c. Termite. Termites are not true ants
1-13. CAUSES OF DECAY
although they look much like them and live like
There are several types of decay which render
them, in large colonies. The winged male and female
lumber unserviceable: dry rot, wet rot, and common
may be seen "swarming" in the spring or fall on their
rot.
way to start new colonies. Otherwise they are very
seldom seen, as they stay in the earth or in wood.
a. Dry rot. Dry rot is the most common
They damage rafters, joists, beams, or other timber of
and the most dangerous. It is a disease which spreads
buildings; the inside may be entirely eaten out before
from one part of the wood to another, causing the
the damage is noticed since termites leave an outer
wood to lose its strength and cohesive power and
shell of wood.
eventually to decay altogether. Dry rot occurs most
often where timber is kept alternately wet and dry, or
d. Marine borer.
where there is no ventilation. The rot occurs on the
inside of timber and leaves a shell on the outside; the
(1) Timber placed in water is subject to
inner part becomes soft and powderlike and is
attack by two classes of marine borers, the mollusk
generally invisible due to the outer shell.
and crustacean type.
b. Wet rot. Wet rot occurs in growing
(2) The destructive mollusk is a worm,
trees and is similar to dry rot. It occurs when the
sometimes called the navalis, teredo, or shipworm. It
wood becomes saturated with water which it absorbs
has a head equipped with a shell-like substance
from a swamp or bog.
It may be readily
shaped like an auger by means of which it bores its
communicated from one piece of wood to another by
way into timber. It has been known to grow to sizes
contact.
of 1/4 to 1/2 inch in diameter and from 1 1/2 to 3 feet
in length. It may ruin timber in less than a year. This
c. Common rot.
Common rot is
marine borer prefers clear salty water. It operates
manifested by the presence of external yellow spots
against timber set between the mean tide and low
on the ends of timber or by a yellowish dust in the
water mark and about a foot above the mud line.
checks and cracks, especially where the pieces are in
contact with one another. This is caused by improper
(3) The wood louse is a member of the
ventilation of wood-storage sheds and lumber piles.
crustacean family. It grows to the size of a grain of
It is easily remedied by proper stacking and
rice and bores into wood by means of sharp jaws. It
ventilation.
is active only in clear still water and confines itself to
a belt or line around the low water line. Wood lice
1-14. DESTRUCTION BY INSECTS
can destroy piling within a year's time in heavily
infested areas.
Although decay is the principal cause of
deterioration, a great deal of damage can be done by
1-15. STANDARD SIZES OF LUMBER
certain insects. The most common land varieties of
destructive insects are the powder post, the pole
Lumber is usually sawed into standard sizes of
borer, and the termite. The most common water type
length, width, and thickness. This permits uniformity
is the marine borer.
in planning structures and in ordering materials.
Table 1-1 list some nominal and minimum-dressed
a. Powder post.
The powder post
sizes for dry, softwood lumber as set forth in the
develops very rapidly. It bores into the wood and
American Softwood Lumber Standard, Voluntary
transforms it into a fine powder. Since the powder
Product Standard 20-70.
Dry lumber, in this
post lodges initially under the bark, all bark should be
instance, is defined as lumber which has been
removed from airdried lumber before it is used in
seasoned to a moisture content of 19 percent or less.
buildings.
Lumber having a moisture content in excess of 19
percent is called green lumber and the dressed
b. Pole borer. The pole borer attacks
dimensions may be slightly
timber that is somewhat damp and transforms it into
reddish-brown dust. It will not attack watersoaked
timber, but it will attack dry timber, either sound or
decayed.
1-17
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