Impregnation with creosote.
The impregnation of fence posts with creosote is best accomplished by the so-called " open-tank " process, so designated to distinguish it from the "closed " or " pressure " cylinder process which is often employed in creosoting ties and piling. This consists of heating wood for a certain period and then cooling it in the preservative. The principle is simple: during the heating the high temperature causes the air and water contained in the wood cells to expand, so that a portion of this air and water is forced out. The rest contracts as the subsequent cooling progresses, and a partial vacuum is formed, into which atmospheric pressure forces the cool preservative.
The open-tank principle may be variously applied in the treatment of posts. The best way to heat the posts is to immerse their butts in creosote maintained at a temperature of 220° F. If a single tank is used, the cooling bath may be given by permitting the temperature to fall, and in this case the preservative must, of course, be used for the hot bath. It is better, however, to employ an additional tank containing the cold preservative. If two tanks are used and a thorough impregnation of the top of the post is desired, the cold-bath tank should be large enough to permit the soaking of the entire post. The top of the post will not be too heavily impregnated, because it has not been immersed in the hot oil. With two tanks, crude petroleum or any heavy (high-boiling) oil may be used in the hot-bath tank. Creosote is usually the most satisfactory preservative.
Wood used on the farm in various forms other than post material may often be advantageously preserved from decay by chemical treatment, as all timbers used in foundations, sills, beams, and planking, as well as the lower parts of board fences, and the lumber used near the ground in sheds and barns. The treatment of these is very similar to that given posts.
Prolonging the life of shingles (Willis). Water absorbed during a storm subsequently evaporates rapidly from the upper surface of shingles and rather slowly from the lower surface. Consequently, the upper part of the shingle shrinks more than does the under, and curling or warping results. The importance of excluding moisture is obvious. In addition to this, it is advisable to employ an antiseptic to retard decay. The best preservative, it follows, must possess such qualities as will operate in both these ways to prolong the life of the shingles. Apply preservatives only when the wood is thoroughly dry.
Non-antiseptic preservatives. — The application of paint is the preservative measure most commonly used with shingles. The method of applying it. is of paramount importance. Dipping the shingles individually is the only satisfactory procedure. When a roof is painted ridges of paint are formed at the base of the shingles, owing to the irregularities of the surface over which the brush passes. These cause the water to permeate the crevices between the shingles and frequently hasten decay.
Antiseptic preservatives. - The best antiseptics for shingle treatment are creosote and other derivatives of coal tar. Painting the roof with these oils is a rather satisfactory method of treatment, since the coal-tar derivatives penetrate the shingles better than ordinary paint and do not leave ridges below the base of the shingles. At least two coats should be applied. Dipping the individual shingles gives good results. The best results, however, are obtained by heating and cooling the wood in the preservative, as described for the treatment of fence posts.
Suggestions for community action (Willis).
It is often difficult for a farmer efficiently to treat his own material with preservatives. This, however, does not indicate that the work should be neglected. Rather it points to some different means of securing the desired result.
There are two practical methods of doing this. One is for some individual to undertake the work for the neighborhood. A small wood-preserving plant could be profitably operated in connection with a threshing outfit, a feed mill, or sawmill. The other plan is for several farmers to cooperate in establishing and operating the plant. As an indication of the success which should attend such an undertaking, the cooperative creameries of various sections of the country may be cited.