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 Builders
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.Wood Defects and Blemishes
Patch of bark over which the tree has grown, and has entirely or almost entirely
Separation along the lengthwise grain, caused by too rapid or nonuniform drying
Grain does not run parallel to or spiral around the lengthwise axis
Deterioration caused by various fungi
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
Deposit of solid or liquid pitch enclosed in the wood
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
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
Twist or curve caused by shrinkage that develops in a once flat or straight board
A blemish caused by a mold fungus; it does not weaken the wood