Wood Fungi Solution

Pressure Treatment Process

Pressure treatment process

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Wood Preservation study

Ref- Various sources

Wood is treated with preservatives to protect it from wood-destroying fungi and insects. Treating wood with preservative chemicals can increase the service life of wood by a factor of five times or more. Wood treated with commonly used wood preservatives can last 40 years or more in service. Preservative-treated wood (figure 1) is an economical, durable, and aesthetically pleasing building material and is a natural choice for many construction projects in the national forests. When treated wood is used in field settings, the possibility of environmental contamination raises concerns. There is increasing pressure to be environmentally friendly and to reduce, restrict, or eliminate the use of wood preservatives because of the concern that toxic constituents may leach from the treated wood. This report will provide an overview of preservative systems, help readers understand the level of risk and status of the science involved in evaluating preservative systems, and provide some guidelines for using the product .

Wood preservatives have been used for more than a century. They are broadly classified as either waterborne or oil-type, based on the chemical composition of the preservative and the carrier used during the treating process. Some preservatives can be formulated for use with either water or oil solvents. Water-based preservatives often include some type of cosolvent, such as amine or ammonia to keep one or more of the active ingredients in solution. Each solvent has advantages and disadvantages that depend on the application. Generally, wood preservatives also are classified or grouped by the type of application or exposure environment in which they are expected to provide long term protection. Some preservatives have sufficient leach resistance and broad spectrum efficacy to protect wood that is exposed directly to soil and water. These preservatives will also protect wood exposed aboveground, and may be used in those applications at lower retentions (concentrations in the wood)

Other preservatives have intermediate toxicity or leach resistance that allows them to protect wood fully exposed to the weather, but not in contact with the ground. Some preservatives lack the permanence or toxicity to withstand continued exposure to precipitation, but may be effective with occasional wetting. Finally, there are formulations that are so readily leachable that they can only withstand very occasional, superficial wetting. It is not possible to evaluate a preservative’s long term efficacy in all types of exposure environments and there is no set formula for predicting exactly how long a wood preservative will perform in a specific application. This is especially true for aboveground applications because preservatives are tested most extensively in ground contact. To compensate for this uncertainty, there is a tendency to be conservative in selecting a preservative for a particular application.

Oil-Type Preservatives

The most common oil-type preservatives are creosote, pentachlorophenol, and copper naphthenate. Occasion-ally, oxine copper and IPBC (3-iodo-2-propynyl butyl carbamate) also are used for aboveground applications. The conventional oil-type preservatives, such as creosote and pentachlorophenol solutions, have been confined largely to uses that do not involve frequent human contact. The exception is copper naphthenate, a preservative that was developed more recently and has been used less widely. Oil-type preservatives may be visually oily, or oily to the touch, and sometimes have a noticeable odor. However, the oil or solvent that is used as a carrier makes the wood less susceptible to cracks and checking. This type of preservative is suitable for treatment of glue-laminated stringers for bridges where cracks in the stringers could alter the bridges’ structural integrity

Creosote

 Coal-tar creosote is effective when used in ground contact, water contact, or aboveground. It is the oldest wood preservative still in commercial use in the United States. It is made by distilling coal tar that is created when coal is carbonized at high temperatures (1,652 to 2,192 degrees Fahrenheit [900 to 1,200 degrees Celsius]). Unlike other oil-type preservatives, creosote usually is not dissolved in oil, but it does look and feel oily. Creosote contains a chemically complex mixture of organic molecules, most of which are polycyclic aromatic hydrocarbons. The composition of creosote varies because it depends on how the creosote is distilled. However, the small differences in composition in modern creosotes do not affect their performance as wood preservatives. Creosote-treated wood is dark brown to black and has a distinct odor, which some people consider unpleasant. Creosote-treated wood is very difficult to paint. Workers sometimes object to creosote-treated wood because it soils their clothes and makes their skin sensitive to the sun. The treated wood sometimes has an oily surface. Patches of creosote sometimes accumulate, creating a hazard when it contacts the skin. Because of these concerns, creosote-treated wood often is not the first choice for applications such as bridge members or handrails, where there is a high probability of human contact. However, creosote-treated wood has advantages to offset concerns with its appearance and odor. It has a lengthy record of satisfactory use in a wide range of applications and is relatively inexpensive. Creosote is effective in protecting both hardwoods and softwoods and improving the dimensional stability of the treated wood. Creosote is listed in American Wood-Preservers’ Association (AWPA) Standards for a wide range of wood products created from many different species of trees. The minimum creosote retentions required by the standards are in the range of 5 to 8 pounds per cubic foot (80 to 128 kilograms per cubic meter) for aboveground applications, 10 pounds per cubic foot (160 kilograms per cubic meter) for wood used in ground contact, and 12 pounds per cubic foot (192 kilograms per cubic meter) for wood used in critical structural applications, such as highway construction. With heated solutions and lengthy pressure periods, creosote can penetrate wood that is fairly difficult to treat. Creosote is suitable for treatment of glue-laminated members. Creosote treatment does not accelerate, and may even inhibit, the corrosion of metal fasteners. Treatment facilities that use creosote are found throughout the United States, so this wood preservative is readily available. Creosote is classified as a Restricted Use Pesticide (RUP) by the U.S. Environmental Protection Agency (EPA). Producers of treated wood, in cooperation with the EPA, have created Consumer Information Sheets with guidance on appropriate handling and site precautions when using wood treated with creosote . These sheets should be available for all persons who handle creosote-treated wood.

