T— r? 1 14 4 ^> oi/ri TREATING WOOD IN PENTACHLCRCPHENCE SCEUTICNS By THE CCED-SCAKING METHOD Revised March 1948 librarV * MAR 12 1948 ATI** rU No. R1445 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wisconsin TREATING WOOD IN PENTACHLOROPHENOL SOLUTIONS BY THE COLD-SOAKING METHOD By J. OSCAR BLEW, Technologist Introduction Cold soaking is a limited-purpose treatment for the preservation of wood. In treating by the cold-soaking method, the wood is simply submerged in the preservative solution and allowed to soak for a few hours or days, Wood that is easy to treat, such as sapwood of pine or round pine posts con- taining a substantial sapwood volume, may absorb enough preservative and be sufficiently well penetrated during the treatment to provide a high degree of protection from decay and termites. In woods more difficult to treat, including the heartwood of most species, the results may be much less sat- isfactory. Treatment by cold soaking, because it permits greater absorptions and deeper penetrations of preservative, will provide more satisfactory re- sults than are obtainable by short dipping treatments. Cold soaking can sometimes be used to advantage when it is impracti- cal to use the more effective impregnation treatments. It has the advantage of being relatively simple and moderate in cost. It can be used with a variety of preservatives to meet different requirements as to color, clean- liness, paintability, freedom from odor, or other properties. Seldom, how- ever, will treatment by cold- soaking methods give as much protection from decay or insects as treatment by pressure or by hot-and-cold bath methods. Despite their greater first cost, these methods will often be cheaper in the long run because of the longer life they provide. Any preservative dissolved in water or in thin oils may be applied by cold soaking. The use of water solutions by cold soaking is often called the steeping process and is described in another publication.^ There are a number of preservatives, consisting of toxic chemicals dissolved in kero- sene, domestic fuel oil, or in similar oils, that can be applied by cold soaking. Pentachlorophenol is one such chemical, more commonly used than the others, with which the Forest Products Laboratory has experimented con- siderably. This report deals primarily with the use of pentachlorophenol -A partial list of publications describing various preservatives and non- pressure processes will be found at the end of this report. They are available from the Forest Products Laboratory on request. Rept. No. R1UU5 (Revised) solutions, but most of the information it contains vill apply as well to other preservatives of similar type. Coal-tar creosote, diluted with not more than an equal volume of low-viscosity fuel oil, and light oils contain- ing copper nuphthenate have been applied to fence posts by the cold-scaking method with treating results similar to those obtained with pentachlorophenol solutions. Pentachlorophenol Solutions of pentachlorophenol in light petroleum oil solvents have been widely used in recent years for the treatment of window sash and frames, also for treating other products where a clean, odorless, and nonswelling treatment is reouired, particularly when the wood' must be painted after treat- ment. The treating solutions are usually applied by short dipping applications since the products are generally not exposed to conditions favoring rapid decay or insect attack and thus do not require a more thorough treatment. The hi.^h toxicity, the resistance to leaching, and results of limited service tests indicate that pentachlorophenol solutions with a more thorough applica- tion may also be suitable for the treatment of lumber, fence posts, or other wood products to be used in contact with the ground. Pentachlorophenol is available in two forms -- dry flake, and concen- trated solution. When purchased dry it is in the form of dark gray flakes or crystals having a slight odor. When handled in this form, the chemical has a tendency to dust into the air. The dust is irritating to the mucous membranes of the eyes, nose and throat, thus the use of protective goggles and dust masks la recommended for workers mixing the solutions. Heating equipment is generally required in order to prepare solutions from the dry chemical. It is generally more convenient for the user without special mixing equipment to purchase a concentrated solution of pentachlorophenol and dilute it with the desired solvent. Concentrates are available requiring dilution with 2 to 12 or more parts of solvent (by volume) to prepare a 