In which type of seasoning is timber immersed in a solution of suitable salt, and then taken out and seasoned in an ordinary way?
💧 The Purpose of Timber Seasoning
Freshly cut timber, known as green timber, contains a large amount of moisture or sap. If this timber is used directly, it will shrink, warp, and crack as it dries out over time. Seasoning is the process of drying out timber in a controlled manner to reduce its moisture content to a suitable level (typically 10-20%).
The main goal is to dry the interior of the wood at a similar rate to the exterior to prevent stresses that cause defects like cracking and checking. Different methods are used to achieve this.
📝 Detailed Analysis of the Options
(a) Water seasoning
This method involves submerging the timber in running water. The water leaches out the sap from the wood. It is a slow process and does not involve any salts.
(c) Kiln seasoning
This is a rapid, artificial seasoning method where timber is placed in an airtight chamber (a kiln). To start the process, fully saturated air with a temperature of 35°C to 38°C is introduced. The temperature and humidity inside the kiln are then carefully controlled to dry the wood quickly and uniformly.
(d) Boiling
In this method, timber is immersed in water which is then boiled for about 3-4 hours. This is a quick method to remove sap but it can negatively affect the elasticity and strength of the wood. It is a form of water-based seasoning, not chemical.
(b) Chemical seasoning
This is the correct answer. In chemical seasoning (also known as salt seasoning), the timber is immersed in a solution of a suitable salt, such as urea or sodium chloride. The salt solution is absorbed by the outer layers of the wood. Because of this, the inner surface of the wood dries before the outer surface. This reduces the possibility of external cracks forming and ensures more uniform seasoning.
📊 Comparison of Seasoning Methods
| Method | Process | Key Feature |
|---|---|---|
| Chemical Seasoning | Immersed in salt solution, then air-dried. | Dries from the inside out; reduces cracking. |
| Kiln Seasoning | Dried in a chamber with controlled heat/humidity (starts at 35-38°C). | Fast and controlled, but expensive. |
| Boiling | Immersed in water and boiled for 3-4 hours. | Quick but can reduce strength. |
| Air Seasoning | Stacked in open air under cover. | Natural, cheap, but very slow and requires large space. |
💡 Study Tips
- Chemical = Salt: The key identifier for this method is the use of a "chemical" or "salt" solution. If the question mentions immersing wood in a salt solution, it's chemical seasoning.
- Inside-Out Drying: Remember the unique principle of chemical seasoning: it forces the wood to dry from the inside out, which is the opposite of most other methods. This is its main advantage in preventing surface defects.
- Distinguish from Preservation: Don't confuse chemical seasoning with chemical preservation. Seasoning is for drying the wood, while preservation (e.g., with creosote) is for protecting it from insects and decay.