Pentachlorophenol

Pentachlorophenol has been widely used as a pressure-treatment preservative in the United States since the 1940s. The active ingredients, chlorinated phenols, are crystalline solids that can be dissolved in different types of organic solvents. A performance of pentachlorophenol and the properties of the treated wood are influenced by the properties of the solvent. Pentachlorophenol is effective when used in ground contact, freshwater, or aboveground. It is not as effective when used in seawater. A heavy oil solvent (specified as Type A in AWPA Standard P9) is preferable when the treated wood is to be used in ground contact. Wood treated with lighter solvents may not be as durable. Wood treated with pentachlorophenol in heavy oil typically has a brown color, and may have a slightly oily surface that is difficult to paint. It also has some odor, which is associated with the solvent. Pentachlorophenol in heavy oil should not be used when frequent contact with skin is likely (handrails, for instance). Pentachlorophenol in heavy oil has long been a popular choice for treating utility poles, bridge timbers, glue-laminated beams, and foundation pilings. The effectiveness of pentachlorophenol is similar to that of creosote in protecting both hardwoods and softwoods, and pentachlorophenol often is thought to improve the dimensional stability of the treated wood. Pentachlorophenol is listed in the AWPA standards for a wide range of wood products and wood species. The minimum softwood retentions are 0.4 pounds per cubic foot (6.4 kilograms per cubic meter) for wood used aboveground, and 0.5 pounds per cubic foot (8 kilograms per cubic meter) for wood used in critical structural applications or in ground contact. With heated solutions and extended pressure periods, pentachlorophenol can penetrate woods that are difficult to treat. Pentachlorophenol does not accelerate the corrosion of metal fasteners relative to untreated wood. The heavy oil solvent imparts some water repellency to the treated wood. Treatment facilities in many areas of the United States use pentachlorophenol in heavy oil, making it another readily available wood preservative. Pentachlorophenol is most effective when applied with a heavy solvent, but it performs well in lighter solvents for aboveground applications. Lighter solvents also provide the advantage of a less oily surface appearance, lighter color, and improved paintability. The standards for aboveground minimum retentions for pentachlorophenol vary from 0.25 to 0.3 pounds per cubic foot (4 to 4.8 kilograms per cubic meter) for treatment of red oak to 0.4 pounds per cubic foot (6.4 kilograms per cubic meter) for softwood species. Pentachlorophenol in light oil has some similarities to pentachlorophenol in heavy oil. It can be used to treat species of wood that are difficult to treat and it does not accelerate corrosion. Wood treated with pentachlorophenol in light oil may be used in recreational structures and in applications where human contact is likely, such as handrails, if a sealer such as urethane, shellac, latex, epoxy enamel, or varnish is applied. Wood treated with pentachlorophenol in light oil may be painted or stained after it dries. One disadvantage of the lighter oil is that the treated wood has less water repellency. Treatment facilities that use pentachlorophenol in light oil are not as numerous as those that use heavy oil. Pentachlorophenol is classified as an RUP by the EPA. Producers of treated wood, in cooperation with the EPA, have created consumer information sheets with guidance on appropriate handling and site precautions for wood treated with pentachlorophenol (appendix A). These sheets should be available for all persons who handle wood treated with pentachlorophenol. Pentachlorophenol Pentachlorophenol has been widely used as a pressure-treatment preservative in the United States since the 1940s. The active ingredients, chlorinated phenols, are crystalline solids that can be dissolved in different types of organic solvents. A performance of pentachlorophenol and the properties of the treated wood are influenced by the properties of the solvent. Pentachlorophenol is effective when used in ground contact, freshwater, or aboveground. It is not as effective when used in seawater. A heavy oil solvent (specified as Type A in AWPA Standard P9) is preferable when the treated wood is to be used in ground contact. Wood treated with lighter solvents may not be as durable. Wood treated with pentachlorophenol in heavy oil typically has a brown color, and may have a slightly oily surface that is difficult to paint. It also has some odor, which is associated with the solvent. Pentachlorophenol in heavy oil should not be used when frequent contact with skin is likely (handrails, for instance). Pentachlorophenol in heavy oil has long been a popular choice for treating utility poles, bridge timbers, glue-laminated beams, and foundation pilings. The effectiveness of pentachlorophenol is similar to that of creosote in protecting both hardwoods and softwoods, and pentachlorophenol often is thought to improve the dimensional stability of the treated wood. Pentachlorophenol is listed in the AWPA standards for a wide range of wood products and wood species. The minimum softwood retentions are 0.4 pounds per cubic foot (6.4 kilograms per cubic meter) for wood used aboveground, and 0.5 pounds per cubic foot (8 kilograms per cubic meter) for wood used in critical structural applications or in ground contact.

