yllpt" T-UlBt tArTIMOV Of rENct, POST TUATAtNT
Revised -febmary 1945
UNITED STATES DEPARTMENT OF AQUCULTURE
FOREST PRODUCTS LABORATORY Madison, WisconsiA
In ceepentieft wuh 60 univerghy of W040"ift
The treating method described in this mimeograph was developed and the original mimeograph prepared at a time when both zinc chloride and tire tubes were freely available and cheap. During the war, however, tire tubes are practically unobtainable and zinc chloride is available in limited Taantities and from few sources only. The tire-tube method, therefore, is not very practical for wartime use and will probably find little, if any use, until after rubber and zinc chloride become freely available again.
Forest Products Laboratory
TIRE-TUBE METHOD OF FZNGL POST TRJATIE:T
R. M. WIRXA, Engineer
3ence posts of nondurable wood can be made to have 20 to .30 years life, or even more, by thorough pressure treatment with coal-tar creosote or mixtures of creosote with other suitable oils. Similar results can be obtained with these preservatives by the hot-and-cold bath method of treatment described in Farmers' Bulletin 744, !'The Preservative Treatment of Farm Timbers." This can be obtained from the Superintendent of Documents, Government Printing Office, Washington, D. C., for 5 cents a copy (stamps not accepted). Hundreds of thousands of posts treated by these methods are now in successful service throughout the country. Many farmers and other post users have failed to take advantage of these treatments, however, and are continuing to use short-lived, untreated posts. While thorough impregnation with creosote is highly effective and economical, the cash outlay required fqr such treatment is considerable. No better treatment for posts is known but, if it is necessary to keep the cash outlay as low as possible, some' other method will often have to be used.
One of the simplest and cheapest methods that can be used with assurance of a moderate increase in durability is the tire-tube method, illustrated in figure 1, which is an adaptation of the old Boucherie process. It consists in treating thoroughly green, round posts with the bark on by forcing preservative solution endwise through the sapwood portion of the post. The method is not 'recommended for split or sawed posts, or pests that have started to season.' In making the treatment, the bark is peeled for a distance of 4 to 6 inches from the large end of the post, to provide a smooth, clean surface. A section of old inner tube about 2 or 2-1/2 feet long, cut from a used tire, is then slipped over the peeled surface and bound in place with cord, wire, rubber band, or any other convenient and suitable material. The post is then laid on a rack with the large end about 1-1/2 feet or more higher thai the small end. The loose end of the tire section is then fastened to a frame so that the preservative cannot spill out but will be kept in close contact with the end of the post, and a measured amount of preservative solution is poured in. In a short time the preservative will begin to flow into the sapwood of the post, forcing the natural sap out at the small end. 1When ll the preservative has flowed from the tire tube into the wood, the tube is removed and the post is taken from the rack.
The length of time required for the preservative to flow into the wood will vary with the quantity used, the kind and condition of the wood,
season of the year, thickness of sapwood, and other factors. Vith aspen posts 7 feet long, 8 to 24 hours were usually sufficient. Most rapid
Mimeo, No. R1158 -1(Revised February 1945)
treatment outdoors can be expected during warm weather. The preservative will flow into wood more slowly during cool weather and outdoor treatment by this method in freezing weather will usually not be practical, If posts are brought indoors for treatment in freezing weather they should be allowed to thaw out thoroughly before the treatment is begun.
Green Posts Required
The tire-.tube method is suitable only for wood that is thoroughly
green. The sooner posts are treated after cutting the better. If possible, they should be treated within 24 hours, especially in hot, dry weather. If ,the ends have dried too =mch they should be cut off for an inch or so until wet surfaces are exposed. If the posts must be held longer before treatment, the ends may be coated with paint-or similar material that will retard' drying, then when ready. to treat, an inch or more of wood can be sawed from each end. If it is convenient to keep the posts submerged in water (not floating) they will remain in good condition for treatment for many weeks. The Important requirement is that there shall have been no drying of the end surface that' the preservative must enter.
