AII-SEASONING AIICICAFT STOCK
Ievised, September 1944
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TillS IREPORIT IS ONE 0f A SE[IIES ISSUED)
TO All)D TIME NATION'S WAR EIfFORT
UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST PRODUCTS LABORATORY
In Cooperation with the University of Wisconsin
AI? SUASC::IYG AIRCRAFT STOCK1
It may be necessary to carry a surplus stock of lumber to insure
a..air.st shortage at the time of manufacture. If the stock is green, advan-
tate may be taken of this intermediate period to reduce the moisture content,
tCreby reducing the time required for kiln drying,
Lumber properly seasoned should be of uniform moisture content,
strai.jht, free from stain or decay, and without end or surface checks. Ob-
serva'.ce of the following rules will help to secure the desired results:
(a) S~ain prevention:
If stain is likely to occur, freshly cut lumber containing
sapwood should be dipped in or sprayed with an antiseptic solution
to protect it against attack by fungi during the air-seasoning
(b) Foundations for lumber piles:
(1) Foundations should be rigid and properly leveled.
(3) Foundations should be high enough from the ground
to allow good circulation. The minimum. distance that lumber
should be from the ground at the rear of the pile is 18 inches,
(3) Foundations should slope from front to rear about
1 inch to t.he foot.
(4) M"aterial for piers is listed in order of durability
and should be so selected whenever available:
Pressure-creosoted blocks of any species or the un-
treated heartwood of baldcypress, redwood, or any of the
(When untreated woods are used, all pointss of
contact should be given two coats of hot creosote.)
a... is one of a series of reports issued b,, the Forest Products
Laibooat r' to aid the -ation's war effort. Results here reported are
p-ell-i:-.;--y and ;na; le revised as additional data become available.
--orest Prodr.cts Lpborator, Tcchnical 1ote io. 225, "Cause and Prevention
of 2li.:e S air. in Wood." 1940. Scneffer, T. C., and Lindgren, R. 1.
"Stains of Sanwood and Sanwood Products ane. T>.eir C.on-rol" U. S.
Dert. Ap-r. Tec.. Bull. 714, 123 '.p.
,.neo. "o. 1366
(5) Beams and stringers should preferably be of steel, or
pressure-creosoted timbers. Untreated durable woods with two coats
of hot creosote at points of contact may be used when neither of
the first two is available.
(6) If existing pile foundations are to be used, they should
cormp.ly with the requirements given as to height levels and drainage
conditions. All weeds, debris, and decayed wood and vegetation
must be cleared away. Any part of the pile foundation containing
decay should be removed or the decayed area cut out. All wood parts
should be painted with two coats of hot creosote.
(c) Air flues:
The lateral spacing between the edges of boards or of groups
of boards totaling 12 to 14 inches in width should be about 4
inches, so arranged as to form straight vertical flues in the pile.
Where losses from stain are high, the flue width should be increased
to about 6 inches. Where surface checking is the principal defect,
the flue width should be reduced to 1 or 2 inches.
(1) All stickers must be sound, thoroughly dry, free from
stain, and of uniform thickness.
(2) Each tier of stickers must be aligned and rest on a
(3) Stickers for 4/4-inch lumber shall be of nominal inch
stoc! or thicker and not more than 4 inches wide. For thicker lum-
ber of random length, stickers should be at least 1-1/2 inches thick,
for greater stiffness and strength, and should not be more than 4
(4) Stickers should overlap the ends of the boards at least 1/2
inch to reduce end checking.
(5) Stickers should not be more than 2 feet apart for hard-
woods up to 6/4 inches in thickness. For thicker hardwoods and all
softwoods, the spacing should be equivalent to five rows of stickers
for 16-foot stock,
(6) Aircraft stock should never be self-stickered.
(e) Placing of lumber:
(1) Piles should be erected of boards of equal length wherever
(2) ?ox piling should be used for mixed lengths. In this sys-
tem, the longest stick is piled in the outer rows and short lengths
within the nile, with one end of a board at one end of the pile. and
rno end of the adjacent board at the opposite end of the pile. In each
succeeding layer, the outside ends of boards should be kept immediately
over the unds of those below.
(3) Each layer should be composed of boards of the same thick-
(4) The pile should have a forward pitch of 1 inch for each foot
of height and a slope from front to rear of 1 inch for each foot of
(5) Tarrow piles are desired for stock that will withstand rapid
drying. Wide piles are desired for stock that may check and honeycomb.
Common pile widths range from 6 to 16 feet.
(6) Lateral space between piles should be about 4 feet. The
distance between the rear of one pile and the front of the next should
be about 8 feet.
(f) End coatings:
Wood dries more rapidly from the end grain than from the side
grain and is apt to check and split during seasoning unless end drying
is retarded by means of end coatings. Either cold or hot coatings can
One of the best cold coatings developed at the Forest Products
Laboratory iz an inexpensive hardened gloss oil thickened with barytes
and magnesium silicate.
The manufacture of hardened gloss oil involves technical opera-
tions of such exactness that it should be made only by a commercial
raint manufacturer. A hardened gloss oil suitable for end coating and
made in accordance with the following formula should be specified:
6 to 8 parts, by weight, hydrated lime.
100 parts, by weight, rosin.
57.5 parts, by weight, mineral spirits.
lo 100 parts by weight of this gloss oil, add 25 parts barytes
and 25 parts magnesium silicate. If a black coating is desired, one
or two parts of lampblack may be added. Because gloss oil so
thickened tends to become pasty after standing, the user should mix
small quantities as needed.
Paraffin is a satisfactory end coating for stock during air
seasoning, but it melts at kiln temperatures.
The following hot coatings are particularly satisfactory for
wood that is to be kiln dried after air seasoning:
(1) Coal-tar pitches or asphalts with melting points between
195 and 213 F.
(2) Mixtures of such coal-tar pitches and asphalts. (Exairaplo:
100 parts by weight of 213 and 40 parts of 155 F. coal-tar pitch
plus 25 parts of 220 asphalt.)
(3) Rosin and lampblack (100 parts by weight of rosin to 7
parts of lampblack).
(4) Any mixture of high-melting-point pitches and rosin.
When end coatings chip or shear off, a fresh coating should
All material should be under cover either in an open shed or
with roofs over individual piles. One satisfactory type of pile roof con-
sists of two layers of low-grade boards. Those in the upper layer should
be staggered with respect to those in the lower layer.
(1) A minimum front height of 6 inches above the lumber,
with a slope at least 1 inch to the foot, should be required.
(2) The ends and the sides should project sufficiently to
prevent snow and rain from beating into the lumber piles.
(3) The roof should be securely fastened to the pile.
The yard should be well drained and kept free of weeds and
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