Copper Naphthenate

 Copper naphthenate is effective when used in ground contact, water contact, or aboveground. It is not standardized for use in saltwater applications. Copper naphthenate effectiveness as a preservative has been known since the early 1900s, and various formulations have been used commercially since the 1940s. It is an organometallic compound formed as a reaction product of copper salts and naphthenic acids derived from petroleum. Unlike other commercially applied wood preservatives, small quantities of copper naphthenate can be purchased at retail hardware stores and lumberyards. Cuts or holes in treated wood can be treated in the field with copper naphthenate. Wood treated with copper naphthenate has a distinctive bright green color that weathers to light brown. The treated wood also has an odor that dissipates somewhat over time. Depending on the solvent used and treatment procedures, it may be possible to paint wood treated with copper naphthenate after it has been allowed to weather for a few weeks. Copper naphthenate can be dissolved in a variety of solvents. The heavy oil solvent (specified in AWPA Standard P9, Type A) or the lighter solvent (AWPA Standard P9, Type C) are the most commonly used. Copper naphthenate is listed in AWPA standards for treatment of major softwood species that are used for a variety of wood products. It is not listed for treatment of any hardwood species, except when the wood is used for railroad ties. The minimum copper naphthenate retentions (as elemental copper) range from 0.04 pounds per cubic foot (0.6 kilograms per cubic meter) for wood used aboveground, to 0.06 pounds per cubic foot (1 kilograms per cubic meter) for wood that will contact the ground and 0.075 pounds per cubic foot (1.2 kilograms per cubic meter) for wood used in critical structural applications. When dissolved in No. 2 fuel oil, copper naphthenate can penetrate wood that is difficult to treat. Copper naphthenate loses some of its ability to penetrate wood when it is dissolved in heavier oils. Copper naphthenate treatments do not significantly increase the corrosion of metal fasteners relative to untreated wood. Copper naphthenate is commonly used to treat utility poles, although fewer facilities treat utility poles with copper naphthenate than with creosote or pentachlorophenol. Unlike creosote and pentachlorophenol, copper naphthenate is not listed as an RUP by the EPA. Even though human health concerns do not require copper naphthenate to be listed as an RUP, precautions such as the use of dust masks and gloves should be used when working with wood treated with copper naphthenate.

Oxine Copper (Copper-8-Quinolinolate)

Oxine copper is effective when used aboveground. Its efficacy is reduced when it is used in direct contact with the ground or with water. It has not been standardized for those applications. Oxine copper (copper-8-quinolinolate) is an organometallic compound. The formulation consists of at least 10-percent copper-8-quinolinolate, 10-percent nickel-2-ethylhexanoate, and 80-percent inert ingredients. It is accepted as a standalone preservative for aboveground use to control sapstain fungi and mold and also is used to pressure-treat wood. Oxine copper solutions are greenish brown, odorless, toxic to both wood decay fungi and insects, and have a low toxicity to humans and animals. Oxine copper can be dissolved in a range of hydrocarbon solvents, but provides protection much longer when it is delivered in heavy oil. Oxine copper is listed in the AWPA standards for treating several softwood species used in exposed, aboveground applications. The minimum specified retention for these applications is 0.02 pounds per cubic foot (0.32 kilograms per cubic meter, as elemental copper).

IPBC and Insecticides

 IPBC (3-iodo-2-propynyl butyl carbamate) is not intended for use in ground contact or for horizontal surfaces that are fully exposed to the weather. It does provide protection for wood that is aboveground and partially protected from the weather3

Some pressure-treating facilities use a mixture of IPBC and an insecticide, such as permethrin or chlorpyrifos, to treat structural members used above ground that will be largely protected from the weather, although this practice is not a standardized treatment. These facilities are using IPBC retentions of 0.035 pounds per cubic foot (0.56 kilograms per cubic meter) or higher, with mineral spirits as the solvent. The advantage of this treatment is that it is colorless and allows the wood to maintain its natural appearance. This treatment is being used on Western species that are difficult to treat. Very few facilities are conducting pressure treatments with IPBC

Alkaline Copper Quaternary (ACQ)

 Compounds Alkaline copper quat (ACQ) is one of the best  wood preservatives that have been developed in recent years to meet market demands for alternatives to CCA. The fungicides and insecticides in ACQ are copper oxide (67 percent) and a quaternary ammonium compound (quat). 

Many variations of ACQ have been standardized or are being standardized. ACQ type B (ACQ–B) is an ammoniacal copper formulation, ACQ type D (ACQ–D) is an amine copper formulation, and ACQ type C (ACQ–C) is a combined ammoniacal-amine formulation with a slightly different quat compound. Wood treated with ACQ–B is dark greenish brown and fades to a lighter brown. It may have a slight ammonia odor until the wood dries. Wood treated with ACQ–D has a lighter greenish-brown color and has little noticeable odor; wood treated with ACQ–C varies between the color of ACQ–B and that of ACQ–D, depending on the formulation. Stakes treated with these three formulations have demonstrated their effectiveness against decay fungi and insects when the stakes contacted the ground. 

The ACQ formulations are listed in the AWPA standards for a range of applications and many softwood species. The listings for ACQ–C are limited because it is the most recently standardized. 

The minimum ACQ retentions are 0.25 pounds per cubic foot (4 kilograms per cubic meter) for aboveground applications, 0.4 pounds per cubic foot (6.4 kilograms per cubic meter) for applications involving ground contact, and 0.6 pounds per cubic foot (9.6 kilo-grams per cubic meter) for highway construction. The different formulations of ACQ allow some flexibility in achieving compatibility with a specific wood species and application. An ammonia carrier improves the ability of ACQ to penetrate into wood that is difficult to treat. For wood species that are easier to treat, such as southern pine, an amine carrier will provide a more uniform surface appearance.

All ACQ treatments accelerate corrosion of metal fasteners relative to untreated wood. Hot-dipped galvanized copper or stainless steel fasteners must be used. The number of pressure-treatment facilities using ACQ is increasing. In the Western United States, the ACQ–B formulation is used because it will penetrate difficult to treat Western species better than other waterborne preservatives. Treatment plants elsewhere generally use the ACQ–D formulation. Researchers at the USDA Forest Service’s Forest Products Laboratory in Madison, WI, are evaluating the performance of a secondary highway bridge constructed using Southern pine lumber treated with ACQ–D (Ritter and Duwadi 1998).

