List and explain any THREE methods used in applying preservatives – NABTEB QUESTION

(i) Application by hand brush/spray gun.
(ii) By dipping
(iii) By steeping

(i) Application by hand brush/spray gun preservatives is commonly applied by brush and spray gun. The preservatives should be liberally applied and any shakes or cracks in the surface should be filled. Two or three coats are necessary and each coat should be allowed to dry before the next is applied.

(ii) By dipping: This is the submerging of timber in a preservative tank for a short time. The size of the tank is governed by the size and shapes of timber units to be dipped. After the timbers are dipped, the units are placed on a draining rack. Usually of corrugated sheets to drain off.

(iii) Steeping: This method of applying preservatives consists of submerging timber in a tank of either hot or cold preservatives for a period of two or four hours. Dipping and steeping methods are more effective than application by hand brush. When seasoned timber are placed in a tank and held in position with bars, cold creosote is run into the tank to cover up the timber and is gradually heated to 94°C. After being maintained at this temperature for one hour or three hours, the heat is turned off and the preservative is allowed to cool. The liquid is then pumped back to the storage tank and the timber removed.