5 percent treating solution. Concentrates are either dark or light colored depending upon the use requirements of the material to be treated and the percentage of pentachlorophenol in the concentrate. Light-colored concentrates usually contain less preservative than those of a darker color. For treatments requiring a clean, paintable surface, light-colored con- centrates and solvents, such as naphtha, mineral spirits, or kerosene, should be used. Where such properties in the treated wood are not required, as in fence posts or rough lumber, the darker-colored concentrates and lower-priced petroleum oil solvents and even used crankcase oil, if reasonably clean, can be used. The use of dark-colored solutions makes it relatively easy to determine the depth of penetration in the wood after treatment. In making the selection, however, other requirements 6uch as drying rate, fire hazard and penetrating properties should be considered. There is some evidence to indicate that pentachlorophenol solutions prepared from the light oil solvents may provide less protection than those prepared from the heavier type of oils. Rept. No. R1UU5 -2- In mixing the treating solutions, it is important to have the proper proportions of toxic chemical and solvent. The weighing of all ingredients is recommended, but in the absence of accurate weighing equipment, an accu- rate liquid measure can be used providing the weight per gallon of both preservative concentrate and solvent and the percentage of chemical in the concentrate are known. If complete instructions for preparing the solution cannot be obtained, the proper quantities of concentrate and solvent can be arrived at by using either of the following formulas: 1. For obtaining the required number of pounds of solvent for each pound of concentrate . Pounds of solvent to be added to each pound of concentrate = a Where a = toxic concentration of concentrate expressed decimally. b = toxic concentration of desired treating solution expressed decimally. Example If the concentrate contains 2k percent pentachlorophenol and a 5 percent treating solution is desired, the weight of solvent required per pound of concentrate would be °"^ ," 0,Cl 5 - 3,8 pounds. 0.05 2. For obtaining the required number of gallons of solvent for each gallon of concen trats , Gallons of solvent required per gallon of concentrate = ( — - — ) (-=■) Where a = toxic concentration of concentrate expressed decimally. b = toxic concentration of desired solution expressed decimally. c = weight per gallon of concentrate. d = weight per gallon of solvent. Example A gallon of concentrate containing 16 percent pentachlorophenol weighing 8.I5 pounds is to be mived with fuel oil weighing 7 pounds per gsllon to obtain a 5 percent treating solution. The number of gallons of solvent required per gallon of concentrate would be °- 16 - °-°5 x 2^5 p ?> 56 gallons. 0.05 7-0 Eept. No. FJM5 -3. Treatment To obtain satisfactory results by cold-soaking treatment, the material must be well seasoned and free from outer and inner bark. A seasoning period of 2 to 6 months or longer, during the warmer, drier seasons of the year, is generally sufficient if the wood is open-piled at least a foot above the ground and is well ventilated. Material seasoned for a year or longer and even that seasoned for only several months under unfavorable conditions will probably absorb greater or even excessive quantities of preservative, but in wood that is thus handled seasoning is apt to be accompanied by decay. Such seasoning is therefore not encouraged. The material should be cut to final dimensions and all boring or framing should be done before treatment. If cutting or boring is required after treatment, the cut surfaces should be treated with a liberal quantity of the preservative applied by flooding or generous brushing. The equipment required for treatment by the cold- soaking method con- sists mainly of a leak-proof tank of sufficient size and strength to accom- modate the completely submerged material for the full time of the treatment. Some arrangement should be provided for keeping the material from floating above the level of the solution. Suitable weights, or cross bracing at- tached to the sides of the tank generally accomplish this purpose. In making the treatment, the wood is simply submerged in the preserva- tive solution and allowed to soak for a predetermined time, or until the desired quantity of preservative has been absorbed and good penetrations are obtained. For round fence posts of easily treated woods, a soaking period of 48 hours produces good penetrations. For