Seasoning of Timber: Exploring Natural and Artificial Methods for Wood Seasoning

What Is Seasoning of Timber?

Seasoning of Timber is a hydrothermal treatment of Timber, involving evaporation of moisture content in required proportion.

Timber Seasoning increases the strength of timber, eliminates wood rot, prevents changes in the dimensions and shape of the articles made of timber, and ultimately improves the quality of finishing of timber.

The basic function of seasoning of wood is to reduce the moisture content to a level appropriate for the use of the articles made from it.

Types of Seasoning of Timber

The following are various Methods of Timber Seasoning,

• Natural seasoning
• Artificial seasoning

1. Natural Seasoning of Timber

This natural seasoning of wood may be in the form of,

1. Air seasoning
2. Water seasoning
3. Solar Seasoning

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1. Air Seasoning

Air Seasoning is the oldest, traditional, and simplest method of seasoning timber. In air seasoning, timber is stack in the air and the rest of the work is allowed to carry out by atmospheric heat and the natural air movement.

These components remove the subsequent amount of moisture content from timber. Air Seasoning is based on the principle that the piece of timber is stacked in a way to allow plenty of air to circulate around each piece of timber.

Care should be taken that there is a sufficient amount of gap between each piece so that air can then circulate around and through the stack. Moisture is removed in a slow and steady manner over a period of time called as seasoning of timber.

2. Water Seasoning of Timber

Water Seasoning is the process of placing logs in a river with thicker ends pointing upstream side of the river for seasoning purposes.

Logs are tied in stacks and such stacks are anchored to a standing tree or hard support to ensure it is not carried away by the river.

The sap of timber is washed over a span of 2-4 weeks by the river water. Logs are then taken out for further processing for completing the seasoning of timber. Stacking of the same is done in the next step in a dry place.

This method or type of seasoning takes lesser time as compared to air seasoning. However, a river is required to wash sap of wood logs; hence this method is not suitable everywhere.

3. Solar Seasoning

Solar Seasoning method is a solution provided for the low energy requirement of air drying and the speedy operation of kiln drying.

Solar Seasoning of timber provides a compromise for various drawbacks of other types of seasoning operations.

For example, the energy input is variable in the kilns which often leads to having effective insulation to hold the heat inside at night time.

Also, some kiln seasoning operations developed temperatures of over 40^oC inside even when the external temperature is -20^oC.

Solar Seasoning could be called the slower and gentler form of kiln drying. Various past research has come to the conclusion that using timber solar dryers, significantly reduces drying time and drying defects compared to air dryers.

2. Artificial Seasoning of Timber

The various methods of artificial seasoning are,

1. Boiling
2. Kiln seasoning
3. Chemical seasoning of Timber
4. Electrical seasoning of Timber

1. Boiling

Seasoning of Timber through boiling provides sufficient characteristics properties for the specific functioning of timber.

Timber is immersed in water in this method and then boiled for about 3-4 hours under supervision. Boiling removes the required amount of sap present in the water.

This process could also be carried out by passing the stream over the timber instead of boiling. The boiling process is fast but the energy required for boiling consumes the economy. Hence the process is time-saving but is costly.

2. Kiln Seasoning of Timber

Kiln Drying is one of the common processes among the many commercial processes for the seasoning of timber.

In this process driving out of moisture is accelerated by using external energy which in turn accelerates the seasoning of timber.

Here the timber is stacked in the same as that in air-drying process, which is then placed inside a chamber capable of changing the conditions to provide the best seasoning results. Conditions in the kiln can be changed as per the requirement of seasoning.

Hence cell characteristics are kept different for each species which requires different drying schedules. The time duration of timber in kiln varies from 2 to 7 days as discussed earlier.

Kiln supervising tool is developed to keep a check on kiln conditions and determine kiln-drying schedules for different species of timber.

