TREATING POSTS AND SHINGLES 209 



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 impreg- 

 nation 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 im- 

 mersed 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. 



Other wood. 



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 plank- 

 ing, 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 impor- 

 tance of excluding moisture is obvious. In addition to this, it is 

 advisable to employ an antiseptic to retard decay. The best pre- 

 servative, it follows, must possess such qualities as will operate in 

 both these ways to prolong the life of the shingles. Apply preserv- 

 atives only when the wood is thoroughly dry. 



Non-antiseptic preservatives. — The application of paint is the pre- 

 servative 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. 



