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LUMBER The  terms  "wood"  "lumber,"  and  "timber"  are often spoken of or written in ways to suggest that their meanings are alike or nearly so. But in the Builder’s language, the terms have distinct, separate meanings. Wood is the hard, fibrous substance that forms the major  part  of  the  trunk  and  branches  of  a  tree. Lumber is wood that has been cut and surfaced for use in  construction  work.  Timber  is  lumber  that  is 5 inches or more in both thickness and width. SEASONING OF LUMBER Seasoning  of  lumber  is  the  result  of  removing moisture  from  the  small  and  large  cells  of  wood— drying.  The  advantages  of  seasoning  lumber  are  to reduce  its  weight;  increase  its  strength  and  resistance to  decay;  and  decrease  shrinkage,  which  tends  to avoid  checking  and  warping  after  lumber  is  placed.  A seldom  used  and  rather  slow  method  of  seasoning lumber is air-drying in a shed or stacking in the open until dry. A faster method, known as kiln drying, has lumber placed in a large oven or kiln and dried with heat, supplied by gas- or oil-fired burners. Lumber is considered dry enough for most uses when its moisture content has been reduced to about 12 or 15 percent. As a Builder, you will learn to judge the dryness of lumber by  its  color,  weight,  smell,  and  feel.  Also,  after  the lumber is cut, you will be able to judge the moisture content by looking at the shavings and chips. DEFECTS  AND  BLEMISHES A defect in lumber is any flaw that tends to affect the strength, durability, or utility value of the lumber. A blemish is a flaw that mars only the appearance of lumber.  However,  a  blemish  that  affects  the  utility value of lumber is also considered to be a defect; for example,  a  tight  knot  that  mars  the  appearance  of lumber  intended  for  fine  cabinet  work. Various  flaws  apparent  in  lumber  are  listed  in table 3-2. Table 3-2.—Wood Defects and Blemishes COMMON  NAME DESCRIPTION Bark  Pocket Patch of bark over which the tree has grown, and has entirely or almost entirely enclosed Check Separation  along  the  lengthwise  grain,  caused  by  too  rapid  or  nonuniform  drying Cross  Grain Grain does not run parallel to or spiral around the lengthwise axis Decay Deterioration  caused  by  various  fungi Knot Root section of a branch that may appear on a surface in cross section or lengthwise. A cross-sectional knot maybe loose or tight. A lengthwise knot is called a spike knot Pitch Pocket Deposit of solid or liquid pitch enclosed in the wood Shake Separation along the lengthwise grain that exists before the tree is cut. A heart shake moves outward from the center of the tree and is caused by decay at the center of the trunk. A wind shake follows the circular lines of the annual rings; its cause is not definitely   known Wane Flaw in an edge or corner of a board or timber. It is caused by the presence of bark or lack of wood in that part Warp Twist or curve caused by shrinkage that develops in a once flat or straight board Blue Stain A blemish caused by a mold fungus; it does not weaken the wood 3-25



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