Most woodworking projects require wood that has been adequately dried. If you want to know more about wood drying methods or the difference between air-dried and kiln-dried wood, you’re at the right place.
Freshly cut trees or green wood usually have a very high moisture content, around 30%-45% and are not appropriate for general woodworking projects. This is why wood needs to be dried to reduce its moisture content to the 6%-10% range before it can be used commercially.
When buying wood, you must always factor in the method of wood drying. In terms of quality, kiln-dried wood is considered superior to air-dried wood, but it can also be more expensive.
Why Does Wood Have to Be Dried Before Use?
If you’re wondering why wood needs to be dried first, here’s your answer.
Wood is a porous material, i.e. it absorbs and releases moisture depending on its environment. Basically, it will try to maintain its own moisture level with that of its environment. In doing so, it will either release or absorb moisture, which will cause it to shrink or expand, respectively.
Suppose that you’re using wood in dry conditions or outdoors where the moisture level of the environment is relatively lower. To adjust to its environment, the timber might release some of its moisture and start shrinking.
If your wood has a high moisture content, it might release a lot of moisture and shrink considerably to even change its shape or appearance, which might also impact the quality of your project.
Drying wood before use will ensure that the moisture content (MC) of the wood is just enough to not cause it to shrink or expand a lot by releasing or absorbing moisture.
What Is the Ideal Moisture Content of Wood?
The ideal MC will depend on a number of things, including the type of wood and the environment where it’s going to be placed. For different projects, the recommended wood moisture levels are as follows:
- Indoor projects – 6% and 8%
- Hardwood flooring – 6% to 9%
- Outdoor projects – 9% to 14%
- Firewood – less than 20%
How to Dry Wood?
There are many ways to dry wood to reduce its moisture content, but the most common wood drying methods used commercially are air drying and kiln drying. We’ll explain these methods below as well as discuss the various differences between them.
Air Dried vs Kiln Dried Lumber
|Method of Drying
|Naturally dried in open air
|Artificially dried in a controlled kiln
|Higher moisture content (10-20%)
|Lower moisture content (6-8%)
|Longer drying time (several months to years)
|Shorter drying time (few weeks to few months)
|Less stable, more prone to shrinkage
|More stable, reduced risk of warping and twisting
|Lower cost due to less energy consumption
|Higher cost due to energy-intensive process
|Retains more of the wood’s natural color
|May exhibit slight color change due to drying
|Outdoor projects, rustic furniture
|Indoor projects, fine woodworking, cabinetry
Air drying refers to the process where the wood is dried by leaving it in the open air. It is a natural wood-drying process and doesn’t involve the use of any machine. The wood is left out in the open. Air-drying is a very slow process as it can take anywhere from 8 to 15 months or even more time for the wood to completely dry.
Kiln Drying refers to the wood drying method where a special chamber called a kiln is used to dry wood under specific temperature conditions and using high pressure. Kiln drying is a more efficient and a lot faster method of wood drying.
Air drying involves cutting wood logs down into flat boards or panels, which are then stacked in a specific manner and put in an open place such that the lumber is properly exposed to natural air circulation. The process is continued for many months until the desired MC level is achieved.
In the kiln-drying process, wood panels are placed in a large over-like chamber (kiln), where a controlled environment is maintained through careful regulating of temperature, humidity, and airflow to achieve quick & efficient drying of wood. The regulated flow of air causes the heat to evenly distribute within the chamber and force out moisture particles from inside the wood.
The kiln drying process is performed in a more controlled environment, as you have better control over the drying conditions and can adjust them based on your desired moisture content. Air drying is less controlled and very unpredictable.
Quality of Wood
Kiln-dried wood is almost always better than air-dried wood in terms of quality.
For one, the kiln drying process doesn’t just extract excess moisture from the wood but also kills a range of wood pests, insects and bacteria to make wood safer to use. Moreover, this wood will be protected from further wood infestations for a long time. Air-dried wood can be prone to natural defects such as cracking, warping, and insect infestation.
The kiln-dried wood is better also because it has a more adequate and measured moisture content, which has been achieved through a calculated process, unlike air drying where achieving a specific MC rating is nearly impossible.
Kiln-dried wood is also resistant to shrinking or warping, as it has already reached its ideal moisture content levels and will not be as affected by changes in its atmosphere, unlike air-dried wood, which can still shrink or expand due to changes in weather.
Kiln-dried wood has lower moisture content than air-dried wood. Air drying is good for projects where wood with 12%-20% moisture content is needed. Kiln-drying method is typically used to achieve the lower moisture content range of 6%-8%.
Due to higher moisture content in air-dried timber, it may be more prone to further changes in shape with changes in the atmosphere.
One downside of kiln-drying in terms of wood quality is that the process might cause the wood to lose colour. Rapid drying can cause internal tensions in wood grains and make the wood absorb moisture quickly unless it’s put in a climate-control environment after kiln-drying.
Air-dried wood might be easier to work with than kiln-dried timber because of the fact that there is no internal tension in the wood grain.
The air-drying process can take several months, sometimes years. The time to dry also depends on the wood species, density, thickness, and atmosphere.
Kiln drying is a fast process and reduces wood drying time considerably. Typically, kiln-dried wood is ready for use within a few days or weeks. The drying time also depends on the wood species, thickness, and the target MC level.
Air-dried wood is not nearly perfect in terms of moisture content, i.e. it may still have a lot of excess moisture and often needs to be kiln-dried before it could be used in a project. This further extends the timeline of the natural wood-drying process.
The only reason why air drying is favoured over kiln drying is the cost.
Air drying, as one can assume, is a very cost-effective method of wood drying. All you have to do is leave your wood out in the open air in a specific arrangement and let nature do its job.
Kiln drying, on the other hand, requires a special setup with high-end machinery and a powerful energy source, which makes it an expensive method of wood drying.
In the long term, however, kiln-drying is said to be more cost-effective than air-drying, especially when applied on a large scale. Kiln-dried wood will last much longer than air-dried wood even without treatment or a lot of maintenance. Air-dried wood, on the other hand, will be of inferior quality and might need to be replaced or maintained very frequently.
Then, there is the cost of time, as you’ll have to wait months for your wood to naturally dry as opposed to kiln drying, which is faster and more efficient.
Air-dried wood is suitable for projects where wood with high moisture content can be used or the moisture content of the wood is not very relevant. Common uses of air-dried timber include basic construction, outdoor furniture, fencing, decking, patio, and other outdoor woodworking projects.
Kiln-dried wood is usually better in quality but also more expensive. It is used in all kinds of applications, particularly interior woodworking and trim, furniture, flooring, cabinetry, doors, windows, etc. This wood is commonly favoured for projects where low moisture content and high stability are required.
To sum up, if you are on a budget and need wood for outdoor projects, air-dried wood can be a good and more affordable choice. Make sure to ask your supplier about the wood drying process that was used on your wood. This will enable you to better handle and maintain the wood you’re using.
Now, you can easily order kiln-dried wood online from the White Knight Consulting Ltd. We have a wide range of wood available in 40+ species of hardwoods and softwoods. We also sell high-quality air-dried wood that has been dried over a period of multiple years to achieve optimum moisture content levels suitable for different projects. Contact us to know more.