THE MOISTURE CONTENT OP SOFTWOOD LUMBER SHIPPE D
S
FROM WESTERN MILLS IN THE SUMWR
By
Edward C . Pec k
Associate " .Mood Technologis t
. Forest Products Laboratory, Madison, 7 :is .
During the months of July end August of the pas t
summer (1928) the U . S . Forest Products Laboratory conducte d
a survey to obtain information on the moisture content o f
softwood lumber at the time of shipment from western mills .
The mills visited arc located in Montana, Idaho, Oregon ,
Washington, and California . This survey was for the purpose o f
obtaining more adequate inferriation than that whi h had bee n
p rocured in the previous moisture-content surveys', which wer e
limited to winter conditions for this western region .
c
The specimens for the moisture-content determinations were collected at 28 mills and included 9 species :
Western yellow pine, western white pine, sugar pine, Dougla s
fir, western hemlock, redwood, white fir, western larch, an d
Sitka spruce . Four hundred and thirty-sie lots of lumbe r
were tested ; each one ooneisted of oiprcximately 40 moisture- content determinations on individual boards of the sam e
seecies, size, and grade, seasoned and stored in the sam e
:manner . All of the lots were selected from stock that wa s
actually being shipped or was in shipping condition . Th e
individual moisture-content determinations amounted t o
17,000 .
The variety in the lumber tested and trio record s
kept arc illustrated by the representative s :liume 't de cribc d
in Table 1 .
1 T
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i+ . 2 . Peck . "The Moisture Content of Snftwood Lumber a t
the time of Shi p ment from the Mill . "
A :erican Lumberman No . 2763, 36-38 (Apr . 21, 1B) ;
Southern Lumberman 131, No . 1699, 40, 42--43, 47 (Apr .
21, 1928) ; Timberman 29, No . 7, 38-40, 44 (May, 1928) ;
Stich-Ecor-Finish 10, No . 1, 30-34 (May, lO?8) .
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'The object of the investigation was not to com par e
• ' • • the moisture-content values of lumber dipped from individua l
' " . mills or from the different regions, but to obtain informa tion regarding the moisture content of the different grade s
.Tr; ,' "Of lumber as shipped during the summer from the wester n
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lumber-producing regions as a whole .
The results are presented in two ways, in a serie s
of bar charts and in two charts showing the relation o f
{
average .moisture content and uniformity of dryness . On the
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bar charts (figs . 1 to 8, inclusive) the height of each ba r
'indicates in percentage the number of r:? eces thst had a is ture--content values falling within the group that it r .C " ;`.
cents . Figure 1, for instance, shows that 40 per dent _ o f
the pieces it records had a moisture ccnten t of 8 per cen t
-i • cr more and below 12 per cent . The noin.ts Nottec~ ' on th e
ti i• •
two summary charts (figs . 9 and 10) show for the individua l
lots both the average moisture content and the moisture con- tent below which 90 ner cent of the pieces in the lot fell .
.The average is plotted vertically and the "90 per cent "
print horizontally . The upper 10 per cent of the pieces i n
each lot, that is, those having the highest moisture-conten t
values, were discarded in order to be certain of eliminati n ,
all cxtrenely irregular values . The renge in moisture conten t
j n the repra.ining 90 per cent of the pieces gives a fair -sal s
for comparison among different lots of lumber and among
various kinds and grades .
Figure1, ,--Kiln-dried Selects .
This chart includes moisture-content tests on nine species : Sugar One ,
;western yellow Dine, western white pine, Douglas fir, western
LeuPlock, redwood ., white fir, western larch, and Sitka spr=ice .
'ri.te average moisture content cf the samples in this gred e
is 8 .8 per cent, with large representations in the 4
8
-rd. the 8 to 12 per cent groups .
' igure 2 .---Kiln-dried Floorir.t _ Two s p ecies ar e
iloluded here : Douglas fir and western b :Wn"w .•c'-.: . The rt,erage moisture content of all the flooring sesled is 8 .7 no r
cent, The concentrations of moisture-content values are i n
the 4 to 8 and the 8 to 12 per cent groups . The drying o f
flooring was more uniform than that of any ether kind o f
. lumber, fewer wet boards being present .
Figure3 .--Kiln-dried Shop . The species repre sented here are sugar pine, western yellow pine, Dougla s
fix, and Sitka spruce . The average moisture content i s
-7 .7 per cent, with a very heavy concentration in the 4 t o
8 per cent group and with almost all of the boards drie d
below'20 per cent moisture content . The sho p lumber wa s
kiln dried to a lower average moisture content than an y
other kind .
