■ 5 ENGELMANN SPRUCE AJ'P ITS PRESERVATIVE TREATMENT FOR TIES AND MINE TIMBERS By L. W. WOOD, Engineer and J. 0. BJ£W, Technologist Forest Products Laboratory,- Forest Service (J. S. Department of Agriculture The availability of Engelmann 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 cros sties in Colorado and Wyoming. Such use is the best testimony to the suitability of Engelmann spruce for these purposes. Ties Strength properties important in railway ties are bending strength, compres- sive strength, and hardness. The following tabulation is a composite rating bised on these strength properties in Engelmann spruce from Colorado, Montana, and Idaho, and some other western mountain species. Red oak, the most important wood used for cros sties, is shown as a basis for comparison. Species Rating Cottonwood, black 45 Fir, commercial white 58 Hemlock, western 64 Oak, red 100 Fine , lodueoole 56 Pine, ponderosa 54 Pedcedar, wes tern, 52 Spruce , Engelmann 47 Spruce , white and Sitka 57 -Maintained at Madison, Wis,, in cooperation with the University of Wisconsin. Rept. No. R1944-3 -1- Agriculture -Madison 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 Engelmann spruce ties give good service. Mine Timbers Bending and compressive strength and resistance to decay are also 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 other species. 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 small end. 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 column or post. Requirements for decay resistance in mine timbers vary 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. Preservative Treatment 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, Engelmann spruce crosaties, oarefully pressure -treated with creosote or creosote solutions, have an estimated average service life of from 25 to 29 years. Hept. No, R1944-3 -2- V 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 cross ties. Antichecking irons help to reduce objectionable checking during air seasoning. Experiments have also shown that penetration in both the sapvood and heartwood is consider- ably improved when the timbers an incised. Since Engelmann spruce is susceptible to checking and collapse if the treat- ing pressure is not kept 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 -3- June 1953 1 Table 1.— Service rec o rds on treated Engelmann spruce cross ties Location and date of installation i Railroad : Missoula, Mont, , 1910 Kingman, Ariz. , 1922 Kingman, Ariz, , 1922 Pinta, Ariz, , 1928 Pinta, Ariz, , 1928 Madison, VJis, , 1929 Madison, Wis,, 1929 Madison, Wis, , 1929 Laramie, Wyo,, 1927 Preservative and treatment No. Pac, Santa Fe Santa Fe Santa Fe Creosote-coal-tar solution (80-20), 6-3/4 lb./cu.ft. Zinc chloride 0.5 lb./ cu.ft. Petroleum 5 lb./cu.ft, Zinc chloride 0,5 lb,/ cu.ft. Creosote-petroleum solution (30-70) Creosote Santa Fe : Creosote-petroleum : solution (45-55) : 8 lb./cu.ft. C. M. St. P.& Pac. C. M. St. P.& Pac, C. M. St. P.& Pac. U. Pac. Zinc chloride 1.07 lb./ cu.ft. Zinc chloride 0,61 lb,/ cu.ft. Creosote 8.36 lb./ cu.ft. Creosote 6,67 lb,/ cu.ft. Zinc chloride 0,41 lb,/ cu.ft. Number in test : Condition of estimated average life 18 401 200 Years ^^ 25.4 « _-— CO a o o — ^^^ 21.8 \^m 18.1 u. (M r. = o> ~eo ► H ■ fM ■ — 2 "' ' = co - ~ ^^— 878 1,023 906 1,202 75 83 48 100 (hewn): 3 percent re* r moved in 8 : years ( sawn) t 14 percent re- moved in 8 years (hewn) (sawn) 0,2 percent re- moved in 8 years 4 percent re- moved in 8 years 22 29 26 16.3 Rept. No, R1944-3