Borates

Borate compounds are the most commonly used unfixed waterborne preservatives. Unfixed preservatives can leach from treated wood. They are used for pressure treatment of framing lumber used in areas with high termite hazard and as surface treatments for a wide range of wood products, such as cabin logs and the interiors of wood structures. They are also applied as internal treatments using rods or pastes. At higher rates of retention, borates also are used as fire-retardant treatments for wood. Boron has some exceptional performance characteristics, including activity against fungi and insects, but low mammalian toxicity. It is relatively inexpensive. Another advantage of boron is its ability to diffuse with water into wood that normally resists traditional pressure treatment. Wood treated with borates has no added color, no odor, and can be finished (primed and painted). While boron has many potential applications in framing, it probably is not suitable for many Forest Service applications because the chemical will leach from the wood under wet conditions. It may be a useful treatment for insect protection in areas continually protected from water. Inorganic boron is listed as a wood preservative in the AWPA standards, which include formulations prepared from sodium octaborate, sodium tetraborate, sodium pentaborate, and boric acid. Inorganic boron is also standardized as a pressure treatment for a variety of species of softwood lumber used out of contact with the ground and continuously protected from water. The minimum borate (B2O3) retention is 0.17 pounds per cubic foot (2.7 kilograms per cubic meter). A retention of 0.28 pounds per cubic foot (4.5 kilograms per cubic meter) is specified for areas with Formosan subterranean termites. Borate preservatives are available in several forms, but the most common is disodium octaborate tetrahydrate (DOT). DOT has higher water solubility than many other forms of borate, allowing more concentrated solutions to be used and increasing the mobility 11 of the borate through the wood. With the use of heated solutions, extended pressure periods, and diffusion periods after treatment, DOT can penetrate species that are relatively difficult to treat, such as spruce. Several pressure treatment facilities in the United States use borate solutions. Although borates have low mammalian toxicity, workers handling borate-treated wood should use standard precautions, such as wearing gloves and dust masks. The environmental impact of borate-treated wood for construction projects in sensitive areas has not been evaluated. Because borate-treated wood is used in areas protected from precipitation or water, little or no borate should leach into the environment. Borates have low toxicity to birds, aquatic invertebrates, and fish. Boron occurs naturally at relatively high levels in the environment. Because borates leach readily, extra care should be taken to protect borate-treated wood from precipitation when it is stored at the jobsite. Precipitation could deplete levels of boron in the wood to ineffective levels and harm vegetation directly below the stored wood. Borate-treated wood should be used only in applications where the wood is kept free from rainwater, standing water, and ground contact

Treatment Processes

Methods that preserve wood generally are either:

• Pressure processes, in which the wood is impregnated in closed vessels at pressures considerably higher than atmospheric pressure

• Processes that do not involve pressure

Pressure Processes

In commercial practice, wood usually is treated by immersing it in preservative in an apparatus that applies high pressure, driving the preservative into the wood. Pressure processes differ in details, but the general principle is the same. The wood is carried on cars or trams into a long steel cylinder, which is closed and filled with preservative. Pressure forces the preservative into the wood until the desired amount has been absorbed and has penetrated relatively deeply. Commonly, three general pressure processes are used: full cell, modified full cell, and empty cell. Commercial treaters often use variations or combinations of these processes. Full-Cell Processes The full-cell (Bethel) process is used when the goal is for wood to retain as much of the preservative as possible. For instance, it is a standard procedure to treat timbers with creosote using the full-cell process to protect the timbers from marine borers. Waterborne preservatives sometimes are applied by the full-cell process. Preservative retention can be controlled by regulating the concentration of the treating solution. The steps in the full-cell process are: 1.Wood is sealed in the treatment cylinder and a preliminary vacuum is applied for a half an hour or longer to remove the air from the cylinder and as much air as possible from the wood.

2.The preservative (at ambient temperature or higher, depending on the system) is pumped into the cylinder without breaking the vacuum.

3.After the cylinder is filled, pressure is applied until the wood will take no more preservative or until the required retention of preservative has been achieved.

4.After pressure has been applied for the specified time, the preservative is pumped from the cylinder.

5.A short final vacuum may be used to remove dripping preservative from the wood

Modified Full-Cell Processes

The modified full-cell process is basically the same as the full-cell process except that it uses lower levels of initial vacuum and often uses an extended final vacuum. The amount of initial vacuum is determined by the wood species, material size, and retention desired. Residual air in the wood expands during the final vacuum to drive out part of the injected preservative solution. For this reason, modified full-cell schedules are sometimes called low-weight schedules. They are now the most common method of treating wood with waterborne preservatives. Empty-Cell Processes The empty-cell process is designed to obtain deep penetration with a relatively low net retention of preservative. The empty-cell process should always be used for treatment with oil preservatives if it provides the desired retention. Two empty-cell processes, the Rueping and the Lowry, are commonly employed; both use the expansive force of compressed air to drive out part of the preservative absorbed during the pressure period. The Rueping empty-cell process, often called the empty-cell process with initial air, has been widely used for many years in Europe and the United States. The following general procedure is employed:

 1.Air under pressure is forced into the treatment cylinder, which contains the wood. The air penetrates some species easily, requiring just a few minutes of application pressure. In treating the more resistant species, the common practice is to maintain air pressure from half an hour to 1 hour before pumping in the preservative, although the need to maintain air pressure for longer than a few minutes does not seem to be fully established. The air pressures employed generally range between 25 to 100 pounds per square inch (172 to 689 kilopascals), depending on the net retention of preservative desired and the resistance of the wood.