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Figure4..--Kiln-dried Common . The srec'ies represented in this chart are sugar pine, western yellow nine ,
white fir, Douglas fir, western hemlock, western white mine ,
western larch, and Sitka spruce . The average moisture con tent of this grade of lumber is 12 .1 per cent . The distribution of the moisture-content values of the individua l
samples shows a concentration in the 8 to 12 per cent groum ,
with a large number of high values of moisture content . Th e
large number of wet boards is due to the practice, in ma'VT
instances, of drying common lumber only to a relativel y
high moisture content .
Figure 5 .---Kiln.-dried Dimension . Three specie s
are included in this chart ; Douglas fir, white fir, an d
western larch . The average moisture content for the lumbe r
represented is 14 .8 per cent . The irregularity of th e
g roups in the figure is due to the relatively small numbe r
of lots obtained .
The very great concentration'in the 8 t o
12 per cent group is caused by several lots dried to meisture-content values unusually low for dimension stock .
Figureo .----Air-dried Selects . Nine species ar e
represented on this chart : Sugar pine, western yellow pine ,
;r estern white pine, Douglas fir, western hemlock, white fi r
estern larch, redwood, and Sitka spruce . The average :mc e
ure content is 13 .7 per cent with large numbers of individual samples falling in the 12 to 18 and the 8 to 12 pe r
cont groups . There is also a heavy representation in th 1 5
to 20 per cent group . The inclusion in this grade of a ccesiderable amount of lumber from a slow-drying species ceeee J
the average moisture content . to be higher than that of th e
common grade .
Figure 7 .---Air-dried Common . Tn this grade : 1
lumber there are seven species : Sugar pine, western :e l o -, r
pine, western white pine, white fir, Douglas fir, westc o
hemlock, and western larch . The average moisture coat m t
is 12 .{3 per cent . The individual moisture-content valu e
are heavily concentrated in the 8 to 12 per cent group wit h
another concentration in the 12 to 15 per cent group .
.
Figure 5 .----Air--dried Dimension . Four species ar e
represented in this chart : White fir, Douglas fir, wester n
hemlock, and western larch, The average moisture content o f
the samples is 15 .4 per cent . The moisture-content value s
of the individual pieces are concentrated in the 12 to 1 8
and 18 to 20 per cent groups .
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Figure9 .--Kiln-dried Lumber . All the species of
wood and Ell the kinds and grades of kiln-dried lumber ar e
included in this chart . Each point represents one lo t
(approximately 40 individual moisture-content determinations) ;
the p osition of the point indicates the average moisture con tent and the moisture content below which 90 per cent of th e
pieces in the lot fell .
The points for the lots of summe r
kiln-dried lumber group themselves about the diagonal lin e
(from lower left to upper right) that was located from th e
points plotted for the moisture-content studies made o n
lumber dried in the winter . This grouping means that th e
relationship of average moisture content and range of moieture content (within the lots} remains nearly constan t
throughout the year . In other words, whether the lumber i e
dried in the winter or in the summer, with a given averag e
moisture content, 90 per cent of the boards may be ex p ecte d
to have moisture-content values below a certain point .
Figurel0 . -Air-dried Lumber . This chart i a .imilar to Figure 9 except thst it represents the air-drie d
lumber, all species, kinds, and grades . There is also a
reasonably definite relationship between the average an d
the 41 90 per cent" point in the air-dried lumber, which i s
approximately the same for winter and for summer air seasoning .
As mentioned elsewhere, the diagonal lines appearing in Figures 9 and 10 are taken from the similar figure s
for the report on the cor r esponding survey of moisture-content conditions in winter' ; the lines show the moisture content relationship usual during the winter in the territor y
investigated .
The close proximity of the summer points t o
these lines means that the same general relationship of average moisture content to maximum moisture content (within th e
90 per cent limit} holds all through the yer . On the othe r
hand, comparison of the results previously reported with th e
present results makes evident the low averages and the mal l
ranges of moisture content in the summer-shipped lumber .
It
is impossible to say whether this is due solely to the climatic factors or to improvement in seasoning practice sinc e
the original survey . Nevertheless, for the western region s
examined, the moisture-content values of the present sumacrseasoned lumber, both air-dried and kiln-dried, beyond question arc eonsideiably lower than the values of the winter seasoned lumber .
2 Alt neugh the results obtained for the summer survey of th e
sonthern pine region are included in the ch ests of th e
previou report, the effect on the winter values, a s
` shown by the unpublished detail data, is sufficientl y
m^.1l to be neglected here .
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