ENGELMANN SPRUCE AVD ITS FTKRSERVATIVE TREATMENT
S/ FOR TIES AND MINE TBIBERS
L. W. WOOD), Engineer
J. O. BIJEW, Technologist
klForest Products Laboratory,-1 Forest Service
S\ ---' U. .S. Department of Agriculture
The availability of Engelmannn spruce makes it a useful species for railway
ties and mine timbers in the western Mountain States, This is in spite of
the fact that its strength properties and natural durability are not so
favorable as those of many species. A 1944 survey indicated a production
for that year of about 20 million lineal feet of mine timbers and a million
crossties in Colorado and Wyoming. Such use is the best testimony to the
suitability of Encelmann spruce for these purposes.
Strength properties important in railway ties are bending strength,compres-
sive strength, and hardness. The following tabulation is a composite rating
based on these strength properties in Engelmann spruce from Colorado, Nontana,
and Idaho, and some other western mountain species. Red oak, the most
important wood used for crossties, is shown as a basis for comparison.
Cottonwood, black................... 45
Fir, comprcial white............... 50
Hemlock, western................... 64
Oak, red........................... 1 i00
Pine, lod.epole................... 56
Pine, ponderosa.s.. *.. ............. 54
Redcedar, western....,.........., 52
Spruce, Engelmann.....*............ 47
Spruce, white and Sitka..........,.. 57
maintained d at Madison, Wis., in cooperation with the University of Wisconsin.
Rept. No, P1944-3
Though not a species of high natural durability, Engelmann spruce, when care-
fully treated with an effective preservative, has a service life of approxi-
mately 25 years or more in railway ties (table 1). A survey of western
mountain railroads indicated occasional but not excessive breakage of
Engelmann spruce ties. Ties should be placed on good ballast and should
be protected by tie plates under the rails. With these precautions treated
Enfelmann spruce ties give good service.
Bending and compressive strength and resistance to decay are alsd important
in mine timbers. Strength, however, is related fully as much to grade and
presence of defects as to the species. Tests of Rocky Mountain mine timbers
showed that the grade factor often over-shadowed the effect of species, so
that little difference in strength was observed between Engelmann spruce and
Mine timbers may be round or sawed. Strength tests show that a round timber
has the same bending and compressive strength as a square timber of the same
cross-sectional area. Where there is appreciable taper, the diameter of a
round timber should be taken at a point one-third of the length from the
Deep season checks may be present in beetle-killed logs. These may sub-
stantially reduce the bending strength of a short, deep beam, but they have
little effect on the strength of a coliuin or post.
Requirements for decay resistance in mine timbers very widely with the
presence of moisture, ventilation, and permanence of the installation. Un-
treated Engelmann spruce may be used where long life is not required. Treated
Engelmann spruce can be used for more permanent installations. Decay problems
in mine timbers are reduced by early removal of the bark and by open piling
of timbers to afford as much air seasoning as possible before they are placed
in the mine.
Engelmann spruce is a wood of rather low decay resistance and therefore will
not give long service as crossties and mine timbers unless treated with wood
preservatives. Service records on treated crossties of Engelmann spruce are
presented in table 1. These records are limited but show that, in the
region in which they have been installed, Enfelmann spruce crosaties, carefully
pressure-treated with creosote or creosote solutions, have an estimated
average service life of from 25 to 29 years.
Rept. No. R1944-3
This species is resistant to treatment, especially in the heartwood, and
therefore requires properly controlled treating conditions to obtain satis-
factory results. Treating temperatures of 190 to 200* F. have been found
essential for effective results when impregnating with creosote or creosote
solutions. Air seasoning seems preferable to heating in oil or steaming as
a means of conditioning prior to treatment, on the basis of the experience
thus far in treating Engelmann spruce crossties. Antichecking irons help
to reduce objectionable checking during air seasoning. Experiments have
also shown that penetration in both the sapwood and heartwood is consider-
ably improved when the timbers aro incised.
Since Engelmann spruce is susceptible to checking and collapse if the treat-
ing pressure is not kIcept within a moderate range, the maximum pressure per
square inch should generally be under 140 to 150 pounds, and when the full-
cell treatment is used, it should not exceed 130 pounds.
Rept. No. R1944-3
Table 1.--Service records on treated Engelmann spruce orosetiesa
Location :Railroad I Preservative I Number Condition of
and date of : s and in : estimated
installation r a treatment test s average life
--------------------------- ----- ... ..--.......-- .--- ..--- .---....
S : Years
Missoula, Nont.,:No, Pac, -Creosote-coal-tar 18 | 25.4
: Santa Fe
t solution (80-20),
: 6-3/4 ib./cu.ft.
tZinc chloride 0.5 lb./
:Petroleum 5 lb./cu.ft.
:Zinc chloride 0.5 lb./
t solution (45-55)
1 8 lb./cu.ft.
:C. M. St.:Zinc chloride 1.07 ib./:
: P.& Pac.: cu.ft. I
:C. M. St.:Zinc chloride 0.61 lb./:
P.& Pac.: cu.ft. I
: iCreosote 8.36 lb./ ,
:0C. M. St.:Creosote 6.67 lb./
P.& Pac.: cu.ft.
:U, Pac. :Zinc chloride 0.41 lb./:
: 0 cu.ft. :
S878 (hewn):3 percent re-
t moved in 8
a : years
i1,023 (sawn)a14 percent re-
t moved in 8
a r years
(hewn)-0.2 percent re-
l moved in 8
(sawn):4 percent ir-
t moved in 8
Reot. No, R1944-3