Preservation of Timber
From fungi Preservation of timber means protecting timber and insects attack so that its life is increased. Timber is to be seasoned well before application of preservatives. Widely used preservatives are following:
A. Tar
B. Paints
C. Chemical salt
D. Creosote
E. ASCO
1. Tar: with brush ,hot coal tar is applied to timber. From the attack of fungi and insects, the coating of tar protects the timber. It is a cheapest way of protecting timber. Main disadvantage of this technique of preservation is that appearance is not good after tar is applied it is impossible to apply other attractive paints. Therefore tarring is made only for the unimportant structures such as fence poles.
2. Paints: on clean surface of wood Two to three coats of oil paints are applied. From moisture, the paint protects the timber. From time to time the paint is to be applied. Paint improves the appearance of the timber. Thus lignum paint is a special paint which protects the timber from the attack of termites.
3. Chemical salt: These are the preservatives made in water by dissolving salts. The salts used are, masonry chloride, copper sulphate zinc chloride and sodium fluoride. Salt paints and varnishes can be applied to get good appearance after treating the timber with these chemical.
4. Creosote: by distillation of coal tar, Creosote oil is obtained .The seasoned timber is kept in an air tight chamber and air get exhausted. Then At a pressure of 0.8 to 1.0 N/mm2 and at a temperature of 50°C creosote oil is pumped into the chamber. timber is taken out of the chamber after 1 to 2 hours.
5. ASCO: by the Forest Research Institute, this preservative is developed, Dehradun. It consists of 3 parts by weight of copper sulphate, 1 part by weight of hydrated arsenic pentoxide (As2O5, 2 H2O),(CuSO4⋅5 H2O) and 4 parts by weight of po,tassium dichromate (K2Cr2O7) or sodiudichromate(Na2Cr2O7⋅2 H2O). This particular preservative is available in powder form. With 100 parts of water, by mixing six parts of this powder the solution is prepared. The solution is then sprayed over the surface of timber.
From termites this treatment prevents attack. The surface can be painted to get desired appearance.