Methods of Seasoning

There are two broad approaches to seasoning, viz.,

1. Natural seasoning
2. Artificial seasoning

1. Natural Seasoning

There are two methods of natural seasoning, viz., air seasoning and water seasoning.

(i) Air Seasoning

It is also known as air drying. In this method timbers intended for seasoning are stacked in a dry place under cover about 30 cm above the floor level. Here the longitudinal and cross pieces are arranged one upon the other leaving space for free circulation of air (Fig. 10.9). It is better to provide a foundation to keep the timber clean off the ground. Wood seasoned by such a process can be used for carpentry work after two years.

Figure 10.9 Typical air seasoning of timber

(ii) Water Seasoning

This method of seasoning timber is to completely immerse the logs of wood in water soon after cutting. This is better done in a running stream of water with the longer ends of the logs being kept pointing upstream. By this arrangement the sap, sugar, gum, etc. are leached out of the logs and in turn replaced by water. After adequate soaking the logs are dried in an open place. Although it is a quick process, it reduces the durability of the timber.

2. Artificial Seasoning

Artificial seasoning may be done by kiln seasoning, chemical seasoning and electrical seasoning. By artificial seasoning the moisture content can be brought under control from 4% to 12%. This is a quick process.

(i) Kiln Seasoning

In this system, complete control of temperature and humidity is maintained with proper air circulation and ventilation system. The timber is kept inside an airtight chamber. As a first step fully saturated air at 35–38°C is circulated. Then the humidity is reduced slowly followed by an increase of temperature till the moisture in the timber is reduced to the degree of moisture required. Then the kiln is slowly cooled. This process takes about a fortnight during which the timber is kept on a trolley. The quality of wood obtained by this method is inferior to those seasoned by natural methods.

(ii) Chemical Seasoning

This method of seasoning is also known as salt seasoning. In this method the timber is immersed in salt solution. After a specific period it is taken out and seasoned in the ordinary way. In this method of seasoning the interior surface of the timber dries before the exterior dries out. Here the chances of formation of external cracks are reduced.

(iii) Electrical Seasoning

This method is based on the principle that heat is produced when poor conductors are placed in the field of high frequency. Here, an induction coil producing field of high frequency is set up. The timber is made to pass through the coil. Due to electric induction the moisture is removed instantly and the wood is dried quickly. By this process the moisture gets evaporated uniformly and results in superior quality of timber. Because of high cost this method is not generally recommended.