TYPES OF TIMBER SEASONING

Two main types of timber seasoning are under

Natural seasoning

It is a very time-consuming process that usually takes 2 to 4 years to make timber fit for the work. In this method seasoning is carried out by natural air hence it is sometimes referred to as Air seasoning. This method is a cheap and simple types of timber seasoning. But natural factors are really difficult to control. Hence, this has become obsolete nowadays.

Artificial seasoning

ELECTRICAL SEASONING:- In the method of electrical seasoning timber is subjected to high-frequency alternate currents. Now and then, the resistance of wood to electricity is measured. When the required resistance is reached seasoning process is stopped because the resistance of timber increases by reducing moisture content in its types of timber seasoning. It is also called rapid seasoning and it is uneconomical.

CHEMICAL SEASONING: – This timber is immersed in a solution of soluble salts such as zinc chloride and mercury chloride which increases the rate of evaporation. In this method evaporation in heart wood is comparatively more than sap wood. Hence sections obtained by this method have a lesser tendency against cracking.

WATER SEASONING:- The technique known as “water seasoning” involves submerging wood in water to help dissolve any sap that may be present. It will take 2-4 weeks and after that timber is allowed to dry. A timber section should be placed such that a larger portion faces upstream and a shorter portion faces downstream. Section obtained by this process has lesser tendency against twisting and warping (due to removal of sap) but is observed to lose its strength.

SEASONING BY BOILING:- Seasoning of timber is also achieved by boiling it in water for 3-4 hours. After boiling timber is allowed to dry naturally. For large quantities of timber, boiling is difficult so, sometimes hot steam is passed through the timber logs in an enclosed room. It also gives good results. Timber obtained by this method is observed to lose its plasticity and strength.

KILN SEASONING:- In this method, timber is subjected to hot air in air air-tight chamber. The moisture content is decreased by the heated air that moves between the logs of wood. Heating coils help to raise the temperature inside the chamber. The temperature inside the chamber is raised with the help of heating coils. When the required temperature is obtained moisture content and relative humidity get reduced and timber gets seasoned. even though It is a costly process, it will give good results strength-wise.

SAWING OF TIMBER

The process of giving the required shape and size to the timber section is termed conversion/sawing of timber.
By sawing timber can be converted into transferable parts.
Various methods of sawing are.

ORDINARY/ FLAT/ SLAB SAWING:-
- parallel cuts made throughout the length of the log i.e. tangential to the annual rings.
- Easiest and most economical method.
- Causing twisting and warping of planks.

QUARTER SAWING:-
- When applied to wood not having distinct medullary rays, this method produces very fine wood.
- In this method saw cuts are made at right angles to each other.
- Tendency to cup i.e. to curve in a transverse direction.

TANGENTIAL SAWING:-
- In this saw, cuts are made tangential to annual rings which meet each other at right angles.
- It is suitable for those sections which have distinct annual rings and indistinct medullary rays.
- Not suitable for flooring.
- Section observed to have the least strength.

RADIAL/ RIFT SAWING:-
- Saw cuts are in a radial direction parallel to medullary rays in this method.
- Wastage of timber is observed to have maximum in this method.
- The section obtained has maximum strength and induces a decorative effect too.

PRESERVATION OF TIMBER

Preservation of timber is carried out to increase its life types of timber seasoning , durability, and resistance against deforming agencies like insects, termites, and fungi etc. various preservatives used are:-

ASCU Treatment:-
- Application of ASCU increases resistance against white ants.
- Consist of 1 part by weight of arsenic pentaoxide (As2O5.2H2O), 3 parts by weight of copper sulphate (CuSO4.5H2O), 4 parts by weight of potassium-di-chromate/ sodiumdichromate(K2Cr2O7/Na2Cr2O7).
- This is available in powder form hence to prepare the solution 6 parts of ASCU are mixed with 100 parts by weight of water.
OIL PAINTS:-
- Oil paints increase resistance against penetration of water thereby increasing its durability.
COAL TAR:-
- Coal tar is heated and liquid hot tar is applied on the timber surface using a brush.
- It increases resistance against fire. However, it decreases the aesthetic value of the structure and also gives an unpleasant odor hence is used for minor engineering works only.
SOLIGNUM PAINTS:-
- this increases resistance against white ants but cost is more than ASCU.
- It also gives a decorative effect to the timber section.
CHEMICAL SALTS:-
- Chemical salts like copper sulfate, mercury chloride, and zinc chloride are used as preservatives which can be dissolved in water to get liquid solution. They are odorless and do not generate flames when in contact with fire.
CREOSOTE OIL FOR PRESERVATION:-
- Creosote oil is prepared by the distillation of tar.
- It is black or brown.
- It contains an unpleasant smell and is applied specially.
- Firstly, the timber is well seasoned and dried, then it is placed in an airtight chamber, and inside air is pumped out. Finally, creosote oil is pumped into the chamber with a high pressure of about 0.7 to 1 N/mm2 at a temperature of 500c.
- After allowing for 2 hours, the timber absorbs creosote oil sufficiently and taken out from chamber.
- It is not used for timber works in fire places because creosote oil is flammable. It is generally used for wood piles, poles and railway sleepers.
- Creosoting is also known as bethel’s process.

METHODS OF TIMBER PRESERVATIONS

Brushing
Spraying
Injecting under pressure
Dipping and stepping
Charring
Hot and cold open tank treatment.
The most effective method of preservation is pressure impregnation in which preservative is injected under pressure.

The sequence of increasing order of effectiveness is

Brushing/spraying < dipping and stepping < hot and cold open tank application < pressure application