The ApparatusSections of inner tubes from used automobile or truck tires constitute the most important part of the treating apparatus. The sections should be about 24 to 30 inches-long and free from leaks. Small leaks zay be stopped with cold'tire patches or with small clamps like those used in chemical laboratories. A. small clamp that will serve for this purpose can be made with two small pieces of wood about 1/4 by 3/4 by 2-1/2 inches in size with'a 1/8-inch stove bolt through their center to draw them together (fig. 2, A, B).' It is always best to use'tubes that are somewhat smaller than the posts on which they are to be placed, in order to get a tight connection,' In attaching the tube it is merely doubled back over itself for about 4 to 6 inches and the folded edge stretched over the end of the post. The doubled-back portion is then easily unrolled into place. If the peeled surface is irregular it is well to spread axle grease or similar material over it before unrolling the doubled-back portion, to avoid leakage. After a few posts have been treated, experience will indicate the type of surfaces
that will require coatings of grease.
A very simple, home-made stretcher that will simplify slipping a.
small tube on a large post is shown in figure 2, C. It can be made of 4 to
6 smooth hardwood sticks about 3/4 by 1-1/2 by 24 Inches in size that are tapered at one end and hel d together by rubber strips out-from a tire tube. Two stretchers will be convenient if both large and small posts are to be treated;, one for small posts with 4 sticks and another for large posts with
6 sticks. By using the stretcher in the manner illustrated in figure 3, very small tubes can be made to stretch over fairly large post s with relative ease.
After the tube is on it should be tied in place by several wrappings of cord, wire, rubber bands, or other suitable material, to prevent leakage of preservative. A strip of inner tube about 1-1/2 inches wide and about
4 feet long will serve very well for the purpose. A single wrapping of No. 12 wire, tightly twisted with pliers, will also be useful for this purpose. Leakage at depressions on the surface of a post can be stopped by tapping the wire into the depressions. One experimenter reports that a tight connection can be obtained on posts with smooth bark, such as maple, by slipping the tube onto the post without removing any of the bark and binding it with a single wrapping of No. 12 wire.
Any convenient support or rack may be 'used that permits the small
end of the post to be 18 inches or more lower than the large end, provides a means for holding the loose end of the tire tube, and allows the drip to escape freely from the post. low racks will generally be found most convenient for lifting and moving the posts. The loose end of the tube may be tied to the supporting frame with rope or cord. Small 'to" clamps are very convenient for this purpose. If preferred., the posts may be allowed to stand upright against any convenient support.
If the drip from the posts is to be saved for mixing new solution,
provision muist be gade to, catch it in a suitable tank or barrel. A good weighing scale should be available,-also accurate measuring cans for measuring water and solution, Cans or pails marked off in- gallons and quarts will generally be useful.
If a large number of posts are to be treated the apparatus should be selected with considerable care, so as to make all operations as convenient
as possible. Much unnecessary labor can thus be avoided.
Only preservatives dissolved in water may be used, for oils will not penetrate satisfactorily when applied to green wood in this manner. Various
proprietary and nonproprietary preservatives in-water solution can undoubtedly be employed. At present, however, zinc chloride seems most promising 'because of its cheapness, availability, safety, and convenience, combined. with moderate effectiveness. Chromated zinc chloride is now more widely used by the wood-preserving industry than plain zinc chloride and may be easier to obtain. The chromated form may cost a little more but it is also claimed by its promoters to be more effective.
Zinc chloride is available in three forms:- granulated, fused, and
concentrated solution. In the granulated form it Is in dry, white grains or small pieces which dissolve readily in water. It must be shipped in airtight containers for, when exposed to the air, it quickly takes up moisture and the grains stick together or even melt in the absorbed water. When using this form, therefore, it is desirable to mix the entire contents of the container with water at one time whenever practicable. If any unused granules must be left in the container it should be tightly closed as quickly ,as -possible.
