BUILDING CONSTRUCTION 133 



In most building work, particularly in cities, the timber required 

 is procurable from the importer ready cut into the usual commercial 

 sizes. 



DEFECTS IN TIMBER. The defects which should be looked for in 

 timber are various. These defects are natural, and common to 

 all kinds of timber. Such faults should be removed, if possible, 

 during conversion. 



In many classes of work a certain percentage of such defects 

 as are mentioned hereafter is permissible, it being impossible to get 

 perfect timber except at a very great cost. The following are 

 common defects : 



Sapwood. Of the defects in timber, the most serious is the pres- 

 ence of an undue proportion of sapwood. A great deal of sapwood 

 is to be found in timber which is now on the market. This is due 

 to the felling of immature trees. The sapwood is spongy in grain, 

 showing large annual rings, and is generally of a blue colour. The 

 sapwood in a board can be distinguished from the hardwood by the 

 difference in colour. For constructional work or joiner work 

 spongy or open-grained wood should be avoided. Sapwood is very 

 liable to decay, and subject to attack by dry rot. Being immature 

 it lacks strength in comparison with heartwood. 



Shakes. Shakes in timber are cracks due to contraction in the 

 seasoning or drying of the timber. 



Star shakes are due to the shrinkage of the wood on lines 

 parallel to the annual rings. Heart shakes extend through or near 

 to the heart of the tree. Cup shakes are caused by the partial separa- 

 tion of the layers composing the annual rings and are the most 

 objectionable in timber, as they often extend for a considerable 

 distance through the log. Experts can detect cup shakes by sounding 

 the log. In converted timber, that is, timber cut into scantlings, 

 cup shakes are not found in any great number, as in the process of 

 conversion the defective parts of the log are discarded. Star shakes 

 and heart shakes do not usually extend far into the log or batten. 



Knots. Knots in timber are the cross section of branches and 

 shoots. These cannot be avoided, and are particularly numerous 

 in red pine or redwood, less numerous in white pine, and of rare 

 occurrence in good American yellow pine. Timber containing large 

 loose knots should be avoided for structural work, but firm, un- 

 decayed knots, if not excessive in number or too large, are not 

 objectionable. 



Waney Edges. " Waney edges " is a term which refers to a 

 batten or " deal " having a splayed or rather slightly rounded corner 

 or edge. This at once reveals the fact that the particular scantling 



