The Wood for the Job 



619 



board shrink at a faster rate than the 

 remainder of the wood. If, as with 

 encased knots, the knots are not an 

 integral part of the wood, they may 

 become loosened even to the extent of 

 falling out of the board. 



Knots also affect both the appear- 

 ance and the strength of a piece of 

 wood. Except for knotty finish, they are 

 considered objectionable from the 

 standpoint of appearance. They reduce 

 the strength of lumber according to 

 their number, size, quality, and posi- 

 tion in a piece. Strength is reduced 

 more by an intergrown knot than by 

 an encased knot, or even a knot hole, 

 because the wood fibers are more dis- 

 torted. 



Where painting is to be done, wood 

 that contains pitch which is an ac- 

 cumulation of resin in the wood cells 

 should be avoided because it does not 

 easily retain paint or varnish. The 

 select grades of lumber allow only a 

 small amount of pitch. Pitch pockets 

 have a slight weakening effect on lum- 

 ber, but their chief disadvantage is that 

 the liquid pitch sometimes runs out of 

 the board in use. Woods that tend to 

 have pitch pockets can usually be de- 

 tected by visual examination. 



WOOD DETERIORATES in use like any 

 other material. Iron and steel may rust 

 upon exposure; wood may deteriorate 

 through the action of fungi in damp 

 places. The best way to prevent decay 

 in the wood used in homes and farms 

 is to use only dry wood in the original 

 work and to keep it always dry. 



Most of the wood used in homes does 

 not come in contact with moisture 

 enough to cause concern. A number of 

 the danger points, however, call for 

 definite precautions. Wood posts in 

 basements should rest on concrete foot- 

 ings that rise about 3 inches above the 

 flood. The same precautions should be 

 taken where wood stairs rest on the 

 basement floor. Points to watch outside 

 the house include steps, siding, posts, 

 and framework of porches that are in 

 contact with the ground; basement 

 window frames and siding that are near 



drain pipes ; fence posts ; and floors that 

 are laid close to the ground over un- 

 ventilated areas. 



Untreated wood should be kept at 

 least 18 inches above the ground level. 

 When that is not practical, one should 

 use heartwood of a decay-resistant 

 species (sapwood of all species has low 

 decay resistance) or wood that has 

 been given a good preservative treat- 

 ment. Wood that has been pressure- 

 treated with a preservative gives the 

 best service, but the life of fence posts 

 and similar items can be extended by 

 preservative treatment in a bath, a pro- 

 cess the farmer or home owner can do 

 himself. 



Proper care of that kind and proper 

 selection and use will give further evi- 

 dence of the reasons why wood has 

 been one of the foremost building ma- 

 terials for thousands of years. 



R. P. A. JOHNSON was trained in 

 civil engineering at the Virginia Poly- 

 technic Institute. He holds advanced 

 degrees from the University of Wis- 

 consin. He entered the Forest Service 

 in 1908, serving in Montana, Arizona, 

 New Mexico, and Arkansas. He trans- 

 ferred to the Forest Products Labora- 

 tory in 1918 and served in the Division 

 of Industrial Investigations and the Di- 

 vision of Timber Mechanics^ of which 

 he is now the chief. 



CHARLES E. VAN HAGAN was grad- 

 uated from the University of Wisconsin 

 as a civil engineer in 1936. After grad- 

 uate work in transportation at Yale 

 University, he was employed as an 

 engineer by two construction firms and 

 the Wisconsin Highway Department 

 before joining the Forest Products 

 Laboratory as an engineer in 1944. He 

 is the secretary-treasurer of the Forest 

 Products Research Society. 



The last section of this book con- 

 tains more information on the average 

 weights of wood, characteristics and 

 properties) and similar subjects of value 

 to the home owner. Attention is di- 

 rected to the list of some of the Forest 

 Products Laboratory publications. 