The fused form is very inconvenient to handle in small quantities. It is shipped as a solid mass inside of an airtightt container. It can be dissolved slowly by chopping holes in the container and placing both container and contents in the water or the container may be chopped to pieces andthus removed from around the zinc chloride mass. Since fused zinc chloride, when purchased in small quantities, is no cheaper than the granulated form, and may even be more expensive, there is seldom any advantage to the small, consumer in using it.
The most convenient form of zinc chloride for small users is the concentrated solution. Various manufacturers ship the solution in different strengths# usually about 48 to 72 percent. The purchaser should know what strength of solution is being furnished so that he may know how much water to add to make the proper treating solution, as well as what the zinc chloride part of the solution is costing him. The solution form is usually the cheapest to buy, except where there is a long freight haul. Since the solution is generally about half water the freight cost will be higher than on an equal amount of zinc chloride shipped in the dry form.
The cost of zinc chloride will vary'considerably wiih the quantity
purchased# the sizes of the containers, the.form (whether granulated, fused, or solution), and other factors. In solution form prices as low as 3 or 4 cents per pound (equivalent to about 6 to 8 cents per pound for the zinc chloride in the solution)-are sometimes quoted when several hundred pounds are purchased. To this cost freight must be added. In smaller quantities the prices are likely to be higher. Since the prices vary so widely the prospective purchaser should ask for prices from several companies on both the dry form and the solution form# stating the quantity desired. If the prices quoted include freight they will simplifZr comparing the net delivered cost, but usually they will be quoted f.o.b, the dealer's warehouse and the purchaser will have to determine the freight cost in order to make comparisons.
In asking for prices it should be stated that the zinc chloride is to be used for wood preservation a4d the dealer should be asked to state the purity of his product or the concentration of zinc chloride, if in solution The American Wood-Preservers' Association requires that in the solid form there shall be at least 94 percent of zinc chloride and not more than
0.1 percent iron. A moderate amount.of impurities is not objectionable. A 100 percent pure product would be very satisfactory, but usually too expensive.
Preparing the Treating Solution
While the work done thus far indicates that a 10 percent solution of zinc chloride will be suitable for treating posts of many species by the tire-tube method it is known that it will not be satisfactory for certain species that will be discussed later.
If the zinc chloride has been purchased in granulated or fused form, and is reasonably pure, a solution of approximately 10 percent strength can
Mimeo. No. R1158 -4-
be made by- mixing in the proportion of 10 pounds of the solid zinc chloride to 90 pounds of water. If the zinc chloride is 95 percent pure about 10-1/2 pounds will be required for 90 pounds of water. It is not practical to measure quantities of solid zinc chloride and, even with water, weighing is generally more accurate than measuring. However, when it is too inconvenient to weigh the water it may be measured. A gallon of water at a temperature of about 60" F. weighs about 8-1/3 pounds. For 10-1/2 pounds of 95 percent pure zinc chloride, therefore, about 10-3/4 gallons of water are required to make a 10 percent solution.
If the zinc chloride has been purchased in concentrated solution the amount of water required will depend upon the concentration. Table 1 shows the approximate proportions of concentrated solution and water required for the different strengths of zinc chloride solution commonly available, to produce a treating solution of 10 percent strength.
