Preservation of timber is carried out in order to increase its life, durability, and resistance against deforming agencies like insects, termite, and fungi, etc. various preservatives. Preservation of timber is done using different types of preservatives. Increasing life makes the timber more durable and it can be used for longer periods. Preservation also helps the timber to get rid of insects and fungi etc.
a) ASCU Treatment:-
ASCU is a special preservative which is available in powder form. It is dissolved in water to get a preservative solution. It should be added 6 parts by weight of ASCU in 100 parts by weight of water. The final solution is applied to timber by spraying. This solution does not contain any odor. It is useful mainly to get rid of white ants.
- The 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 sulfate (CuSO4.5H2O), 4 parts by weight of potassium-di-chromate/ sodium –di-chromate(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.
b) OIL PAINTS:-
- Oil paints increase resistance against penetration of water thereby increases its durability.
c) COAL TAR:-
Coal tar contains the unpleasant smell and does not allow the paint on it. So, it is used for door frames, window frames, etc. It is very cheap and has good fire resistance.
- Coal tar is heated and obtained liquid hot tar is applied on the timber surface using a brush.
- It increases resistance against fire. But it decreases the aesthetic value of the structure and also gives unpleasant odor hence is used for minor engineering works only.
d) SOLIGNUM PAINTS:-
- this increases resistance against white ants but the cost is more than ASCU.
- It also gives a decorative effect to the timber section.
e) CHEMICAL SALTS:-
- Chemical salts like copper sulfate, mercury chloride, and zinc chloride are used as a preservative which can be dissolved in water to get a liquid solution. They are odorless and do not generate flames when contact with fire.
f) CREOSOTE OIL FOR PRESERVATION:-
- Creosote oil is prepared by the distillation of tar.
- It is black or brown in color.
- It contains unpleasant smells and applied in a special manner.
- 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 high pressure 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 the chamber.
- It is not used for timber works in fireplaces 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 Preservation Of Timber:-
- Brushing:- Brushings the simplest method of applying preservatives. For well-seasoned timber, oil type preservatives are applied.
- Spraying:- Spraying is time-saving and quite effective it is an effective technique than brushing. In this case, the preservative solution is sprayed on to the surface using a spray gun.
- Injecting under pressure:- It is a costly treatment process and required special treatment plants. The preservative is injected into the timber under high-pressure conditions. Generally, creosote oil is applied in it.
- Dipping and stepping:- This solution penetrates the timber better than the case of brushing or spraying. Dipping is another type of preserving in which, timber is dipped directly in the preservative solution.
- Hot and cold open tank treatment:- In this method, the timber is placed in an open tank which contains the preservative solution. This solution is then heated for a few hours at 85 to 95 degrees Celsius. Then, the solution is allowed to cool and timber gets submerged with this gradual cooling.
The most effective method of preservation is pressure impregnation in which preservative is injected under pressure.