HEAVY TIMBER 



portance that consideration be given to the relation between sap 

 percentage of timbers and the kind of use to which a mill con- 

 struction building is to be put. Where low or average humidity 

 is to be expected, timbers having 85% heart will usually give 

 splendid service ; and where the humidity is higher, the timbers 

 should either be all heart or, in case sapwood is used, such tim- 

 bers should be preserved either with a good quality of coal- 

 tar creosote or, where this for various reasons may be objec- 

 tionable, either with corrosive sublimate (usually known as 

 the Kyanizing process) or with zinc chloride (usually known 

 as the Burnettizing process). /The presence of unlimited 

 amounts of sapwood on timbers, which are to be used in build- 

 ings with high humiditjr, is strongly condemned. No amount 

 of superficial painting with preservatives will be of any value. 



Where untreated timbers are used, it will frequently be 

 found advantageous to paint the ends and bearing surface of 

 any timbers where they come in contact either with other tim- 

 bers, with stone walls, metal or concrete surfaces. In such 

 cases a high grade quality of distillate coal-tar creosote should 

 be employed. 



In the general selection of kinds of timber, yellow pine and 

 Douglas fir will be usually specified for the stress bearing mem- 

 bers such as girders and posts, this selection being based on the 

 availability, suitability and cost of these woods. Consideration 

 should also be given to white, Norway and Western pine, hem- 

 lock, tamarack, spruce and oak where they meet the require- 

 ments. 



For flooring, roofing plank, trim and material where 

 strength is not required, and low or medium humidity in the 

 building does not demand special durability, a wider latitude 

 in the selection is possible. 



Page fifty 