2.After the period of preliminary air pressure, preservative is forced into the cylinder. As the preservative is pumped in, air escapes from the treatment cylinder into an equalizing tank (also known as a Rueping tank) at a rate that keeps the pressure constant in the cylinder. When the treatment cylinder is filled with preservative, the treatment pressure is increased above the initial air pressure and is maintained until the wood absorbs no more preservative, or until enough preservative has been absorbed for the required retention of preservative.

3.At the end of the pressure period, the preservative is drained from the cylinder, and surplus preservative is removed from the wood with vacuum. From 20 to 60 percent of the total preservative injected into the cylinder can be recovered after the vacuum has been applied.

Treating Pressures and Preservative Temperatures

The pressures used in treatments vary from about 50 to 250 pounds per square inch (345 to 1,723 kilopascals), depending on the species and the ease with which the wood takes the treatment; pressures commonly range from about 125 to 175 pounds per square inch (862 to 1,207 kilopascals). Many woods are sensitive to (and could be damaged by) high treatment pressures. Heated preservatives are used sometimes to improve penetration, but the elevated temperatures can affect the wood’s properties and the stability of the treatment solution. The AWPA specifications require that the temperature of the preservative during the entire pressure period not exceed 120 degrees Fahrenheit (49 degrees Celsius) for ACC and CCA and 150 degrees Fahrenheit (60 degrees Celsius) for ACQ–B, ACQ–D, ACZA, CBA–A, CA–B, and CDDC. The maximum temperature for inorganic boron is 200 degrees Fahrenheit (93 degrees Celsius). Please refer to the Wood Handbook for more information on treating pressures and temperatures. Penetration and Retention Penetration and retention requirements are equally important in determining the quality of preservative treatment. Penetration levels vary widely, even in pressure-treated material. In most species, heartwood is more difficult to penetrate than sapwood. In addition, species differ greatly in the degree to which their heartwood may be penetrated. Incising (perforating the surface of the wood with small slits) tends to improve the penetration of preservative in many refractory species, but species that are highly resistant to penetration will not have deep or uniform penetration, even when they are incised. When the heart faces of these species are not incised, penetration may be as deep as 1⁄ 4 inch (6 millimeters), but often is not more than 1⁄ 16 inch (1.6 millimeters).

Non pressure Processes

The numerous non pressure processes differ widely in the penetration and retention levels that may be achieved and in the degree of protection they provide. When similar retention and penetration levels are reached, the service life of wood treated by a non pressure method should be comparable to that of wood treated by a process that uses pressure. Nevertheless, non pressure treatments, particularly those involving surface applications, generally do not produce results as satisfactory as those produced by pressure treatments. The non pressure processes do serve a useful purpose when more thorough treatments are impractical or when little protection is required.

In general, non pressure methods consist of:

• Surface application of preservatives by brushing or brief dipping

 • Soaking wood in preservative oils or steeping it in solutions of waterborne preservatives

• Diffusion processes using waterborne preservatives

• Vacuum treatment

 • Other miscellaneous processes 

Surface Applications The simplest treatment is to dip wood into preservative or to brush preservative on the wood. Preservatives that have low viscosity when cold should be used, unless the preservative can be heated. The preservative should be flooded over the wood rather than merely painted. Every check and depression in the wood should be thoroughly filled with the preservative. Any untreated wood that is left exposed will provide ready access for fungi. Rough lumber may require as much as 10 gallons of oil per 1,000 square feet (40 liters of oil per 100 square meters) of surface. 

Surfaced lumber requires considerably less oil. The transverse penetration usually will be less than 1⁄ 10 inch (2.5 millimeters), although in easily penetrated species, end-grain (longitudinal) penetration will be considerably deeper. The additional life obtained by such treatments will be affected greatly by the conditions of service. For treated wood that contacts the ground, service life may be from 1 to 5 years. Dipping wood for a few seconds to several minutes in a preservative provides more assurance that all surfaces and checks will be thoroughly coated with the preservative. In addition, dipping usually produces slightly deeper penetration. Window sashes, frames, and other millwork commonly are treated by dipping them in a water-repellent preservative, either before or after assembly. Transverse penetration of the preservative applied by brief dipping is very shallow, usually less than a few hundredths of an inch (a millimeter). The exposed end surfaces at joints are the most vulnerable to decay in millwork products. Good end-grain penetration is especially important. Dip applications provide very limited protection to wood that contacts the ground or that is used in very moist conditions. They provide very limited protection against attack by termites. However, they do have value for exterior woodwork and millwork that is painted, that does not contact the ground, and that is exposed to moisture just for brief periods.

Thermal process treatment consists of immersing wood alternately in separate tanks containing heated and cold preservative, either oil- or waterborne (or in one tank which is first heated than allowed to cool). During the hot bath, air in the wood expands and some is forced out. Heating improves penetration of preservatives. In the cold bath, air in the wood contracts, creating a partial vacuum, and atmospheric pressure forces more preservative into the wood. Temperature is critical; only use preservatives that can safely be heated.

Wood Preservation: Wood Enemies - Wood Fungi

Wood Preservation: Wood Enemies - Wood Fungi: Wood decay Fungus Wood decay Fungus Brown Rot Brown-rot fungi break down  hemicellulose  and  cellulose  that form the wood...

