Air seasoning of lumber at small mills


Material Information

Air seasoning of lumber at small mills
Physical Description:
Mathewson, J. S
Forest Products Laboratory (U.S.)
USDA, Forest Service, Forest Products Laboratory ( Madison, Wis )
Publication Date:

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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 29318664
oclc - 229911267
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The operator of a small mill can sell his product more easily by giving proper
attention to details of drying that he now ignores. If he will go far enough
in improvin,- his practice, he will succeed in selling his lumber when buyers
are purchasing lightly, anti even a little attention to the neglected details
will bring easier sales. Minimizing seasoning degrade, without excessive in-
crease in dryiing, tire.c or in handling charges, is necessary for quality drying
and the sales advantage that quality brings.

Yard lumber can be stacked so as to insure more circulation or less as needed
by the species in the pile to minimize degrade. All lumber either gives off
moisture to surrounding air or takes it up until the moisture in the lumber
comes to a balr.nce with that in the air. The rate at 'ilicrh an exposed surface
in a yard piece gives off moisture depends upon such climritic factors as dry-
ness, teomperature, and wind, which change with both the locality and the sea-
son. Although these factors cannot in themselves be modified for dr:,ing pur-
poses, proper piling will aid materially in producing the results desired.

* The movement of air in a yard pile is of two types. Horizontal circulation,
which is cius3d primarily by local wind currents, can be regulated to some
degree by variation in yard layout, foundation construction, piling methods,
and arrangement and spacing of piles. Vertical circulation, which is like-
wise impol tant, is downward *-:)-en the interior of the pile is cooler than the
surrounding air, but upward when it is warmer. T'-e vertical mov.crrnt can be
regulated to some extent by the spacing of the vertical air ras.-.a.'es within
the pile and by altering the pile foundations.

The seasoning defects that cause degrade may be divided into three groups:
(1) sip stain and decay, (2) check, honeycomb, and loosened 1.nots, and
(3) warp, which includes bow, cup, crook, and twist. The three l"" of
seasoning; degrade that come from these r-oups may be minimiz-"! b (1) s-eed-
ing up the drying process, (2) retard'ing it _11 it stock
firmly in proper nliniri-erit, whatever the ate --iof-fnlri -',n.. the
species especially susceptible to blue-stEle te spwo d are
southern yellow pine, eastern and western white pine, pon.lrro a a d sugar
pine, basswood, sue.c.tgum, and maple. Ano1 F the .s[eoi,-:';iall s.:scp-
tible to check are oak, hickory, sycamore, beecharid hard maple.

The degree to w1T.lch it is practical to imn r ve air-drvn, i varies
fr,'.m mill to mill. In general, the lar-ei'l-r ...n. !1cr trd
separating stock by -pecies, grade, thickne a,- 4. ., j nith, 4dy Ferra-
nent mills can do more in drainage, grading, and foundation Jinprovrn.ent.

Rept. No. R.'-'?.-,

*See outline in Small Sawmill Improvement Working Plan, March 1930, for explanation of indexing system proposed
f Maintained at Madison 5, Wisconsin in cooperation with the University of Wisconsin
Agriculture Madison

More extensive discussion of air drying, including the use of special equip-
ment for handling packages of lumber, is given in FPL Report No. R1657,
available from the Forest Products Laboratory, Madison 5, Wis.

Flat Piling

Ordinarily, lumber is piled flatwise for drying, With this method the drying
rate is relatively slow and the weight of the pile tends to keep the stock
from warping. It is therefore suited to species in which check, honeycomb,
and warp are likely to occur and less suited to species in which sap-stain
degrade is probable.

The follcoiin; suggestions apply to flat piling.

Choose a well-drained site; for species that withstand rapid drying, it
should be fully exposed to the wind. Free it from brush and weeds. The
foundations must be firm and must raise the pile above the ground to assist
air circulation under it. Piers and beai.ris are highly preferable to other
types of support, such as stringers laid on the surface of the ground. At
peirivrin'rit yards a practical construction consists of piers of concrete or
creosoted timber supporting substantial stringers across which beams for
sticker support are spiked. At portable operations, foundations of standard
stock to be marketed when the pile is torn down can be made as follows:
Crosscut a reasonably sound 15-inch log of low value into bolts to provide
piers that elevate the first course of lumber at least 18 inches from the
ground and give it a slope of 1 inch to the foot from front to rear. Scrape
to firm soil at 12 points and bed the piers carefully (fig. 1).

Give the front of the pile a pitch toward the alley of 1 inch to the foot
of height and aline each tier of stickers parallel to this front. Make the
front of the pile smooth, avoiding especially projecting ends that would
lead rain or drip into the pile.

