SPECIFICATION FOR THE PRESERVATION OF TIMBERS ( IS: 401 )

PRESERVATION OF TIMBER :

Preservation of timber means protecting timber from fungi and insects attacks so that its life is increased. One of the basic approaches to protect it is to create conditions unfavourable to fungi. Low humidity, heat and water insulation, etc. help to maintain the timber dry and thus make it insusceptible to damage by fungi. Water absorption, decay and other undesirable effects can be minimized by coating the surface of wood with polymer films or drying oils, oil base paints, varnishes and synthetic enamels.

The following are the widely used preservatives :

1. OIL PRESERVATIVES : 

Oil preservatives are applied over outside of exposed timber, give unpleasant smell and are not suitable when timber is to be painted. The types in use are creosote, carbolinium, solignum etc. with or without admixture with petroleum or suitable oils having a high boiling range.

2. ORGANIC SOLVENT PRESERVATIVES : 

consists of toxic chemical compounds, e.g. pentachlorophenol, benzene-hexa-chloride, dichlorodiphenyltrichloro-ethane (D.D.T) and copper naphthenate. These are dissolved in suitable organic solvents like naphtha, or in petroleum products such as kerosene, spirit, etc. The treated timber can be painted or polished.

Acetic anhydride treatment : is used for protection of veneers, plywood and light lumbers against decay by acetylation. They are treated with acetic anhydride vapour, which minimises swelling and improves resistance to decay and attack by insects.

3. WATER SOLUBLE PRESERVATIVES : 

Water soluble preservatives are odourless organic or inorganic salts and are adopted for inside locations only. If applied over outside surfaces, the salts can be leached by rainwater. Examples of leachable (3A-water soluble) type of preservatives are zinc chloride, boric acid (borax), etc. Zinc chloride, sodium fluoride and sodium-penta-chloro-phenate are toxic to fungi. These are expensive and odourless (except for sodium-penta-chloro-phenate). Benzenehexa- chloride is used as spray against borers. Boric acid is used against Lyctus borers and to protect plywood in tea chests.