WHAT ARE THE DIFFERENT TREATMENT PROCESSES OF TIMBER ( IS: 401 ) ?

TREATMENT OF TIMBER 

According to the IS code recommendation the timber treatment are as follows :

   

SURFACE TREATMENT

Surface treatment is done either by spraying, dipping or by brushing the preservative for a short period on thoroughly debarked timber. For the oil type preservatives, the moisture content in timber should not be more than 14 per cent. With water soluble preservatives, a moisture content of 20 to 30 per cent is permissible. At least two coats should be applied. The second and subsequent coats should not be applied until the first one has dried or soaked into the wood. Where possible, the treatment is done hot. Surface treatment is used mostly for treating timber at site and for re-treatment of cut surfaces.

SOAKING TREATMENT 

Soaking treatment consists in submerging debarked timber in the preservative solution for a sufficiently long period until the required absorption of the preservative is obtained. For dry vineers 15 to 30 minutes of soaking are enough.

HOT AND COLD PROCESS

Hot and cold process ensures sterilisation against fungi and insects. The timber is submerged in the preservative solution. Which is then heated to about 90° to 95°C and maintained at this temperature for a suitable period depending on the charge. It is then allowed to cool until the required absorption is obtained. During the heating period, the air in the timber expands and is partially expelled. While cooling, the residual air in the timber contracts and creates a partial vacuum which causes the preservative to be sucked into the timber. Generally two baths are used, the first containing water where the hot treatment is given and the second the cold bath containing the preservatives into which the timber is transferred immediately after heating. This overcomes the danger of precipitation of chemicals at high temperatures. This arrangement also helps to make the process continuous in case the quantity of timber is large.

BOUCHIRIE PROCESS

Sapwood of almost all green timbers with the bark on and of bamboos in green condition, soon after felling, can be treated using any of the inorganic water soluble preservatives by this process. The log of wood attached to the hose pipe and connected to the reservoir containing preservative at an air pressure of 0.1–0.2 N/mm2 on its surface. Due to hydrostatic pressure, the preservative displaces the sap in the wood. The treatment is stopped when the concentration of preservative at the lower end of the log is the same as that in the reservoir.

EMPTY CELL PROCESS

Empty cell process are also known as pressure processes and are aimed at a maximum penetration of the preservative with a minimum net retention. The Lawry process and theRueping process are commonly used

DEFUSION PROCESS

The diffusion process is a method of treatment of timber (poles and planks) and other plant material like bamboos, canes, palm leaves, veneers etc., in green condition. It lends itself best in the case of timbers which are not easy to impregnate under pressure in dry  condition, and also, where there is danger of timber getting deteriorated during seasoning, particularly if air-seasoning is adopted. It may be employed in any of the following manners 

• Momentary dipping in concentrated solution and then close stacking under cover. For refractory veneers over 1.6 mm, 15 minutes soaking and 1 to 2 hours stacking is necessary. It is essential that the glue used for subsequent bonding is compatible with the preservative.

• Prolonged immersion in dilute solution and then close stacking under cover.

• Application of a paste of the preservative over all the surfaces of the timber and then close stacking under cover. This is specially recommended for treatment of refractory species like fir generally used as railway sleepers.

• Injecting the paste into timber through incisions interspread on the surfaces of timber.