Preservative Treatment of Wood 



623 



that are heated sufficiently to reduce 

 the relative humidity. 



RAYMOND C. RIETZ was trained in 

 economics and mechanical engineering 

 in Beloit College and the University 

 of Wisconsin. He was employed by a 

 producer of southern hardwood lum- 

 ber in central Mississippi before he 

 joined the Forest Products Laboratory 



in 1928. During the Second World 

 War he was assistant to the chief of 

 the Division of Materiel Containers. 

 He directs research in the seasoning 

 and physical properties of wood as 

 chief of the Division of Timber Physics 

 in the Laboratory. He has written sev- 

 eral articles on the seasoning of wood, 

 and has developed a method of kiln 

 drying pine cones for seed extraction. 



PRESERVATIVE TREATMENT OF WOOD 



THOMAS R. TRUAX 



Wood now in useful service is being 

 destroyed in this country by decay and 

 insects at the rate of several billion 

 board feet a year an amount ap- 

 proaching the normal average used an- 

 nually in the construction of dwelling 

 units. The enormous drain upon the 

 resources of our forests can be lessened 

 through greater use of preservative- 

 treated wood, one piece of which may 

 do the work of several replacements of 

 untreated wood. 



The railroads long ago found that 

 preservative treatments save wood and 

 money. In the early days when most 

 railroad ties were untreated, railroads 

 required for replacements each year 

 approximately 450 ties to the mile; in 

 recent years when a large percentage 

 of all ties in service were treated, they 

 required less than one-third as many re- 

 placements to the mile. The same order 

 of savings also applies to telegraph and 

 telephone poles and to poles for other 

 public-utility lines. Ninety percent of 

 all poles now being set in the ground 

 are either fully treated or butt- treated. 



Many other wood products that are 

 exposed to decay and insect attack are 

 not so extensively treated. For ex- 

 ample, a large part of the 600 million 

 fence posts set yearly are not treated, 

 although it has been shown that many 

 species of wood in post size will last 

 from 3 to 10 times as long when well- 

 treated as when untreated. The service- 

 able life of still other products would 



be increased by preservative treat- 

 ments. 



The type of preservative used and 

 the thoroughness with which the wood 

 is treated have much to do with the 

 length of service rendered by the wood. 

 Good preservatives and poor treat- 

 ments or poor preservatives and good 

 treatments are of little value. The pur- 

 pose of treating wood with preserva- 

 tives is to protect it against decay 

 organisms, insects, and marine borers. 



Preservatives of various kinds are 

 used to treat various classes of wood 

 products. 



Among the wood-preserving oils, 

 coal-tar creosote has long been effec- 

 tive. It has good penetrating proper- 

 ties and will remain in the wood for 

 many years ; it is safe to handle, harm- 

 less to wood and metal, readily avail- 

 able, and reasonably cheap. It is used 

 mainly on wood that is to be in contact 

 with the soil and water out of doors, 

 and where its odor will be unobjection- 

 able and painting will be unnecessary. 



For wood that is used indoors or not 

 in contact with the ground or water 

 outdoors, water-borne preservatives 

 are usually favored. Among these are 

 zinc chloride, chromated zinc chloride, 

 and several proprietary preservatives 

 consisting of various mixtures of com- 

 pounds of arsenic, chromium, copper, 

 or fluorine, all of which leave the wood 

 in a paintable condition. 



Still other preservatives, such as 



