Kiln-drying is a common practice in the lumber industry that brings fresh wood to the appropriate moisture content without causing a lot of problems with overly wet wood.
Such problems include warping in dimensional lumber, binding, bulges and small cracks on the surface of the wood flooring, and adhesive failures in treated wood product.
Moisture issues can end up costing you a lot of money. Kiln drying brings the wood into a condition that minimizes the possibility of moisture concerns.
Excess water in wood products negatively affects the state of the finished product and spoils the workpiece. Lumber under the influence of water becomes moldy, a fungus starts in it. The wood structure is porous and absorbs moisture easily.
- 1 So, what is kiln dried wood?
- 2 Air-drying wood
- 3 Kiln drying process
- 4 Types of kilns
- 5 Moisture related problems
- 6 What can be done to prevent this?
- 7 Is kiln dried wood better?
- 8 What is the purpose of kiln dried wood?
- 9 What are the disadvantages of kiln drying?
- 10 Is kiln dried wood real wood?
- 11 Conclusion
So, what is kiln dried wood?
Kiln-dried wood is green wood that has been dried in a conventional kiln (oven). Drying in an oven allows you to control and set the desired indicators of temperature, humidity, and steam. Thus, the wood is brought to the desired moisture level much faster than air-dried lumber. Kiln dried wood will have little to no excess water.
Air-dried wood is the green lumber was simply piled up and left outside to dry naturally. The drying process can take several months or even a year, depending on the wood to be dried. It is important to correctly distribute the wood for even air flow circulation.
It is a natural process that some people would believe is a lot better than kiln drying wood. However, when you leave timber outdoors, you cannot predict all the possible weather fluctuations that it is exposed to.
Kiln drying process
When the trees are felled and brought to the wood production mills, the first step of the kiln drying process is to sort the logs by size and type or by their final purpose. For example, wood for floors is cut into rough layers of the required final dimensions. They need to be adjusted in size before drying begins.
You can air dry the wood or kiln dry it, which disperses the circulating hot air to rid the wood of moisture faster. Each batch for kiln drying should be sorted by size and type, as different types of wood can react to high temperatures in different ways. Skilled workers control temperature according to size and amount of logs.
Then the kiln dried wood is sorted, adjusted to size and sent to manufacturers or directly for sale.
Manufacturers and mill workers invest labor, time, and money in this process to achieve the correct moisture level for the kiln dried wood. But this does not mean that the tree will no longer need to be protected from moisture, even if its kiln dried.
Types of kilns
These ovens can be the fastest to dry and the most energy efficient. Vacuum kilns do not increase the speed, but also improves the quality of the wood.
Low ambient pressure. The temperature of liquid to vapor remains the same.
While conventional drying uses warm, dry flow to remove water from the surface, vacuum kilns can boil water from the inside of the wood. This allows good vacuum kilns to dry very thick wood very quickly. You can dry 12/4 Red Oak fresh from the saw to 7% in 11 days.
Since the kiln dried wood is dried with a steam gradient—steam pressure to ambient pressure—the humidity can be maintained at a very high level. Because of this, a good vacuum kiln can dry fresh 4.5″ thick white oak to 8% in less than a month. Previously, it was considered impossible.
A solar kiln is something in between kiln drying and air drying. These ovens are usually a greenhouse with a high temperature fan or ventilation or condensing system. Solar ovens are slower and changeable due to weather conditions.
Solar ovens are conventional ovens that are typically built by hobbyists to reduce the initial investment cost. Heat is transferred by solar radiation, and internal air circulation is often passive.
A conventional kiln has pipes that radiate heat into its chamber, which is forged from steam or by hot water coils. Then the wood is heated by burning its content of biomass.
Wood is exposed to moisture at all stages of its “existence”. Excessive moisture can lead to rot. Such wood is not ready for use, as its use is very unpredictable. Moisture evaporating from wood can cause it to warp. And too much water will lead to mold and spoilage.
The kiln kills insects and evaporates excess water in the wood. But this does not mean that the timber is now safe from external factors.
What can be done to prevent this?
The amount of moisture must be constantly measured, and the lumber must be held in a controlled environment.
To do this, it is best to purchase a humidity meter that will show you accurate information and prepare you for the consequences.
Is kiln dried wood better?
Wood can be dried to any desired low moisture using conventional and dehumidification kilns or sun drying, but air drying below 18% moisture content is difficult.
The drying time is significantly shorter with conventional kilns drying than with air drying in solar kilns.
This means that when it comes to capital costs, this capital is saved when air drying is used. On the other hand, installation, operation and maintenance of the kilns are expensive.
In addition, air-dried wood takes up a lot of space, which can also cost money.
In air drying, there is little control over the drying conditions, so the drying speed cannot be controlled.
The temperature used in kiln drying will usually kill all fungi and insects in the wood if a maximum dry bulb temperature above 100 F is used for the drying schedule. This is a huge advantage that is not guaranteed with air dried wood.
If not properly air dried (in the sun), the drying speed can be too fast during the dry summer months, causing warping and twisting, and too slow during the cold winter months.
What is the purpose of kiln dried wood?
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.
It is not very popular as building materials, because it is pretty expensive and sometimes completely dry timber is not good for building. Kiln dried wood must be maintained at relative humidity, which is not obligatory with thoroughly finished products.
What are the disadvantages of kiln drying?
The main disadvantages of kiln dried wood can be considered, primarily a high price. Kiln drying wood process requires the work of professionals and the cost of a large amount of resources. All this leads to a high price.
Also, kiln dried wood can sometimes have defects if the drying process is not followed carefully.
Is kiln dried wood real wood?
It is, of course, real wood. The only thing it differs from ordinary wood is the process of drying, which achieves the desired level of humidity and evaporates excess water from the wood structure. Kiln helps to dry the lumber quickly and reach equilibrium moisture content.
With all the variety of drying methods in woodworking industries, natural and convective methods remain the most popular. Such drying allows harvesting lumber in large volumes at a relatively low cost.
Conductive, vacuum, condensation chambers are most rationally used as an auxiliary option when a more delicate drying is required, or it is required to significantly speed up the process without loss of quality.
Kiln drying is a wood drying process that achieves results much faster than air-dried wood.
Wood dries while being put in a special oven with a heat pump system, that is a quick and effective way to prepare green lumber for sale. The whole kiln drying process must be thoroughly watched and controlled by skilled workers, therefore kiln dried lumber is more expensive than other types of timber.
Kiln dried wood is a fast and easy way to get ready-to-be-used material, although it is a little expensive.
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