Strength of : Approximate amount of water to be added to 10 pounds
concentrated : of concentrated solution t'o make a 10 percent
solution treating solution
-------------- ---------------------------_ --------------------------Percent Pounds Gallons
48-1/2 38-1/2 4-1/2
50 A0 4-3/4
70 60 7-1/4
72 62 7-1/2
Amount of Solution per Post
It is considered good practice to have the posts absorb about 1 pound of zinc chloride per cubic foot of wood. For this reason different amounts of preservative solution are required for posts of different size. Table 2 will behelpful in determining the amount of 10 percent solution to use for
The average middle diameter of a post (for use with table 2) i s found by averaging the diameters of the two ends, the measurements being taken in-side the bark. When the ends of a post are not true circles, which is very often the case, it is desirable to measure the diameter at each end in more than one direction and thus obtain an approximate average figure. The average diameters obtained in this way for the two ends are then averaged together to give the average middle diameter. A high degree of accuracy is
The following example illustrates how table 2 can be used to determine the amount of 10 percent zinc chloride solution required to treat a post of a
Mimeo, 'ITo. R1158
Table 2.--Amounts of 10 percent zinc chloride solution required for posts of different sizes
Average :Approximate amounts of solution for posts that are:
middle ------------------------------------- -diameter: of post,:
inside : 6 feet long : 7 feet long : 8 feet long
bark : I.,
----: -------- -------- ----------Inches : Pounds :Gallons: Pounds :Gallons: Pounds :Gallons
A B : 0 : D : E : : G
3 : 3 : 1/4 : 3-1/2 : 1/2 : 4 : 1/2
3-1/2 : 4 : 1/2 : 4-3/4 : 1/2 : 5-1/4 : 1/2
4 : 5-1/4 : 1/2: 6 : 3/4 : 7 : 3/4
4-1/2 : 6-3/4 : 3/4 : 7-3/4 : 3/4 : 8-3/4. 1
5 : 8-1/4:1 : 9-1/2 :1 : 11 :1-1/4
5-1/2 : 10 : 1 : 11-1/2 :1-1/4 : 13-1/4 : 1-1/2
6 11-3/4 : 1-1/4 : 13-3/4 1-1/2 : 15-3/4 : 1-3/4
6-1/2 13-3/4 : 1-1/2 : 16-1/4 : 1-3/4 : 18-1/2 : 2
7 6 16 : 1-3/4 : 18-3/4 : 2 : 21-1/2 : 2-1/4
7-1/2 : 18-1/2 : 2 : 21-1/2 : 2-1/4 : 24-1/2 : 2-3/4
8 : :21 : 2-1/4 : 24-1/2.: 2-3/4 :28 : 3
8-1/2 : 23-3/4 : 2-1/2 : 27-1/2: 3 : 31-1/2 : 3-1/2
9 :26-1/2 :3 :31 :3-1/2 : 35-1/4:4
9-1/2 29-1/2 : 3-1/4 : 34-1/2 : 3-3/4 : 39-1/2 : 4-1/4
Mimeo. No. R1158 -6-
known size, Suppose a post is 7 feet long and hat an average middle'diameter of 4-1/2 inches. The amount of 10 percent solution required will be found in column D in pounds or column 2 in gallons, on the line with the 4-1/2 in column A. They show that about 7-3/4 pounds or about 3/4 gallon will be required to treat the post. Similarly it will be found that an 8-foot post with an average middle diameter of 7 inches will require 21-1/2
pounds or about 2-1/4 gallons.
Waste of Solution
Although most of the liquid that drips from the end of the post during treatment is the sap of the tree (mostly water), It will usually contain some zinc chloride. In all species treated at the Forest Products Laboratory, except the oaks aad hickories, the cluantities of zinc chloride in the drip were found to be small, generally less than one-tenth of a pound. The drip from the oaks and hickories, however, contained fairly large amounts of zinc chloride. The zinc chloride in the drip need not be wasted if the drip is saved and used in the preparation of additional solution. For practical purposes drip containing small amounts of zinc chloride may be regarded as water, that is, no consideration need be given to the small amount of preservative that it contains. The sugar and other materials contained ia the sap are in such small quantity that they need cause no concern, even if the solution becomes discolored. Nhen the zinc chloride in the drip is quite large, account should be taken of it in making up additional solution. Further discussion of this point will be found under
the heading "Species of !food."
