Everything You Need to Know about Kiln-Dried Wood in a Nutshell
Wood has been the bedrock of the furniture and construction industries for centuries. However, freshly felled wood cannot be used to make furniture or in construction. It needs to be processed to bring out the desired properties such as strength, flexibility, and ability to work with adhesives.
One of the most common wood drying processes is kiln-drying. Kiln-dried lumber is often used to make furniture as it lasts longer and has relatively high strength. The reason it can last longer is that kiln-dried wood has low moisture content.
Let’s take a closer look at what kiln-dried wood is, the drying process works, and its benefits.
A.) What Is Kiln-dried Lumber?
Before we answer this question, let’s first understand what a kiln is. A kiln is a furnace or an oven designed for drying and baking materials like clay and wood. With a kiln, you can control temperature, airflow, and humidity levels, resulting in better quality dried lumber.
The biggest advantage of using a kiln is that it speeds up the process of drying. So, most wood production mills use this oven to bring down the moisture content of the green lumber to the desired level. The purpose of this process is to keep the moisture at a level where it won’t cause further damage. Kiln-drying can help avoid warping and twisting of lumber during furniture making.
B.) Understanding the Kiln-drying Process
Unlike air-drying, kiln-drying takes place in a closed chamber. You can control airflow, temperature, and humidity inside this closed chamber to bring down the moisture level.
1.) Primary Goal of Kiln-drying
The two primary goals of the kiln-drying process involve moving the moisture to the surface of the timber and letting it into the atmosphere. That’s where the trio of controlled airflow, temperature, and humidity comes in.
While the airflow and relative humidity in the kiln helps with the evaporation of the moisture in the timber, increasing temperature speeds up diffusion, which helps to drive moisture to the surface.
2.) Kiln Schedules
If you maintain the given temperature, airflow, and humidity, the kiln-drying process takes longer. However, periodically changing these factors can help you reach the Equilibrium Moisture Content (EMC) quickly and efficiently.
Usually, you need anywhere between five to eight kiln schedules to complete the process. However, you may need more cycles depending on the species, moisture content, and size of the timber.
3.) Kiln Structure
A typical kiln consists of the following:
- Kiln Chamber: Usually, wood mills use bricks and concrete structures. But, aluminum-built kilns are becoming increasingly popular as they are lightweight.
- Heat Supply: The heat can come from various sources such as heating pipes, heat exchangers, or radiators running on fossil fuels, electricity, or renewable energy.
- Humidifiers: Humidifier systems use atomized water sprays or perforated pipes to inject steam into the wood.
- Fans: Fans, when placed on the roof and in the walls, provide air circulation required to release the moisture into the atmosphere.
4.) Types of Kilns
The three most common types of kilns are Conventional, Dehumidification, and Solar. Let’s know more about them.
- Conventional: It comprises steam or hot water coils or a furnace, which acts as the source of heat. The water removed from the wood turns into moisture through evaporation, which is then sucked out by the ventilators or fans. Although this wood drying process offers excellent results, it is highly energy-intensive.
- Dehumidification: This kiln-drying process requires the use of a heat pump system to remove water from the wood. As you can recycle the heat used in this process, it is more economical and efficient.
- Solar: In a solar kiln, you can use a solar collector to provide the required heat. However, getting kiln-dried logs from this process is unpredictable as it depends on the weather. A cloudy sky means bringing the kiln-drying process to a complete halt.
5.) Before Starting the Kiln-Drying Process
Before sending the timber to a kiln, it needs to go through the following:
- Debark and sort felled trees into logs by species, size, or by end-use.
- Cut the logs into timber or lumber as required.
- Sort the timber by species and dimensions to make the wood-drying process faster.
6.) After Finishing the Kiln-drying Process
Before the end-users buy kiln-dried wood, it goes through the following:
- Once the wood reaches the correct moisture level, you need to plane it into final dimensions.
- Sort it depending on the grade and ship it for the desired application.
- Prevent the kiln-dried lumber from absorbing moisture further down the line.
C.) Kiln-Dried versus Air-Dried Lumber
Just like kiln-drying, air-drying is also a well-known wood drying process. In air-drying, you need to stack pieces of lumber with spacers between each. You can put a canopy or timber on the top for protection and let nature take its course.
Both processes come with a few unique benefits and drawbacks of their own.
|Air-Dried Lumber||Kiln-Dried Lumber|
|Air-drying doesn’t kill any insects, eggs, bug larvae, mold, and fungi in the wood, leaving it vulnerable to a potential infestation.||As kiln-drying process uses heat (170F), it kills most of the insects, eggs, bug larvae, mold, and fungi. So, kiln-dried logs and furniture can last relatively longer.|
|Air-dried lumber may require chemical treatments to increase its lifespan.||Kiln-dried lumber doesn’t require any harsh chemical treatments as the heat effectively sanitizes it.|
|During air-drying, resins continue to be liquid and runny.||The heat in the kiln dries off the resins in softwoods.|
|Air-drying is a natural process that can take up to 8 -16 months, depending on the species of wood.||Kiln-drying, on the other hand, usually takes 6 – 8 weeks.|
|This process doesn’t introduce any internal tensions in the wood. So, you can easily work on it using hand tools.||Kiln-drying, however, can cause the wood to shrink. That, in turn, makes the wood fragile, breaking it off when using hand tools.|
|While air-dried wood may absorb moisture, it doesn’t swell because the cells collapse and compress as the timber air dries.||After coming out of a kiln, the dried lumber needs to be kept in a controlled climate. When exposed, it starts absorbing moisture and may start swelling.|
|Air-dried wood is often moister in the middle compared to the edges as the drying process is not uniform.||Kiln-dried wood dries uniformly in a closed chamber.|
D.) Benefits of Kiln-dried Wood
The primary goal of this process is drying wood for furniture. Furniture made from kiln-dried wood comes with the following benefits:
- It is lightweight. So, moving furniture is easy.
- Kiln-drying prevents the wood from warping or developing small cracks over time, resulting in extremely durable furniture.
- Kiln-drying can remove as much as 9/10th of the moisture, making it resistant to fungal decay.
- It also kills insects, larvae, eggs, bugs, and mold, increasing the life of the furniture.
- You can finish kiln-dried wood relatively quickly.
- It minimizes defects in the wood, increasing its workability.
Owing to these qualities, most US-based furniture makers like us use kiln-dried wood for furniture making.
Whether or not you want to buy kiln-dried wood furniture is a matter of personal choice. It does offer a few unique benefits. You can use it for making various items, including furniture, cabinets, and flooring. If you decide to buy kiln-dried wood furniture, hopefully, you can make an informed decision after reading this post. Do let us know if you have any doubts or questions about kiln-dried lumber in the comments section.