632 



Yearbook^ of Agriculture 1949 



be kept from entering through the ends 

 of the logs and spots where the bark 

 has been knocked off by prompt spray- 

 ing or brushing of the exposed wood 

 with solutions containing organic mer- 

 cury salts or chlorophenols or phenates. 



In warm weather, lumber of many 

 species, if not kiln-dried or quickly air- 

 dried, is commonly stained by fungi 

 within a few days after it is sawed. This 

 can be controlled by dipping the lum- 

 ber in a toxic solution not more than 24 

 hours after sawing. The same fungi- 

 cides are used as for logs, but at lower 

 strengths ; the cost for materials is only 

 15 to 20 cents a thousand board feet 

 of lumber dipped. Such dipping, if fol- 

 lowed by good open piling to dry the 

 lumber, reduces to a minimum the 

 molding and staining and also the de- 

 cay that sometimes gets started during 

 seasoning. 



To prevent decay in storage or use, 

 the most generally practicable method 

 is to keep the wood dry all the time or 

 for so much of it that decay fungi never 

 have a chance to get started. Until 

 lumber is dry, it should not be solid- 

 piled or built into parts of structures in 

 which further drying is slow, unless it 

 has been dipped promptly after saw- 

 ing in a stain-control chemical solution. 



To avoid decay in buildings, roof 

 leaks must be avoided. Exterior walls 

 must be so constructed that there is a 

 minimum chance for water to enter at 

 joints and be trapped in the wall. 

 Where wood is on concrete laid on soil, 

 there should be a dampproofing layer 

 in or on the concrete; all embedded 

 stringers should be of a decay-resistant 

 wood or impregnated with a preserva- 

 tive. 



Buildings without basements are 

 subject to a special decay risk. During 

 cold weather, moisture evaporating 

 from the soil under the building may 

 condense on the cold surface of the 

 sills and joists, and stay long enough to 

 let decay fungi get started. This sweat- 

 ing can be prevented by placing venti- 

 lating openings in the foundation wall 

 on opposite sides of the building. Under 

 test buildings where the vents have 



been too few or too small to keep the 

 wood dry, the moist condition has been 

 relieved by simply laying a cover on 

 the soil under the building. Heavy roll 

 roofing (55 Ibs. or more per 108 square 

 feet) rolled out on the soil and lapped 

 but not fastened, was very effective. A 

 3-inch layer of slag or gravel in the 

 soil, though apparently somewhat less 

 efficient, was also helpful. 



Where wood must be used in con- 

 tact with soil or water, it should be 

 either heartwood of one of the highly 

 durable species or else it should be 

 impregnated with a good preservative. 

 Even in the best species, the heartwood 

 from young trees or from the central 

 heart of old trees is likely to be rather 

 decay-susceptible. No sapwood of any 

 species should be used in contact with 

 soil without thorough preservative 

 impregnation. Treatment of sills and 

 first-floor joists of low buildings is a 

 desirable although not a necessary 

 precaution. 



Impregnation is best accomplished 

 by pressure treatment at a commercial 

 treating plant. Wood of ordinary lum- 

 ber thickness can be reasonably well 

 impregnated without pressure if given 

 a hot bath followed by a cold bath. 

 Dip or brush treatments have some 

 place in wood members exposed to 

 rain or occasional moisture, as in 

 porches and window sash and frames, 

 if it is too difficult to get impregnated 

 lumber locally. Water and fungi enter 

 through exposed end grain more 

 readily than through sides; preserva- 

 tive treatment of ends of members is 

 therefore especially profitable. If un- 

 treated ends are exposed, no treatment 

 is worth much. Paint can be of value 

 for decay prevention if it is unusually 

 well maintained, with no cracks at the 

 joints. If wood is painted when green, 

 its drying out may be delayed and the 

 decay hazard actually increased. 



In the special case of boat construc- 

 tion, only heartwood of durable or 

 moderately durable species should be 

 used. These would include the woods 

 mentioned previously; also teak and 

 mahogany ; white or chestnut oak, but 