Cans under the posts or a trough sloping downward to a large container are convenient for collecting the drip.
Summary of Treating Operation
The following summary of the foregoing discussion indicates the different treating operations and the order in which they should follow each other:
1. Peel bark from large end of post for about 4 to 6 inches, leaving a smooth$ clean surface so that a tight joint can be made between wood and rubber. (If the end surfaces of the posts are dry, cut the ends back until
wet wood is exposed.)
2, Double back the end-of the tube and place it on the large end of the post, If it is necessary to use a tube much smaller than the post, the stretcher simplifies the job.
3. Grease the peeled surface-(if your experience indicates that grease is necessary to make a joint that does not leak).
Mimeo. No. R1158 -7-
4. Unroll the doubled-back portion of the tube and bin. it tightl.
5, Place post on rack.
6. Fasten up loose end of tube.
7. Pour in measured amount of preservative solution.
8. After preservative has all flowed into the wood, remove tube and
place post In storage pile.
Species of 'Vood
Experiments with the tire-tube method thus far do not cover a large
number o 'f species of wood and it is not yet known that all species will take treatment satisfactorily. Good treatments have been obtained at the Forest Products Laboratory in quaking aspen (popple), butternut, American elm, American basswood. black cherry, cottonwood, river birch, jack pine, loblolly pine, soft maple, sweetgum (red gum), tamarack, willow, bitternut and shagbark hickory, and burr,* Northern red, and white oak. Other investigators have reported that sugar maple, red pine, pitch pine, E7astern white pine, Eastern hemlock, black oak, hickory, spruxce,- yellow-poplar, beech, and blackgum are capable of treatment by the method. The results thus far indicate that good treatment can probably be obtained in most species that have a substantial thickness of sapwood.
The results obtained at the Forest Products Laboratory indicate that 10 pounds of a 10 percent zinc chloride solution per cubic foot will result in a satisfactory treatment for quaking aspen (popple), American elm, black cherry,' cottonwood, loblolly pine, river birch, soft maple, tamarack, and will ow.
American basswood, jack pine, and sweetgwn (red gum) appear to require a larger quantity of a weaker solution. The results suggest that 20 pounds of a 5 percent solution per cubic foot will give a satisfactory treatment. Solutions roughly approximating 5 percent in strength can be made by doubling the quantities of water recommended for making 10 percent solutions. For example, a solution of roughly 5 percent can be made by mixing 10-1/2 pounds of 95 percent pure granulated or fused zinc chloride with 180 pounds of water or by adding 80 pounds or 9-1/2 gallons of water to 10 pounds of a 50 percent solution of zinc chloride.
The treatments made on the oaks and hickories showed fairly large
amounts of zinc chloride present in the drip. In order to leave the desired retention of 1. pound per cubic foot in posts of these species an excess of zinc chloride was required to treat them. The results indicated that a satisfactory treatment can be obtained by using about 15 pounds of a 10 percea.t solution per cubic foot but on the average at least one-third of the zinc chloride in the treating solution will be present in the drip. The zinc chloride in the drip should be taken account of In making up additional
Mimeo. No. R1158-8
solution so that the treating costs for posts of these species will not be higher than necessary. A sufficiently reliable method for determining the amount of zinc chloride in the drip consists of obtaining the specific gravity of the drip with a hydrometer, from which the strength of the solution can be determined. ]By multiplying the weight of the drip by its strength the weight of the zinc chloride-is obtained.
The relationship between the specific gravity and strength of zinc chloride solutions for the range most likely to be encountered in the drip when treating the oaks and hickories is given in table 3.