Some separation of stock by thickness and species is usually practicable
and, in softwoods, by length. An elementary length grouping consists in
putting 6-, 10-, and 12-foot lengths in one pile and 8-, 14-, and 16-foot
lengths in another. For this lay a cross beam on each row of three piers,
usint, a 6- by 8-inch beam or its equivalent (fig. 1). In laying courses,
intersperse the 1cngr stock uniformly across the pile, always placing a
long piece on the outside and keeping each tier of uniform length. Adjacent
short-ienpth tiers of boards should be flush with the front and rear faces
of the pile (box piling). Softwood boards 3, 4, and 5 inches wide can be
put in the samne pile. The 6-, 8-, 10-, and 12-inch widths are piled sepa-
rately. Space boards in the course 3 inches apart and place boards in
successive courses directly over those below. In the case of 2 by 4's
likely to crook, pile the 2- by 4-inch stock with the 4-inch face vertical
ari." space adjacent pieces in the course 1 inch apart laterally. Sticker
with 2- by 4-inch stock, with the 4-inch face horizontal, placing one
sticker over each beam, making four to the course for the 16-foot stock
or three for the 12-foot stock.

Hardwoods are usually piled separately by species and thickness, but all
widths and lenr-ths are put in the same pile (box piling). For this, lay 4

Rept. No. R''-3-


a 6- by 8-inch stringi-cr nlon each longitudinal row of piers, on ed e, Lu'id
alirec to su; T ort the lumber evenly. Then ..,ly cross beams at each end and
at 2-foot intervals 'etwe.a' (fig. 2). The airi in box piling is to build up
tie'-s, separatc'I i flues, in such a rF.,-iLer that the ,'. rious l.-. ,t.-s are
supported firmly ani.d the Ilues are unobstructed from top to bottom. A
given tier is -,ale up, as far as possible, of boards of similar length;
the lon nst bn'rdxt 'o into "re outside tiers with additional tie: ; of I-rp
boards uniformly distributed across the pile. Tier width approximates 12
inches, so that each layer in a tier 'n.v be formed of two 6-inch boards, or
an P- a..1 a 4-inch, or a single 10- or 12-inch board. Flues between tiers
aveca'-'e about 3 inches in width; '.e.t; e losses from stain are paramount,
increase this width up to 6 inches, and where shrinli'c defect,- do inite,
rednee it. Cra','. in, tiers straight up assures the unobstructed vertical
flt,;:" that 're conducive to uniform Ii-inC.

7',:. choice of stickers for boards less ti.-ir 8/4 inches thick is among dry
narrow stock, edginig, and strips sawed for the pur'- se. Sef-stickerinp
is convenient, but whe-'ei it would lead to c rious losses, through stain
and check, tl.} use of narrower and drier stickers is advantaeous, At
per":.r. rnt yards, stickers nlit. 1 by 2 inches for softwood and 1 by 1-1/2
inches for hardwood -re sa'e 1 preferablly from dry heartwood, At Yortablle
mills, edgr:n. -:: that have air dried for about a month ;:r-rvide relatively
cheap, partially dir stickers.

Roof all piles by placing' cross srprorts (t'.:o 2- by 4-inch by 8 feet
laid flatwise, one on top of the other) at front, center, and rear to
raise the roof off the lumber and then by putting a dor ble layer of
low-value stock on tlese supports so as to project 2-1/2 feet b",'... 1
the rear of the pile; stare,-' all oerni'D:~s in the two layers of roof
boards. At the front allow a 1-foot overhar., a..., if ..ecnssary, hav%
the front cover partly overlap the rear cover. In windy regions the
roofs should be wired down. The spac>.-- between piles should be 4 feet,
and, where edging stickers a-'e used, alterna' e piles should be set back
a foot to avoid the interlocking of random-length stickers, Rear 'll*-"s
should be at least 8 and rain il7ys 16 feet wide,

Since the drying rate and ti.e consequent d?:"rade from blue-stain, decay,
or shrinka-e defects are likely to vary with the location of the pile,
the sreciez of wood, and the season, some refir.e.,rts in piling practice
ma. be summarized as in table 1.

Rept. :o,. 7-'i" -.

Table l.--Methods of piling yard lumber to minimize seasoning degrade

To reduce the occurrence of --


: Warping :

Blue stain and decay

---------------------------: ----: ------------------------------------ -------------

Lower the foundations.:Use

Decrease the spacing :
between boards and :
between piles.
Use thinner,narrower
Place the end stickers:
so that they project :
beyoiInd the ends of
the pile.

