following tree diagram can be used to illustrate all the methods of timber seasoning.
Detail explanation along with advantages and disadvantages of these methods of seasoning is discussed below.
Seasoning of woods or timbers using natural elements is called natural seasoning. eg. water and air seasoning.
a. Water seasoning
Removal of wood sap immersing logs into water flow is called water seasoning. It is carried out on the banks of the river while thicker ends are kept towards upstream. After that, the logs are allowed to dry. Disadvantage: It is time consuming such as 2 to 4 weeks generally.
b. Air seasoning
Exposing the woods to air for seasoning. At first, a platform is required that is built on the ground at 300mm height above the ground.
Secondly, the arrangement of woods in layers. Air circulation is maintained between logs because it helps to reduce the moisture which is important for seasoning. The environment for this need to maintain some conditions. A clean, shady, dry, cool place is preferred. Sometimes logs are coated by the impermeable substance to reduce extreme moisture. To improve the quality oil coating, thick paint coating is maintained. To prevent fungal infection logs are treated with petrol or gasoline.
- Good quality of seasoned wood.
- A large amount is convenient in this process.
- Well-seasoned timber is formed.
- It’s a slow process.
a. Seasoning by Boiling
Seasoning by boiling wood logs in hot water is called seasoning by boiling. Drying is done after proper boiling. For a large amount of wood, it is done in an enclosed place where hot steam is passed.
- It takes a short amount of time. Generally, 3-4 hours is good enough.
- Develops the strength and elasticity.
- It is serviceable basically for a small quantity of wood, not convenient for a large amount.
- The cost is high.
b. Chemical seasoning
Reduction of moisture using salt solution is called chemical seasoning. After the absorption of water by the solution logs are let to dry.
- It increases the strength of the timber.
- It is less time-consuming.
- Chemical reagents can sometimes reduce strength.
- It can cause a problem in gluing or finishing or corrosion while using.
c. Kiln seasoning
Seasoning of wood by using a large chamber or oven where there is a good process for the circulation of hot air.
- Most effective and economic seasoning.
Kiln seasoning can be done by 2 processes such as:-
- Progressive kiln Seasoning: Wood log is entered through the kiln ant the temperature and humidity differentials are maintained through the length of the kiln to maintain proper drying.
- Compartmental Seasoning: Its maintained by enclosed container or buildings. Advantage: It accelerates the process because external energy is used.
d. Electrical seasoning
Dry wood is non-conductor of electricity while green timber is a conductor, so, can pass alternating current. Thus in this method alternating current is used for drying the cells of wood by creating heat. As electricity is used, it’s called electrical seasoning.
- Using this method quick drying is obtained. a French electrical seasoning method is used to season overnight.
- The equipment required is very costly.
- It is an uneconomic process as a high rate of electricity is consumed.
- During heating the cells of wood or timber they lose their strength and become weak.
Qualities Improved by Seasoning
By seasoning, some common known qualities are improved which are mentioned below:
- Painting and finishing
- Resistance to insect attack
- Electrical resistance
- Heat content
Following precautions must be taken during seasoning of timber.
- During seasoning, the moisture should be removed under an environment maintaining conditions.
- Moisture should be extracted almost at an equal rate from all logs because differentiated dryness causes irregular shape.
- Seasoned timber should be protected from exposure to the rain and excessively high humidity during air seasoning
- During seasoning, a proper gap between logs should be maintained for easy and uniform air or water or hot air passing.