56 BULLETIN 801^ U. S. DEPARTMENT OF AGEICULTUKE. 



should be done before the tin is applied, or preferably before the 

 lumber is nailed together. 



In addition to the preventive methods and care described, pre- 

 servative treatment should be used when trying conditions of 

 humidity or poor ventilation have to be met. Discussion in some 

 detail of such treatment is contained in various bulletins prepared 

 by the Forest Service.^ 



Checking decay already in progress in a building is done best by 

 removing permanently all timbers affected noticeably and then sub- 

 jecting the building to the process of heating and ventilating previ- 

 ously described. Constant ventilation of the ends of timbers should 

 be assured. 



In addition to the strictly preservative treatment described, the 

 application of oil paint to exposed woodwork is valuable. However, 

 no effort should be made to paint wood already treated with creosote, 

 as paint will not adhere to such surfaces. No' paint or other surface 

 applications should be made until lumber is dry and heavy timbers 

 should not be painted for a year after cutting. Paint applied to par- 

 tially green lumber serves to retain the moisture and is conducive to 

 rapid decay. 



Fire-retarclant treatilient for wood has not been developed on a 

 commercial scale applicable to the warehouse. The only practical 

 methods of increasing the resistance to fire offered by this wood con- 

 struction is a surface application of whitewash or a water paint of 

 similar character, or a few other paints carrying chemicals of fire- 

 retardant properties. The most effective of these are limited to 

 interior use,. No such treatment can be relied upon to retard the 

 spread of a hot fire.^ 



Information on the subject of yard piling and seasoning of Inmber is con- 

 tained in Bulletin No. 552 of the IT. S. Department of Agriculture: The 

 Seasoning of Wood, 1917. 



A very fine discussion on Dry Rot in Factory Timbers is issued by the In- 

 spection Department, Associated Factory Mutual Fire Insurance Companies, 31 

 Milk Street, Boston. 



^ See IT. S. Department of Agriculture Bulletins No. 101 : Relative Resistance 

 of Various Conifers to Injection with Creosote ; No. 606 : Relative Resistance of 

 Various Hardwoods to Injection with Creosote ; No. 145 : Tests of Wood Pre- 

 servatives ; No. 286: Strength Tests of Structural Timbers Treated by Commer- 

 cial Wood-Preserving Processes. 



^ Below is a satisfactory formula for whitewash for interior use. For exterior 

 use the glue and rice should be omitted and it should be remembered that no 

 whitewash is really satisfactory when exposed to weather. 



Slake one-half bushel of unslaked lime with boiling water, keeping it covered 

 during the process ; strain it and add a peck of salt dissolved in warm water ; 

 8 pounds of ground rice, put in boiling water and boiled to a thin paste ; one- 

 half pound povv'dered Spanish v\'hiting and a pound of clear glue dissolved in hot 

 water ; mix these well together and let the mixture stand for several days. 

 Keep the wash thus prepared in a kettle or portable furnace, and when used 

 put it on as hot as possible with painter's or whitewash brushes. 