Reconditioning chamber determines the damage caused to cells of timber near-surface and refills the moisture back into the outer cells, ultimately removing the effect of seasoning collapse.

3. Chemical Seasoning of Timber

The timber used for high-value applications is seasoned through this process of chemical seasoning. This process is suitable for the timber completely free of surface checks, having applications in rifle butts, golf club heads, and carvings.

Chemical Seasoning is also known as a salt seasoning as the timber is dipped in a solution of sodium chloride or sodium nitrate.

Salts such as sodium chloride or sodium nitrate are capable of drawing out the inner moisture of timber.

Uniform seasoning is ensured across the cross-section of timber using this chemical seasoning as a preliminary treatment.

Chemical Seasoning involves hygroscopic chemicals for soaking the moisture content of green timber, in order to slow down the rate at which moisture is lost.

4. Electrical Seasoning of Timber

Electrical seasoning involves the passing of high-frequency alternating current is passed through the timber. Electrical current introduced in the timber is capable of generating heat which in turn starts drying of timber.

Drying of timber through this method is done under the supervision of experts to ensure safety. As the seasoning of timber has proceeded moisture content reduces to a considerable level and resistance to electricity increases.

This resistance offered to the electricity calculated to know the seasoned timber level. Though this method is costly it is adopted by many plywood companies like this method is fast as well as uniform.

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5. Microwave Seasoning

Microwave seasoning of timber is not a frequently used method of removing water content but may function as an alternative tool to air dryers to facilitate and ensure faster and remarkable wood quality drying.

This process of timber seasoning is an established technology in Canada that is also used for drying some commercial sizes of North American softwood timber.

Microwave seasoning of timber involves pulsed microwave energy which is directed into layers of timber to be seasoned in a way such that it will drive the moisture out of the timber at a frequency that will not cause the seasoning to get degraded.

Objectives of Seasoning of Timber

Following are the reasons for which seasoning of timber is done,

• The economical reason for seasoning timber is to reduce shipping charges.
• Seasoning of timber reduces the weight of timber up to a considerable amount, which results in the easy transportation of timber and less fuel consumption of the vehicle.
• After the seasoning of timber, it serves the purpose of increasing the durability, such that the design life of the component increase to a specific duration.
• One of the important reasons for seasoning timber is to have a check on injury caused by the insects and to prevent decay before the timber is placed in service.
• Seasoning prepares the wood for its injection with preservatives and for other industrial purposes.
• For the safety measures, timber should not shrink more than some specified value once placed in service. Seasoning of Timber has the property to reduce the shrinkage of timber.
• Moisture in timber is an absolute requirement for its decay. Timber or wood which can be kept dry by using the principle of seasoning is less likely to undergo decay.

Improved Ability by Seasoning of Timber

Timber seasoning improves following properties of wood,

1. Strength

An increase in strength, especially tensile, compressive, and bending is observed after Seasoning. Stiffness is also affected with seasoning of Timber.

This concludes that construction of buildings taken place under green strength ratings of timber become stronger in service as the timber dries.

2. Hardness

Seasoned Timber becomes much harder than its actual hardness in the wet state.  Although it has disadvantages if you wish to drive nails into seasoned hardwood, however, it is an advantage as flooring and furniture become more resistant to damage from bumping and knocking.

3. Weight

Reducing the water content of timber from its original green value to 10 to 15 percent results in an efficient reduction in weight. It is beneficial for handling and reducing the cost of transportation.

4. Durability                                        

Timber with 24% or more moisture content is more likely susceptible to rotting and staining fungi. This further results in softening of timber and causes unattractive stains.

Hence in order to avoid downgrading of timber appearance, it is seasoned and kept below 24% moisture content in a protected situation to ensure its indefinite life.

5. Painting and Finishing

To obtain satisfactory results Seasoning of Timber is mandatory before painting, varnishing, or polishing. Not following the seasoning protocol might results into results in peeling, cracking, or blistering of the surface coating due to the presence of moisture content on the surface.