Table 3.--Relationship between specific gravity and strengthaf zinc
Specific gravity at 600 F. Strength of zinc
(as read on the hydrometer) chloride solution
- - - - - - - - - - - - - - - - - - - - - - - -
A very rough method of taking account of the zinc chloride in the
drip does not require a hydrometer, In this method it is assumed that about one-third of the salt in the treating solution will be in the drip. The method can probably best be explained-by an example. Assume that four Oak posts, 7 feet long with average middle diameters of 4, 5-1/2, 6, and 7 inches are to be treated. From table 2 it is found that the quantities of solutions required are 6, 11-1/2, 13-3/4, and 18-3/4 pounds, respectively. Since 15 pounds is recommended for the oaks and hickories these quantities must be increased-by one-half so that 9, 17-1/4, 20-5/8, and 23-1/8 pounds, respectively, or a total of 75 pounds will be required. Ten percent of the total solution, or 7-1/2 pounds will be zinc chloride (10 7- 75 7-1/2).
Mimeo. Nb. R1158 -9-
It is assume& that one-third of the zinc chloride, or 2-1/2. pounds, will be in the drip when the treatment of the posts is completed. Suppose this drip 'is to be used in making up 200 pounds of a 10 percent solution. This quantity of solution would require about 20 pounds of dry zinc chloride and about 180 pounds of water. If the total weight of the drip from the four posts was found to be 30 pounds it is assumed that 27-1/2 pounds of this is water since we have already assumed that 2-1/2 pounds is zinc chloride. By using the drip, 17-1/2 pounds of new zinc chloride (20 minus 2-1/2) and 152-1/2 pounds of water (180 minus 27-1/2) would be required to make 2,00 pounds of a 10 percent solution.
Thickness of Sapwood
Since,, inmost species, the penetration of the preservative is confined almost entirely to the sapwood, the thickness of the sapwood on the posts determines the thickness of the treated zone. It is not known how much influence the thickness of the sapwood will have -upon the life of the treated post. It is considered desirable, however, to have sapwood at least 1 inch thick on 4- to 5- inch diameter posts. On larger posts it is best to havs a wider sapwood 15and, If posts with thinner sapwood than that recommended must be used they will undoubtedly be benefited by the treatment, but possibly not so much as those with thick sapwool. It I--- doubtful that the treatment will be economical on posts with durable heartwood and narrow sapwood.. Such posts give long life without treatment.
Although the penetration of the preservative, in most species, will be limited almost entirely to the aapwood, there may be slight penetration in the exposed heartwood at the ends of the post, especially the and to which the tube is attached. Some preservative may also diffuse into the heartwood in the interior of the post. At the end of the treating period the penetration, even in the sapwood, is likely to be streaked and incomplete$ particularly near the small end of the post. Diffusion of preservative continues after the tube is removed however, as long as the post remains in the green condition, and the preservative will be more uniformly distributed after the posts'are stored for a while than It will be immediately after treatment. It is a good plan, therefore, to allow the bark to remain on the posts for'a week or two, or even longer, after the treatment is finished.
Removal of Bark
If desired, the posts may be set in the ground without removing the bark, but it is believed that longer life will be obtained from posts that
Mimeo. No. R1158 _10-
are peeled before being set, especially that part of the post that will be
above the ground when it is set.
The end of the post to which the tube was attached will be the most thoroughly treated and, therefore, should always be set in the ground.
Coating Ends of Posts
While it is not necessary to coat the exposed wood-it is believed that suitable coatings will be helpful in prolonging the life of the posts. Thick coating of tar, asphalt paint, pitch, or other similar material that will have a moisture retarding effect should reduce the rate at which the preservative is dissolved out of the wood by the water in the soil. If the po sts are peeled before setting in the groun&, the coating may be ap-plied to all the underground parts and to the top end surface,- leaving the remainder uncoated. If the bark is left on, the coating may be applied to the end surfaces and any other spots where bare wood is exposed. Coating the top end of the post should retard the checking of the wood at that point. Such coatings, when used alone, do not preserve the wood from decay, but when used over zinc chloride'treated wood it is believed that they will have a useful effect. It is best to allow the posts to season for a few weeks so that the surfaces become dry before applVing the coatings. Since no records are available thus far on the life of posts without such coatings, in comparison with similar posts coated, it is not possible to say how much increase in life will be obtained by the use of the coatings.
