188 FOREST UTILIZATION TIMBER PRESERVATION 



treatment, and therefore thorough penetration is obtained on posts 

 and poles where the preservative is most needed. Open-tank treat- 

 ment is conducted in a very simple and inexpensive manner. Old 

 tanks, metal barrels, or other containers are used for the process. Fires 

 are built underneath them to heat the creosote to the proper tempera- 

 ture and nearby containers are used in which the posts and poles are 

 plunged. 



Brush or spray treatment consists of using creosote, paint, or other 



FIG. 98. Many thousands of fence posts are annually treated with creosote to 



increase their length of life in service. This treating plant is on the San Juan 



National Forest, Colorado. Many miles of drift fences are built to control 



grazing on the National Forests. 



materials to treat the wood superficially. This method is used with 

 poles, posts, shingles, timbers, and many other forest products. Many 

 patented preservatives are on the market for use in connection with 

 the brush or spray treatment. Although not so effective as the press- 

 ure or open-tank methods of treatment, satisfactory results are often 

 obtained by this means. All the cracks and checks are completely 

 filled or covered with the fluid. Knot holes or similar defects offer 

 the best opening for wood-destroying fungi. All wood should be 

 thoroughly air seasoned before brush or spray treatment. Dipping is 

 another method of treatment and sometimes yields satisfactory results 

 with piles, caps, and other timber as well as with shingles, posts, and 

 some poles. 



