624 



Yearboo\ of Agriculture 1949 



pentachlorophenol, that are soluble in 

 volatile oils, when they are so used, pro- 

 vide clean, odorless, readily paintable, 

 treated wood suitable for interior or 

 exterior use. 



Many proprietary preservatives of 

 undisclosed composition are on the 

 market. Some of them are good, but 

 others have little value. A good pre- 

 caution to take before accepting any 

 proprietary preservative is to have the 

 manufacturer state the ingredients 

 used in his products. 



PREPARING THE WOOD FOR TREAT- 

 MENT is necessary for satisfactory re- 

 sults with any treating process. 



In a few methods the wood is treated 

 green and sometimes with the bark on, 

 but usually it should be well peeled, 

 and, for best results with most proc- 

 esses, seasoned. Because preservatives 

 will not make weak timber strong or 

 restore the strength of timber that has 

 been partly destroyed by decay, only 

 sound timber should be used. The cut- 

 ting, boring, and framing of the wood 

 should be completed before treatment, 

 if possible, to avoid the exposure of 

 untreated surfaces that often results 

 when cutting is delayed until after the 

 treatment. 



Wood is treated by both pressure 

 or nonpressure processes, although the 

 bulk of wood treated is given a pres- 

 sure treatment. For most uses, wood 

 that has been treated under pressure 

 gives the best service. Such treatments 

 require closed cylinders with vacuum, 

 pressure, and heating facilities. 



A number of pressure processes dif- 

 fer from one another in a few details, 

 but the general principle is the same in 

 all. The wood, placed on steel cars, is 

 run into a long steel cylinder, which is 

 then tightly closed and filled with pre- 

 servative. The wood may be steamed 

 or otherwise heated to reduce its mois- 

 ture content and be subjected either 

 to a vacuum or to an initial air pres- 

 sure before the preservative is admitted 

 to the cylinder. By a proper use of pres- 

 sure and heat, the preservative is 

 forced into the wood until it has ab- 



sorbed the desired amount. In most 

 kinds of wood, this results in a rela- 

 tively deep penetration. This treat- 

 ment, when properly made with a good 

 preservative, should add from 20 to 30 

 years to the life of untreated wood for 

 most uses. About 200 pressure-treating 

 plants are in operation at various 

 points in the United States. 



Of the nonpressure methods, the 

 hot-and-cold bath method is the most 

 effective. It involves less equipment 

 than pressure processes and is better 

 adapted to the small commercial and 

 home-use treatments, such as those 

 recommended for fence posts. This 

 method requires either one or two open 

 treating tanks. In the one-tank method, 

 the wood is first heated and then cooled 

 in the same treating solution. The 

 wood may also be heated in air, steam, 

 or other media, and then placed in the 

 tank of cold preservative. In the two- 

 tank process, the wood is heated in a 

 tank of hot preservative and then 

 quickly transferred to the other tank, 

 where it is submerged in cold preserva- 

 tive and allowed to cool. In all cases 

 the heating and subsequent cooling 

 creates a partial vacuum within the 

 wood that aids penetration of the pre- 

 servative. The treatment, when prop- 

 erly made with a good preservative, 

 should increase the serviceable life of 

 the wood by many years. With equal 

 penetration and absorption of the pre- 

 servative, pressure- and nonpressure- 

 treated wood should be equal in 

 serviceability. 



Other nonpressure methods of more 

 recent development are the cold-soak- 

 ing of seasoned timbers in oil solutions 

 of pentachlorophenol and other oil- 

 soluble preservatives and the steeping 

 of green or freshly cut timbers in water- 

 borne preservatives. A single tank or 

 container for the preservative is suffi- 

 cient, but soaking treatments usually 

 require a longer period to get the wood 

 well-treated than when the hot-and- 

 cold bath process is employed. When 

 thoroughly done, these soaking meth- 

 ods add appreciably to the serviceable 

 life of wood. 