How Long 'Will the Posts Last?
The tire-tube method of treating posts with zinc chloride has not been in use long enough to show the actual life that can be expected from the treated posts. Undoubtedly the life will be different with posts of different species, different sizes, different soils, and in different parts of the country: The life will be longer in comparatively dry soils than in wet soils, and longer in cold climates than in warm climates. The preservative after treatment appears to be better distributed in some woods, such as the pines and oaks, than in woods like aspen and basswood, so that this factor will also influence post life.
From 1937 to 1940 the Forest Products Laboratory treated and placed in service near Madison, Wisconsin, a total of 336 fence posts of various species treated by the tire-tube method. Of 93 aspen and sweetgum posts installed in 1937, 95 percent-of the posts showed some decay but were still serviceable and 5 percent had been removed on account of decay after 7 years service. Of 10 jack pine posts installed in 1938 all were still serviceable after 6 years, although 6 posts showed some decay. From 162 miscellaneous hardwood posts installed in 1939 approximately 80 percent were serviceable and 20 percent were removed on account of decay after 5 years. Another group of 71 miscellaneous hardwoods posts installed during
Mimeo. No. R1158 _11-
1940 showed 94 percent serviceable and 6 percent removed on account of decay after 4 years.
Many of the still serviceable posts in these tests will continue to remain in use for several more years while others are due for early removal. Decay in the posts Is not always confined to the ground line area, many of the posts showing heavier decay in the tops than in the butts. This is an indication of the limited distribution of preservative that can often be expected in a treatment of this type particularly with woods such as aspen and basswood. The results of these limited tests indicate however that tiretube treated posts may have an average life of approximately 10 years which is nearly double the average life that could be expected from untreated posts of the same species. Some of the posts, of course, will last longer than the average while others will rot more quickly. Pine appears to treat better than some of the hardwoods.
It will be helpful if those who use the tire-tube method of treating posts will keep records showing the kind and sizes of the posts, and the date and number installed in different fences. 11ecords should then be made year by year showing the number of treated posts removed and the reason for their removal. Since line fences are seldom disturbed they offer the best opportunity for studying thle length of life obtained from posts.
Other Methods That Can Be Used with Unseasoned Woods
The steeping process is considered to be one of the best methods of applying water-borne preservatives,,such as zinc chloride or chromated zinc chloride,, to green posts or timbers. It has the additional advantage of being adaptable to seasoned or partially seasoned wood. This process consists essentially of soaking the material full length for a period of 1 to
2 weeks in the preservative solution. The principal disadvantage in the method is that it requires a tank of sufficient capacity to hold the posts and preservative. A M1imeograph R621, "Treatment of TLimber by the Steeping Process," obtainable from the Forest Products Laboratory upon request, describes this treatment in greater detail.
Standing trees or freshly felled trees with their branches on cani be treated in the sapwood by adaptations of the Boucherie process worked out by the U. S. Bureau of Entomology and Plant qimrantine, U. S. Department of Agriculture, Beltsville, Maryland. Instructions for making these treatments can be obtained by writing to that Bureau. A description of these methods will also be found in the Journal of Forestry, Vol. 36, No. 1, January 1938.
Mimeo. No. R1158 -12-
The "barrel" method is a simple treatment that is reported by Its users to give satisfactory results on freshly cut pine posts. The posts are treated with the bark on merely by standing theM in a barrel or trough of preservative solution. After treatment the posts are allowed to stand with the treated. end up and season before being set. Instructions for treating posts by the barrel method are given in Circular 262, "Longer Life for Fence Posts9ft obtainable upon request from Clemson Agricultural College, Clemson, South Carolina.
Mimeo. No. R1158
Figure 1.--Tire-tube method of treating fence posts. z 32857 7
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