1. Collection and preparation of samples:
Timber of nineteen lesser used or unused species of Bangladesh were collected from forests of Chittagong Hill Tracts and got identified in the Bangladesh Forest Research Institute. From heart wood of the each species 10 test samples for natural durability and 25 samples for treatability study were made. The timbers were kiln dried to EMC condition before conversion into test samples. The sizes of samples were 2.5 cm x 5 cm x 50 cm for natural durability and 10 cm x 10 cm x 20 cm for treatability study. The samples were made from clear heart wood and were free from knots, stain, decay, insect hole or other deform ity or defects.
2. Determination of physical properties :
The moisture content and the specific gravity of samples were determined using standard methods.
3. Natural durability test :
The stakes were buried to their half length in the ground of the Forest Res earch Institute’s stake yard. They were buried at 10 cm apart in a row and 30 cm between rows. The stakes were inspected at least four times a year. The process of recording data was continued till the stakes were completely destroyed.
4. Preparation of preservative solution :
i) Water -borne Preservatives; Sample of each species were treated with 10% (2.2:1) CCB solution. The chemicals i.e. copper sulphate, sodium dichromate and boric acid were all commercial grade (95% purity) collected and mixed locally tomeet the standard individual salt component of W/W 40% sodium dichromate, 40% copper sulphate and 20% boric acid equivalent to W/W 45.33% CrO3, 21.33% CaO and 33.33% H3BO3(Anon. 1991). The concentration of the solution were checked by Hydrometer.
ii)Oil -borne Preservatives :
A mixture of creosote and light diesel oil in the ratio of 50: 50 was used as a preservative in this study. Sufficient quantity of this mixture was made and stored in the Rueping tank of the treating plant and then surged for several hours for thorough mixing. Before each charge, the preservation was prehandled in the Rueping tank to about 850c with a view to maintain its temperature at 820c after it was transferred to the treating cylinder.
5.Preservative treatment :
Samples of each species were treated by 10% CCB solution by employing following schedule.
Pressure : 10 Kg / sq cm,
Treatment time : 120 minute.
Samples of each species were treated with 50:50 creosote light diesel oil mixture by Lowry empty cell process of pressure treatment employing following schedule.
Temperature : 800c
Pressure : 10 Kg / Sq. cm.
Treatment time : 120 minutes
Analysis :
After treatment the treated samples were cut crosswise and lengthwise to measure the side and end penetration. The extent of penetration of preservative inside the timber was measured by chemical test. The absorption and retention of the preservative solution through the samples were measured.