various species treated by the Forest Products Laboratory, preservative absorptions during such periods have averaged approximately 90 percent in softwoods and 70 percent in hard- woods of those observed after continued soaking as long as one week. Soaking periods longer than one week do not appear to be justified except in special cases. Higher absorptions and some improvement in preservative penetration can be expected in cold soaking if the depth of immersion is increased. Limited soaking tests on southern yellow pine sapwood and Douglas-fir heart- wood lumber cf short lengths have shown absorption increases from 25 to 100 percent or more due to pressure increases at tank depths of 7 "to 10 feet. Where suitable tank equipment can be provided increasing the depth of immer- sion can be used as a means for obtaining greater absorptions in woods that are difficult to treat, or for reducing the soaking time for easily treated woods such as pine. The use of a vertical tank (fig. 1) can likewise be expected to provide improved treatment in the butts of fence posts providing the posts are placed in the tank and soaked with the butt ends down. This method of treatment, however, cannot be expected to materially improve pene- trations in woods, such as aspen (popple) or basswood, that normally absorb large quantities of preservative but show erratic penetrations. Rept. No. RlM*5 -k- The tank ehovn in the illustration was made by welding two hot-water storage tanks. Oil drums welded together would be more appropriate if a considerable number of posts are to be treated. The size, shape, and char- acter of treating tank should be determined by the amount and character of wood to be treated and by the character of acceptable containers available. Th§ following rough classification, based upon a limited number of species of round fence posts treated by the Forest Products Laboratory, should be helpful in the selection of woods that are best adapted to the cold-soaking treatment. The results indicate that the woods of group 1 are to be preferred. Group 1. Absorptions fair to good, and penetrations in sapwood reasonably good, after a soaking period of 1+8 hours . Round softwood posts Bound hardwood posts Pine, Eastern white Oak, black (high sapwood Pine, jack content) Pine, lodgspole Oak, red (high sapwood Pine, ponderosa content) Pine, red Oak, southern red Fine, southern yellow Group 2. Absorptions fair to good, and penetrations in sapwood fair, after a soaking period of *+8 hours or longer . Bound hardwood posts Cherry, black Elm, American Elm, slippery Hickory, shagbark Oak, white Group 3» Absorptions good, but transverse sapwood penetrations generally poor, after a soaking period of kS hours or longer . (Good end penetration is usually obtained, thus material not over 2 to 3 feet in length can be expected to show satisfactory treatment.) Round hardwood posts * Aspen Maple, soft Basswood Sweetbay Birch, white or Sweetgum paper Tupelo, swamp (blackgum) Maple, hard Willow Kept. No. RlM+5 -5- Group 4. Absorptions and penetrations pocr to fair after a soaking period of 48 hours or longer" ! Bound softwood posts Round hardvcod posts Douglas-fir (mountain Ash, green type)* Butternut Larch, European Catalpa Spruce, Norway Hackberry Redcedar, Western White-cedar, Northern Fir, white* ♦Penetrations in some cases fair to good but net uniformly so. Cost and Effectiveness of Treatment The cost of treatment by cold soaking can be expected to vary to a considerable extent according to the cost of the treating solution used, the size of the material, the number of pieces being treated, the quantity of solution absorbed, labor costs, and equipment costs. In the treatment of fence posts by the Forest Products Laboratory with domestic No. 2 fuel oil containing 5 percent pentachlorophenol, preservative cost 8 (1948 figures) alone varied from 6-l/2 cents to 62 cents per cubic foot of wood treated. The preservative cost will vary with the price per gallon of the preservative as well as with the amount absorbed per unit volume of wood. Costs for labor, equipment, and the surplus preservative that is required to keep the wood covered during treatment, but which remains after treatment, should be added to the cost of the preservative in arriving at the total cost of treatment. Round posts of some woods in Group 4 absorbed less than l/4 gallon per cubic foot of wood during a 48-hour soaking period while those of some woods in Groups 1 and 3 absorbed as much as 2 gallons per cubic foot in the same period. A post 7 feet long with an average diameter of 5 inches has