6. Gluing

The bonding of adhesives with timber is also dependent on timber quality. Adhesives will make the strongest bonds when the timber has been properly seasoned. Moisture from a separating layer between timber and adhesive hence bonding strength decreases.

7. Resistance to Insect Attack

Insect Attack is more prominent in the case of unseasoned timber. The range of insect species that are liable to attack timber is limited in seasoned timber.

Species of insects are treated by preservation to resist attack. In such cases, partial seasoning may be required to carry such a treatment.

8. Electrical resistance

Electrical resistance in the case of Seasoned Timber is increased by an approximate factor of a million. Green timber with a good amount of moisture content is no doubt a good conductor of electricity, but on the other hand, dry timber is an insulator.

9. Heat content

Some types are timber are used for ignition, those timbers are required to have a good calorific value to burn easily.

Seasoning of Timber provides timber a calorific value of about 16 to 19 MJjk g to ignite wood easily and burn in a better way causing less smoke to have a check on pollution.

Significance of Timber Seasoning

Significance of Seasoned Timber is as discussed below,

1. Timber that is seasoned gains several qualities with the loss of moisture.
2. The strength of Timber tends to increase after seasoning.
3. The tendency of timber to split, shake or warp decreased, hence seasoned timber is much easier to work with.
4. Seasoned Timber is safer when used in machines.
5. Artificial Seasoning of timber will dry up the sap that creates an environment for fungi and parasites their living.
6. Seasoning of Timber reduces the weight of Timber making them significantly lighter for their transportation.
7. It is well-known fact that if timber is kept dry it will be less prone to decay.

Advantages of Natural Seasoning

Advantages of Natural Seasoning is as follows,

• Less investment cost is required.
• It is best suited, to non-uniform and low market demand.
• Natural Seasoning operation does not require skilled labor.

Disadvantages of Natural Seasoning

Natural seasoning has following disadvantages,

• A large piece of land is required for carrying out the seasoning.
• Desired moisture content may not be obtained.
• The process of seasoning is very slow and on average takes 2-4 years as it depends on natural air, we have no control over it.
• Non-uniform seasoning of timber is obtained.
• Attack of fungi and insects cannot be avoided during the process.

Advantages of Artificial Seasoning

Advantages of Artificial Seasoning are as listed below,

• Seasoning of timber is uniform, hence considerable defects such as shrinkage, cracks, and wrapping are minimized.
• Removal of moisture content is fast, hence the process becomes economical.
• Fungi and insects attack is reduced.
• Painting and finishing of timber become effective.

Read More: What Is Wood | 35 Types of Wood | Wood Types | Wood Names

Disadvantages of Artificial Seasoning

Disadvantages of Artificial Seasoning is as given below,

• The cost of processing is high.
• Time to time supervision by skilled personnel is required.
• Uneconomical if the demand for timber in the market is less.

Conclusion

In conclusion, the seasoning of wood is also called as wood seasoning, and it is crucial process which significantly impacts the quality and performance of timber, also through natural or artificial methods, wood seasoning or timber seasoning involves reducing the moisture content for improving its stability, durability and workability.

Natural seasoning of timber allows it to dry slowly over time and it taking into account environmental factors such as circulation of air and protection from direct rain and sunlight, also this method is time-consuming but yields timber with enhanced strength stability.

Artificial seasoning, on other hand, involves controlled conditions like a kiln drying or specialized drying chambers to accelerate the drying process, this method offers faster and more uniform results, reducing the time required for timber to reach the desired moisture content.

Proper seasoning of timber is vital to minimize the risk of warping, decay and cracking, it improves the dimensional stability, strength and resistance to fungal growth, making the timber suitable for various application and including it construction, wood working and furniture making.

By following established guidelines and utilizing appropriate seasoning methods, the performance and quality of timber can be maximized ensuring its long term sustainability and usability.

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