Wood drying or wood seasoning refers to the process of drying timber, either naturally or using machines, to reduce its moisture content before it can be used.
All of the major wood seasoning methods can be broadly categorised into two: air drying and kiln drying.
The first method, i.e. air drying is a traditional and less expensive technique, which involves leaving wood out in the open to allow air to flow through it freely and reduce its moisture content.
The second technique, i.e. kiln drying, involves the use of artificial means to dry wood using a machine or chamber called a kiln.
Why Wood Needs to Be Dried Before Use:
There are many reasons why wood should be dried before use.
Freshly cut wood has a high amount of moisture. If used before drying, it will eventually dry over time and lose moisture, which will cause the wood to shrink unequally, leading to warping, cracking, twisting, or other damage. Wet wood is also not dimensionally stable.
The higher the moisture content of the wood, the less strong and durable it will be. Drying makes the wood stronger and less prone to insect attacks and other damages due to environmental elements, ensuring a long life and improved performance. Wood with high moisture content is also more prone to attack by fungi and insects.
Moreover, dried wood is easier to work with than wet wood, which can be difficult to cut and join. It is also easier to paint and stain dried wood over wet wood. The drying process also helps reduce the wood weight, which is crucial for construction applications.
Top 10 Wood Drying Methods
There are various methods used for drying the wood, each of which has its own pros and cons. Here are the top 10 wood drying methods:
1. Air Drying
Air drying is the traditional and one of the oldest methods for drying wood. It is a slow process, but it is also the most environmentally friendly and least expensive.
The process involves stacking wood boards on a high platform in a manner such that boards are separated by wood pieces called stickers to allow maximum exposure to the air. The ideal place for air drying should be clean, dry, and shady. The success of the process completely depends on environmental conditions, including the flow of air, humidity and temperature. Wood boards need to be arranged such that a high and continuous flow of air throughout the setup can be ensured.
This is a less controlled method of wood drying. However, it is possible to somewhat control the rate of moisture loss by covering the boards with a water-resistant material, such as mineral oil.
2. Kiln Drying
Kiln drying is a faster & more efficient method of drying wood. It involves the use of heat and airflow to remove moisture from the wood. Kiln drying can produce more even and defined results than air drying, but it can also be more expensive.
Kiln drying is a more controlled method because it allows you to better control the final results by adjusting the various factors when drying wood in a kiln. The process of wood kiln drying involves the following steps:
- Preparation: This involves cutting the wood into the right sizes and stacking the boards using spacers to ensure the free flow of air.
- Kiln loading: The wood setup is shifted into the kiln in a specific arrangement. Avoid overcrowding.
- Adjusting controls: The environment inside the kiln is adjusted using controls for temperature, airflow (speed), and humidity.
- Drying scheduling: Setting up a drying schedule based on species, thickness, and the target moisture content (MC).
- Drying process: First, high temperatures and low humidity are applied to remove most of the water quickly. Then, the wood is processed under reduced temperature and humidity to prevent stress and improve stability.
- Moisture tracking: Moisture metres are used to track MC levels in real-time during the drying process to check the progress and achieve the desired results.
- Quality control & storage: The dried wood is checked for quality in terms of moisture content, stability, etc. and stored in a controlled environment to prevent it from regaining moisture.
3. Solar Kiln Drying
Solar kiln drying is a hybrid method that combines the benefits of air drying and kiln drying. It uses the sun’s heat to dry the wood in a kiln-like chamber, and it can be used in a variety of climates.
One side-effect of kiln-drying is that it is not eco-friendly because of the extensive consumption of energy. The use of solar as an alternative energy source in the kiln drying process helps achieve the desired moisture control without impacting the environment.
The process of solar kiln drying is almost the same as traditional kiln wood drying. However, the kiln used in the process is a little different, as this one has transparent walls to trap solar radiation and convert them into energy to heat up the air inside the kiln.
The dehumidification drying method uses a machine to remove moisture from the air inside a drying chamber. This method is effective in high-humidity environments.
Dehumidifiers are used in a sealed drying chamber to remove moisture from the air and reduce humidity in the chamber. The humidified air is circulated within the chamber and distributed evenly around the wood to make it dry.
This is a rather slower wood seasoning process but it preserves the quality of the wood and reduces the risk of damage due to rapid drying.
5. Vacuum Kiln Drying
This method of timber drying involves the use of a vacuum to lower the boiling point of water in the wood. This method can reduce drying time compared to traditional kiln drying.
This technique of drying wood involves placing the wood in a vacuum-sealed container where the air pressure is removed to speed up the drying process. The boiling point of water falls as the pressure inside the chamber decreases, enabling moisture to be removed from the wood at lower temperatures and faster than regular kiln drying. This method also ensures overall better wood quality and prevents damages like cracking and warping during the drying process.
6. Radio Frequency Drying
Radio frequency wood drying technique uses high-frequency electromagnetic waves to heat the wood, causing moisture to evaporate rapidly. Radio frequency drying can reduce drying time significantly and increase efficiency.
High-frequency electromagnetic waves are applied to the wood, causing the water molecules within the wood to vibrate and heat rapidly (just like in a microwave oven). A special chamber with an RF generator is used, where the wood is placed between electrodes to make the moisture inside it heat up and evaporate.
7. Freeze drying
This method involves freezing the wood and then removing the (frozen) moisture from the wood through sublimation. This method is only used for specialty applications and certain types of wood.
The wood is placed in a freezing chamber and the temperature is dropped, causing the moisture inside the wood to freeze. Sublimation is used to cause the ice to evaporate without melting first.
8. Steam Drying
Timber steam drying applies steam to the wood, increasing its temperature and facilitating moisture removal. This method is usually combined with kiln drying to achieve faster results.
A special chamber or kiln is used where the flow of steam and temperature are controlled to achieve the desired outcome.
9. Chemical Drying
The process uses chemicals to ease the seasoning process. This wood drying method is typically used for specific wood products or in specialised industrial settings.
The process is generally used along with another drying process, usually to speed up drying. It involves applying certain chemicals such as drying agents to remove moisture faster.
10. Hybrid Drying
Hybrid drying can be used to combine the benefits of multiple drying methods. For example, a combination of air drying and kiln drying can provide more efficient and controlled results.
In the hybrid wood drying process, the wood is usually first dried using traditional kiln drying. Then, it is subjected to a secondary drying method such as solar drying or vacuum drying for faster and better results.
In summary, wood seasoning before use is necessary to ensure stability, resilience, durability, workability, resistance to decay and insects, bonding of finishes, weight reduction of wood, and overall quality. Proper drying processes can help optimise or improve the wood’s properties, making it a reliable and valuable material for various applications.
Of all the wood drying methods we have discussed above, kiln drying is the most suitable in terms of efficiency and overall wood quality. However, if you’re looking for a less expensive or more eco-friendly process, go for air drying.
All our wood at White Knight Consulting Ltd. is kiln-dried to ensure the highest quality in terms of wood strength, stability, and durability. We also sometimes use a mix of air-drying and kiln-drying to further improve our results. If you want to know more about our wood drying techniques or are looking to purchase high-quality dried timber at the right price, contact us today.