a volume of approximately 1 cubic foot, A gallon of 1 to 10 con- centrate, costing $2.15, diluted with 10 gallons of domestic No. 2 fuel oil (12 cents per gallon) costing $1.20 would produce a treating solution at a cost of 30.5 cents per gallon. The effectiveness of the cold-soaking treatment of wood with penta- chlorophenol solutions has not yet been fully established since this treat- ment has not been applied for a long enough period. Conclusive service infor- mation is not available at the present time, except on posts known to be inadequately treated (see last paragraph). Experiments, however, on southern yellow pine fence posts treated by pressure impregnation with 6.4 and 6.7 pounds per cubic foot of 3 percent and 5 percent pentachlorophenol, respec- tively, in spent crankcase oil indicate that good results may be expected from material treated with these preservatives if sufficient absorption and good penetrations are obtained. The posts have been in test in Mississippi for approximately 11 years. In that time all of 99 posts treated with the Rept. No. R1445 -6- 5 percent solution and all but one of the 99 posts treated with the 3 per- cent solution were in good or servicea.ble condition. These results with the 5 percent solution are similar to those obtained with posts in the same test treated with 6 pounds of coal-tar creosote per cubic foot. All of the untreated posts installed at the same time have been destroyed because of decay and termite attack. The average life of the untreated posts was 3*3 years . Since retentions as high as 5 or 6 pounds per cubic foot and penetra- tions comparable to those obtained by pressure treatment are generally not obtainable through cold soaking, the effectiveness of this method of treat- ment may not be so high as that reported for the pressure-treated posts. The Forest Products Laboratory during 19^2 and 19^-3 installed near Madison, Wis., experimental posts of several species treated with pentachloro- phenol solutions by cold soaking. Later installations have included treat- ments by cold soaking with fuel oil containing copper naphthenate and with solutions containing 50 percent coal-tar creosote and 50 percent fuel oil. Most of these experimental posts were in good or serviceable condition when last inspected during the fall of 19^7- However, there have been a high per- centage of premature failures after b years of service in asjjen and white birch posts due to inadequate preservative penetrations in the ground line zone of these posts. These and similar early failures reported on tests in Minnesota on treated aspen posts indicate that all woods cannot be treated satisfactorily by the cold-soaking method. The user of the method should therefore select only those woods which experience has shown to take treat- ment satisfactorily. The cold-soaking treatment of posts of woods in Group 3 (see page 5) cannot generally be recommended. Rept. Ho. RH145 -7- List of Forest Products Laboratory Publications on Ncnpressure Treatments Bulletins Preservative treatment of farm timbers, U. S. Dept . Agr. Farmers' Bull. 7kk. Revised 1928. Mimeographs RI5U Methods of applying wood preservatives, (revised 19^) • R1693 Preservatives for wood poles (19^-6). K621 Preservative of timber by the steeping process, (revised 19^+5) • R76l Preservative treatment and staining of shingles, (revised 19^7). R919 Preserv •.• ive treatment of window sash and other millwork, (re -.sod 19^5). R1190 Testing wood preservatives, (1938). RIU9 Wood preservatives, (revised 19^0 . Rli+68 Selecting a suitable method for treating fence posts (19^+6). Miscellaneous mimeographs: Celcure (19^) The Osmose process (19^) Chromated zinc chloride (19^*0 List of coal-tar creosote producers and dealers in the United States (19^1) Zinc chloride producers and dealers in the United States (19^7) Seme companies that design or build treating plants (19^+Q) Partial list of suppliers of pentachlorophenol wood preservatives for the treatment of fence posts, poles, and structural lumber and timbers (19^5) Rept. No. HIM* 5 HINGED ARM FOR KEEPING P05T5 SUBMERGED ^l^Eg= % SET. RANGE BOILERS WELD OPEN TOP y OVERFLOW P/PE BUTT END5 DRA/N AND CLEAN-OUT LINE lj"- CHECK VALVE PUMP TO STORAGE TANK Figure l.--An arrangement for treating posts with pentachlorphenol solutions on a small scale. The main part of the system is the upright tank so that pressure caused bv the height of the liquid causes deeper penetration into the butts of the posts. Piping shown for a circulation svstem is helpful but it Is not essential. Z M 53258 F ,111111 II I 3 1262 08925 4345