Use end coatings.

of uni-
and sup-
and suf-

: Raise the foundations.
: Increase the spacing between
: boards and between piles.
: Provide one central flared
: chimney or a series of narrow
: Use thicker, narrower sticker,
Narrow the piles.
: Provide short chimneys )
: (1/3 or 1/2 height of ) The 1
: pile). ) part
SUse thicker stickers ) the p;
in the lower part of ) only.
the pile. )

Stain or
out the


End Pilingi

Lumber oiled on end is comparable to a flat pile tipped on end. End piling
is economical of labor, since one man can pile and unpile the lumber, and,
according to some operators, it gives relatively fast although not uniform
drying. Because of the speed of drying, however, thick stock, 8/4-inch and
upward, of most species would be susceptible to excessive checking and there-
fore it is flat piled. End piles can be built to take random widths and
lengths by piling like widths and, preferably, lengths, in the same row. In
its simplest form, end piling requires a floor, a central rack, and strips
supporting a single series of stickers. The floor is cull stock and, for
portable mills, can be improvised from edgings supported at 2-foot intervals
by slabs grounded so as to level the floor roughly across, although not
necessarily along, the pile. Lay the floor several weeks before stacking to
give it time to dry. The 2- by 12-inch by 12-foot cap plank of the rack is
saT-ported 8 feet above ground by 4- by 6-inch upright posts, which are given
stability by the 4- by 6-inch braces shown in figure 3. The sticker supports
are 1- by 4-inch strips continued from the central rack and nailed lightly
to the pile edges. When a single sticker to the course suffices, the height
of the sticker is 8 feet above the ground. When the warping hazard requires
more stickers, the spacing is about 4 feet apart. To start, put a sticker,

Although the terms "end piling" and "end racking" are similar, they are
widely used in the trade to refer to entirely different methods of piling,
which can give results that are quite unlike.




Rept. 'Io. 1i,"-.

either an edginfr or narrc i st)ck, across the sticker supports, and lay the
first *,ourse, tilting th,-. boards against the zupiort, The space between
id3ja-cnt boards approximates 8 i. hes. The exact width of the pile, ..ih ih
arroxi.mates 10 feet, dope ils uy-:.ri the frequency of occurrence of the
va-ious widths. Succeeding courses are a repetition of the first; care
shciild be exercised:1 to aline tier:, to make the 8-uinch rcinc co i':,i-ruus
the full ...-i th of the pile and to tilt boards parallel to the correspond-
ing ones in the preceding course. Load the rack evenly on each face up to
8 thousand board feet to a side before attempting to loal one face more
heavily than the other. Such piles are from 75 to 100 fe-;t in total length

End Ra-.1n

Two .;s of lumber crossing like an X, or 'roferably like an inverted V,
are r'o, ra.ked. i'..- resulting open pile gives a drying; rate too rIpl 1 for
mos-t woods if dryin- is continued to the air-dry condition. This method
is a '.i.-able whjrc rpc'cdy partial dr., i ,< is desired: for e:z IT Ie, to
carry stain-susceptible stock below the stain-favora.le c.,nr lition or to
lighten the load betueern the mill and the concentration yard. Ordinarily,
stock be brought to a condition of l-:, stain degrade hazard in 3 to 15
days, depending upon the i.ether, and may be then flat piled or sent to
thie con-entration yard. The essential features of such a rack (fig. 4)
are a rid 'e pole, ba.-e supports, and n-mir].:'e supports. Where valuable
st..:'?k is involved, the refinmrients desirable are to elevate the base
supports a foot above the ground ,lnd to ,m-t:e separate racks for each
]'.TV., in order to insure that the lumber shall cross at ibs extreme

Crib Piling

Crib piling is another method for .-- :':dy martial dryinE that is practiced
by small i1l3 cuttiJ: pine. It eliminates foundation, stickers, and
pile covers, but requires excessive yard space -nd is likely to cause high
d-"ra.b- fr-.'. stain at tLe ends whl.ere the prl-rnl:: are crossed and from warp
in the lon <, unsupported interval 'u,'yn ends. Separate piles are made
for each' length by cribbing three tiers in the form of a triangle, Xhe
first p2ank rests on supports at each c u'l, with one end of tle second
-lan:. crossing the first above a s>:".rt anid li- other ,. resting upon
the third support of the tria-i-1e. Tli. third plank closes the triangle.
In succeedi7 courses this crib work is carried to a heig t convenient
for one-ma:n stac'.in (fig 5). The planks cross directly above the

Contributed by
J. S. M on, S. iriop
Forest Froduct. Lab *-o -/
udison 5, ior. in
June 1(53


Digitized by the Internet Archive
in 2013

i .re 1. -- un
of soft

nation for piling

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Figure 2. --Foundation for flat
piling of hardwoods.

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- -* I. .

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Figure 3. --End piling.

Figure 4. --End racking.

Figure 5. --Crib pilin..


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