Wood Enemies - Wood Fungi

Wood decay Fungus

Wood decay Fungus

Brown Rot

Brown-rot fungi break down hemicellulose and cellulose that form the wood structure. Cellulose is broken down by hydrogen peroxide (H₂O₂) that is produced during the breakdown of hemicellulose. Because hydrogen peroxide is a small molecule, it can diffuse rapidly through the wood, leading to a decay that is not confined to the direct surroundings of the fungal hyphae. As a result of this type of decay, the wood shrinks, shows a brown discoloration, and cracks into roughly cubical pieces, a phenomenon termed cubical fracture. The fungi of certain types remove cellulose compounds from wood and hence the wood becomes brown colour.

Brown rot in a dry, crumbly condition is sometimes incorrectly referred to as dry rot in general. The term brown rot replaced the general use of the term dry rot, as wood must be damp to decay, although it may become dry later. Dry rot is a generic name for certain species of brown-rot fungi.

Brown-rot fungi of particular economic importance include Serpula lacrymans (true dry rot), Fibroporia vaillantii (mine fungus), and Coniophora puteana (cellar fungus), which may attack timber in buildings. Other brown-rot fungi include the sulfur shelf, Phaeolus schweinitzii, and Fomitopsis pinicola.

Brown-rot fungal decay is characterised by extensive demethylation of lignins whereas white-rot tends to produce low yields of molecules with demethylated functional groups.

t

 Soft rot

Soft-rot fungi secrete cellulase from their hyphae, an enzyme that breaks down cellulose in the wood. This leads to the formation of microscopic cavities inside the wood, and sometimes to a discoloration and cracking pattern similar to brown rot.^[4][5] Soft-rot fungi need fixed nitrogen in order to synthesize enzymes, which they obtain either from the wood or from the environment. Examples of soft-rot-causing fungi are Chaetomium, Ceratocystis, and Kretzschmaria deusta.

Soft-rot fungi are able to colonise conditions that are too hot, cold or wet for brown or white-rot to inhabit. They can also decompose woods with high levels of compounds that are resistant to biological attack. Bark in woody plants contains a high concentration of tannin, which is difficult for fungi to decompose, and suberin which may act as a microbial barrier. The bark acts as form of protection for the more vulnerable interior of the plant. Soft-rot fungi do not tend to be able to decompose matter as effectively as white-rot fungi: they are less aggressive decomposers

White Rot

White-rot fungi break down the lignin in wood, leaving the lighter-colored cellulose behind; some of them break down both lignin and cellulose. As a result, the wood changes texture, becoming moist, soft, spongy, or stringy; its colour becomes white or yellow. Because white-rot fungi are able to produce enzymes, such as laccase, needed to break down lignin and other complex organic molecules, they have been investigated for use in mycoremediation applications.

There are many different enzymes that are involved in the decay of wood by white-rot fungi, some of which directly oxidize lignin. The relative abundance of phenylpropane alkyl side chains of lignin characteristically decreases when decayed by white-rot fungi. It has been reported that the oyster mushroom (Pleurotus ostreatus) preferentially decays lignin instead of polysaccharides. This is different from some other white-rot fungi, e.g., Phanerochaete chrysosporium, which shows no selectivity to lignocellulose.

 Other white-rot fungi include the turkey tail, artist's conk, and tinder fungus.

White-rot fungi are grown all over the world as a source of food .

Blue stain Fungi

Blue stain fungi (also known as sap stain fungi) is a vague term including various fungi that cause dark staining in sapwood. The staining is most often blue, but could also be grey or black

Wood Fungi Problem

Wood Enemies- Wood Borers

Wood borers or common furniture beetles

The common furniture beetle or common house borer is a wood boring beetle.
In the larva stage it bores in wood and feeds upon it.
Adults do not feed; they just reproduce. The female lays her eggs into cracks in wood or inside old exit holes, if available. The eggs hatch after some three weeks, each producing a 1 mm long, creamy white, C-shaped larva. For three to four years the larvae bore semi-randomly through timber, following and eating the starchy part of the wood grain, and grow up to 7 mm. They come nearer to the wood surface when ready to pupate. They excavate small spaces just under the wood surface and take up to eight weeks to pupate. The adults then break through to the surface as adults, making a 1mm to 1.5 mm exit hole and spilling dust, the first visible signs of an infestation.
Borers only attacks seasoned sapwood timber, not live or fresh wood. Also, it usually does not attack heartwood of the timbers. This is readily observed from infested structures, where one piece of timber may be heavily attacked but an adjacent one left virtually untouched according to whether it is made from the heartwood or the sapwood part of a tree trunk. Infestations are also usually a problem of old wooden houses built with untreated timbers. Some building regulations state that timbers with more than 25% sapwood may not be used, so that wood borer infections can not substantially weaken structures.
Infection, past or present, is diagnosed by small round exit holes of 1 to 1.5 mm diameter. Active infections feature the appearance of new exit holes and fine wood dust around the holes.

Some types of wood borers

Wood Enemies - Termites

Below are major wood enemies due to their presence service life of wood is decreased notably.

Termites

Queen lives in ground up to 20 feet deep.  Workers tunnel to surface under a piece of wood and start eating it.

If they can't reach wood from ground, they build tubes of dirt up to the wood.  Some tubes are self-supporting and reach up to 2 feet.  Others are attached to other structure such as block wall and have been known to go up 8 feet to reach wood.

Termites never work in the open.  Always in wood or tubes.

