How is Wood CuredPosted by monsterguide
How is Wood Cured
What is Curing?
Wood is ubiquitous and has several applications. Every house uses timber during some part of the construction or for interior decoration. Using good wood for these applications will see that they last long. If the wood is not good, it will decay naturally.
Curing is removal of sufficient moisture from wood so that it can be worked with equipment to make furniture or for any application thereof.
Badly cured wood develops cracks and is rated as bad wood. Under normal curing/drying conditions, time taken for the wood to cure also determines whether it is appropriately cured or not. It usually takes a year or year and half for complete curing, which means to bring the moisture content of wood between 8-12%.
Usually the wood that is intended to be used for furniture is first milled and there it is made into boards/planks or smaller sized logs. It is then subjected to curing because when the wood is directly cured it usually results in cracks and splits, becoming unfit for use. To cure wood, it has to be dried slowly. Fast drying results in the formation of splits.
The following are some of the different curing methods that are followed:
- Air Drying
- Kiln drying
- Air Drying Followed by Kiln Drying
Subjecting wood to natural air is called air drying. Here, there is virtually no control over natural factors such as temperature, relative humidity or speed of the air passing through the wood. Therefore, the speed of drying depends on all these factors.
Air drying is a possibility in dry tropical countries, but in tropical rainy conditions air drying will be very slow due to high relative humidity. For a moisture content of 20 to 25% of the wood the time taken varies from 2-3 months to about 1-2 years. It also depends upon the tree species and the girth and length of the log.
The lowest moisture content that can be obtained with air drying is about 16-17% and the wood cannot be dried below its equilibrium moisture content, which varies according to the atmospheric conditions. Therefore air drying cannot suffice curing of wood intended for furniture manufacture.
A modern conventional kiln can be used for drying timber, with provision for temperature control. Furthermore, kilns allow constant and adequate flow of air over the surfaces of the logs. Huge fans control the rate of the airflow as well as its direction. The temperature and relative humidity of the air can also be adjusted depending on the wood species and quantity of wood being dried. Therefore in a kiln it is possible to cure wood at a fast pace. The temperature can be increased to the extent that the species can tolerate without showing adverse effects.
Additionally, kiln drying can help achieve timber moisture contents suitable for specific applications. In the same kiln, different wood species can be cured to varying moisture contents, as the parameters of curing are controllable.
There is only one minus point with kiln drying in that the cost escalates. Sometimes, the cost of wood can rise because of high investment on equipment, fuel, electricity and manual employment.
Air Drying Followed by Kiln Drying
To reduce the costs involved, there is another method of curing wherein air drying is followed by kiln drying. A conjunctive use of air drying and kiln drying will reduce cost drastically as well as bring in a desirable quality in the timber that is cured. It is worthwhile to have this approach. The amount of kiln drying in this approach depends on the external vagaries as well the extent of moisture to be removed from a particular species.
There are occasions where UV radiation curing is also done; however, the cost factor is high with this method.
Whatever method is adopted, wood has to be appropriately cured and brought to the desired moisture content level. Only then does it become workable and long lasting.