Seasoning of Timber

Grade 8

Seasoning logs

What is seasoning of timber

When a tree is cut down the wood contains a large amount of moisture. It would not be wise to use the wood in this wet state. The moisture must be dried out and the controlled pro cess of doing so is called seasoning.

How does moisture affect timber?

• The water will affect timber in many ways, for example

• Strength properties will be reduce• Fungal attack is over likely• The timber is vulnerable to some species of

wood destroying insects• There excessive weight due to the amount of

water present • The surface finish is unsuitable to receive either

paint or polish• Adhesives will have minimal holding properties

Methods of seasoning

There are two methods of seasoning:• air seasoning, sometimes called natural

seasoning, • kiln seasoning.

Air seasoning• The easiest way, but not the most effective method of seasoning timber, is

to stack it outside. The timber is laid out as seen in the diagram below. It is normally placed in a hut / building, with two sides open to allow air to circulate. The roof and two other sides keep the timber relatively dry. The circulation of the air slowly dries the timer. However, this techniques does not give a precise moisture content. This is because air circulates freely and carries moisture, depending on the weather and the time of year.

The spacing sticks keep the seasoning boards a short distance apart. The air flows between each of the seasoning boards, allowing them to dry slowly. In this way warping is kept to a minimum.

The seasoning time varies depending on the thickness of the wood boards and the time of year. Usually three to four months for 25mm softwoods. The time is doubled, for wood twice as thick. Hardwoods of 25mm thickness require about six months and up to at least a year for 50mm boards.

Air seasoning

Air Seasoning- Advantages

Advantages of Air Seasoning• No expensive equipment needed• Small labour cost once stack is made• Environmental friendly-uses little energy

Air Seasoning- Disadvantages

Disadvantage of Air Seasoning• It takes much longer than kiln seasoning• Large area of space reqired for a lot of

wood• it is notable to produce timber not dry

enough for use in the dry, centrally heated air of modern buildings

Kiln Seasoning• In this method the wooden pieces are kept on

huge trolleys and then it is placed inside the hot chamber of a furnace known as kiln. In this way wooden pieces are kept in a controlled atmospheric conditions for two weeks. The time depends upon the type of wood and initial moisture content. Blowers are also used. It is a quick drying method and the moisture is reduced to 10%. Since seasoning is done at a lesser time through artificial means so the quality of wood is inferior in comparison to seasoned wood through natural seasoning.

Kiln Seasoning

Kiln seasoning

Kiln seasoning

Advantages of Kiln Seasoning• It is dries quickly• It can be controlled• Achieve a lower moisture content• Defects associated with drying can be

controlled

Kiln seasoning

Disadvantage of Kiln Seasoning• It is an expensive method• Requires supervision by a skilled operator• Uses a lot of energy

summary