There are only two types of homes in the world  those with termites and those that are going to get termites.

Termites are a group of insects consisting of 2,500 species of which 300 are considered pests. Termites are one of the most damaging pests in the tropics and can cause considerable problems in housing.

There are 2500 species of termites including subterranean termites, Thompson termites ,Termopsidae,  hototermitidae, kalotermitidae, seritermitidae, etc. 

There are several families and sub-families. Some have nests underground, others in wood, for example hollow trees, and some build mounds. 

Termites are causing severe damages to buildings and constructions and structures all over the world and now a days it is a great problem to the industry.

Termites feed on cellulose, paper, plywood, cloths, bamboo, furniture, wood etc.Which are prone and very sensitive for termite attacks.

Besides  making tiny ways through the walls and structures, making the structure weak.

Termites enter through the foundation. Hence, it is most important to have preventive measures. 

Facts about Termites:

Live for 15 years and lay 1 egg every 15 seconds

Have 4 wings

Burrow tiny mud tunnels to a source of wood

Leave sawdust near windows

Enjoy wood resulting from leaky plumbing

Termites  might be in your home actually live 15-25 feet underground, and perhaps as far as 50 yards or more from your building.

Can destroy entire house in about 4-5 years in USA

A typical termite colony can number 300,000 to 3,000,000 workers.  Think in terms of a 200 ltrs drum full of squirming grains of rice… that’s a small colony.

Hence, it is very necessary to protect wood from termites.

How to keep wooden furniture away from wood borers

How to keep wooden furniture away from wood borers

Why Copper

Copper is an essential micronutrient for most living cells. In larger doses though, the copper ion demonstrates activity as an algaecide, bactericide, fungicide, insecticide, and moldicide. Presently copper compounds are used for algal control, wood treatment, antifouling pigments, and crop fungicides (Richardson 1997). The fungicidal properties of copper were recognized in the 1700s, and copper-based preservatives have been widely and successfully used for more than a century. Although borates and organic biocides are gaining importance, copper remains the primary biocide component used today to protect wood used in ground contact or fully exposed to the weather (Lebow et al. 2004). Copper is needed against this challenge since very few organic molecules (other than creosote and penta) possess activity towards soft rot fungi (Hughes 2004). The volume of wood products treated with copper-based preservatives grew exponentially during the 1970s and 1980s and remains high today. Copper compounds also have advantages: it is relatively easy to create waterborne formulations; it is easy to analyze and determine penetration in wood, and copper slows photodegradation by UV radiation and water (Archer and Preston 2006). The focus on copper-based preservatives has increased following concerns about environmental effects of chromium and arsenic and resulting restrictions on the use of chromated copper arsenate (CCA). Much of the early work on copper-based formulations forms the basis for the ammoniacal and amine copper-based systems currently in the marketplace as CCA replacements (Preston et al. 1985). These formulations include quats or azoles as co-biocides. Recently micronized copper formulations with the same co-biocides have come into use. The drawbacks on use of copper compounds include: copper tolerance exhibited in a number of fungal species, possible corrosivity to metal fasteners and aquatic toxicity (Archer and Preston 2006). This paper presents a discussion on copper issues such as the mode of action, problems of copper tolerance, replacements for CCA, the latest micronized formulations and environmental effects of copper-based preservatives.

Copper Azole

Copper azole preservative (denoted as CA-B and CA-C under American Wood Protection Association (AWPA) standards) is a major copper based wood preservative that has come into wide use in the USA, Europe, Japan and Australia following restrictions on CCA. Its use is governed by national and international standards, which determine the volume of preservative uptake required for a specific timber end use.

Copper Azole is similar to ACQ with the difference being that the dissolved copper preservative is augmented by an Azole co-biocide instead of the quat biocide used in ACQ. The Azole co-biocide yields a Copper Azole product that is effective at much lower retentions than required for equivalent ACQ performance.

It is marketed widely under the "Wolmanized" brand in the US, and the "Tanalith" brand across Europe and other international markets.

The AWPA standard retention for CA-B is .10 pounds per cubic ft (pcf) for above ground applications and .21 pcf for ground contact applications. Type C copper azole, denoted as CA-C, has been introduced under the Wolmanized brand. The AWPA standard retention for CA-C is .06 pounds per cubic ft (pcf) for above ground applications and .15 pcf for ground contact applications.

The copper azole preservative incorporates organic triazoles such as tebuconazole or propiconazole as the co-biocide, which are also used to protect food crops. The general appearance of wood treated with copper azole preservative is similar to CCA with a green colouration.


Other copper compounds
These include copper HDO (CuHDO), copper chromate, copper citrate, acid copper chromate and ammoniacal copper zinc arsenate (ACZA). The CuHDO treatment is an alternative to CCA, ACQ and CA used in Europe and in approval stages for United States and Canada. ACZA is generally used for marine applications.

New Generation ACQ

Alkaline copper quaternary
Alkaline copper quaternary (ACQ) is a preservative made up of copper, a fungicide, and a quaternary ammonium compound (quat), an insecticide which also augments the fungicidal treatment is a wood preservative that has come into wide use in the USA, Europe, Japan and Australia following restrictions on CCA. Its use is governed by national and international standards, which determine the volume of preservative uptake required for a specific timber end use.

Since it contains high levels of copper, ACQ-treated timber is five times more corrosive to common steel, according to test results. It is necessary to use double-galvanized or stainless steel fasteners in ACQ timber. Use of fasteners meeting or exceeding requirements for ASTM A 153 Class D meet the added requirements for fastener durability. The U.S. began mandating the use of non-arsenic containing wood preservatives for virtually all residential use timber in 2004.

