2. Seasoning of timber
1. Definition of seasoning
2. Natural seasoning
3. Artificial seasoning
a. Kiln seasoning
b. Chemical seasoning
c. Electrical seasoning
d. Seasoning by boiling
e. Water seasoning
3. What is seasoning?
Seasoning of timber is the process of lowering down the natural
moisture content of timber, seasoning should be planned in
such a way that evaporation of water from the outer layers and
the movement of water from the interior to the outer surface is
balanced. Moisture should be removed at a uniform rate and the
moisture that cannot be removed remains uniformly distributed
throughout the mass as far as possible, irregular drying , setup
internal stresses which may cause defects like warping, shake,
etc
4. Advantages of seasoning:
• Seasoning makes timber resistive against decay due to borers, termites,
fungi etc.
• Reduces weight of timber and hence saves cost of transportation.
• Makes timber stronger, stiff and hard makes timber receptive for paints,
varnishes and preservatives
• Reduce shrinkage of timber
• Makes timber easily workable
• Reduces chances of warping and cracking of timber
• increases resistive power of timber against electricity
• Timber can be easily used as fuel
• Increases durability of timber
5. Preparation of natural seasoning:
• It is not possible to season the timber in log form. Logs are cuts and sawn to suitable
sections.
• Ends of logs or planks should be painted with tar, asphalt, paraffin wax, sealing liquid to
avoid splitting at ends.
• Pillars about 300 mm height and 300 mm square are constructed at about 1200 mm
intervals out of bricks or stone masonry or concrete. Top of all the pillars should be at
same level.
• Long beams of 100mm x 100 mm are placed on the pillars, to form framework for
stacking timber.
• Timber pieces are assembled and arranged in layers one above the other. All pieces in one
layer should have same thickness to avoid changes to warping or cracking.
• Stacks should be protected from rain, wind heat of sun. a roof of suitable material should
be provided at the top.
6. Advantages
• Requires minimum supervision
• Economical
• Suitable for thick as well as thin
sections.
Draw backs
• Process is slow. Takes 1 to 4 for seasoning.
• No control over natural air.
• Moisture content can not be brought to
desired level
• Drying is not uniform
• More space is required.
7.
8. There are two main types of kiln used in artificial seasoning
Compartmental kilns
Progressive kiln
Both methods rely on the controlled environment to dry out the timber
and require the following factors :
Forced air circulation by using large fans, blowers, etc.
Heat provided b piped steam
Humidity control provided by steam jets
The amount and duration of air, heat and humidity again depends
on species, size, quantity, etc. in general, the atmosphere in the
kiln at first will be cool and moist. The temperature is gradually
increased and the humidity reduced until the required moisture
content is achieved.
Kiln seasoning
9.
10. Chemical seasoning:
It is the preliminary treatment given to the
timber before kiln seasoning. Sodium chloride,
sodium nitrate, urea are used. These chemicals
reduce vapour on the surface of application.
Hence wood surface remains moist while
moisture from inner portion diffuses towards
surface. Timber dries first from inside, hence
chances of cracking are reduced. After
application of chemicals timber is seasoned as
usual.
11. Electrical seasoning:
When high frequency electric current is
passed, through a piece of green timber,
resistance offered by green timber is less. On
drying of timber the resistance increases
which generates more heat. Timber pieces
are dried quickly. This process consumes
more electricity, requires costly equipment
and reduces strength of wood. It is not
economical.