Modern versions have been developed which offer improved performance to those mentioned above. It should be noted that the American Wood Protection Association (AWPA) standards for ACQ require a retention of 0.25 pounds per cubic ft (PCF) for above ground use and .40 pcf for ground contact.

ACA

Ammoniacal Copper Arsenate (ACA): water-borne fixing type:
The formulation consists of copper sulphate and arsenic trioxide
dissolved in ammonia. It gives high degree of protection and better
penetration due to the presence of ammonia, which swells in the bamboo
structure

CCA and CCB

Copper Chrome Arsenic (CCA): water-borne fixing type:
It is a heavy duty broad spectrum preservative patented as AsCu; the
formulation consists of arsenic pentoxide and copper sulphate with
sodium dichromate as the fixative in the ratio 1:3:4. CCA has been found
to provide protection for 50 years or more. Due to the arsenic component
only exterior applications are recommended. Though no study has
revealed adverse effects due to exposure to treated products, it must
nevertheless be handled with special care.

Copper Chrome Boron (CCB): water-borne fixing type:
It is a broad spectrum preservative containing boric acid, copper sulphate
and sodium dichromate in the ratio 1.5:3:4. It is a good alternative to
CCA but less effective with a lower degree of fixation, of the Boron
component.

Zin and Penta

Zinc Chloride/Copper Sulphate: water-borne non-fixing type: These
are single salts and offer limited protection. They are highly acidic and can
cause corrosion of metal fittings. Zinc Chloride is highly hygroscopic and
treated bamboo will give a wet look in rainy season. This can adversely
help paints and other finishes.

Sodium Penta Chloro Phenate (NaPCP): water-borne non-fixing
type: It is basically a fungicide. It is also applied with boric borax for
protection during shipment and storage of green bamboo. But due to its
toxic nature it has been banned in several countries. It is the most
effective chemical to prevent moulds and blue stain fungi.

Boron Preservatives

Boron containing compounds: water-borne non-fixing type:
These are usually a mixture of boric acid:borax. Readymade formulation
(disodium octaborate 1:1.4) is also available. Boron salts are effective
against borers, termites and fungi (except soft rot fungi). High
concentration salts have fire-retardant properties. They are not toxic and
can be used for treating bamboo products like baskets, dry containers, etc.
which come in contact with food products.

Different types

Water-soluble salts are dissolved in water. On treatment, the water
evaporates leaving the salts inside the bamboo. These are further
categorized into non-fixing and fixing types.

These are leachable solutions and their use is restricted to bamboo used in
dry conditions and under cover. Bamboo treated with these preservatives
should not be exposed to rain or ground contact. Common example:
Boric acid: Borax & copper sulphate

These formulations are proportionate mixtures of different salts which
interact with each other in the presence of bamboo/wood and become
chemically fixed. In principle, the degree of fixation and efficacy depends
upon the nature of the components and their combination. For example,
Chromium is responsible for fixation, copper is effective against decay
fungi and soft rot and the third compound acts against insect and fungus.
The process of fixation requires some weeks during which the material
should be stored under cover. Slow fixation is preferred in case of bamboo
as it allows diffusion and better distribution of preserving salts.
Common example: Copper-Chrome-Boron, Arsenic Pentoxide & Boric
Acid

Coal tar and creosote available from coal is a dark brown viscous liquid.
Creosote should be used exclusively for pressure processes or hot and cold
treatment. Being oily, it imparts water repellence to the treated material. It
is effective against fungal and insect attack. Due to its dark brown colour
and bad odour, its use is restricted to exterior applications, especially in
contact with mud/ ground

These are slightly more expensive preservatives where the organic solvent
acts as a carrier for toxic molecules and later evaporates, leaving the active
ingredients behind. They are available commercially in ready-to-use
forms. A good formulation is an appropriate mixture of fungicides and
insecticides. There is little change of colour of the treated material but a
residual odour may remain for some time. The method of use will be
recommended by the manufacturer. Formulations available in
concentrates are more economical to use.
Common examples: Trichlorophenol (TCP) and Copper/Zinc
napthenates (metallic soaps) are used as fungicides. Lindane/
cypermethrin is used as an insecticide.

Some naturally occurring materials can prevent decay to some extent.
Long-term protection is not possible through these preservatives.
The Giant Indian Milkweed is deadly to beetles and fungi. Boiling of slivers
with fresh leaves and stem of this plant for 30-60 minutes will prevent
attack.

Types Of wood Preservatives

Water-Borne Types

Non-Fixing type preservatives

Fixing Type preservatives

Oily Preservatives: Creosote

Light Organic Solvent-based Preservatives (LOSP)

Natural Toxicants

What is wood preservation

The term wood preservatives defines that the wood preservation is the process of preserving wood from the wood destroying agents like insects or fungus so that the life span of the wood can be extended. It refers to the treatment of wood with chemicals to impart resistance to degradation and deterioration by living organisms. The proper application of chemical preservatives can protect wood from decay, and stain fungi, insects and marine borers, thus prolonging the service life of woods for many years.

The wood contents celluloses, hemicelluloses, starches and other susceptible materials that attract the fungi and insects to be degraded and eaten. After the preservative treatments, the fungi and insects cannot decompose and feed on these substances, hence the durability of wood is to be increased.

Wood Preservation

Hi Everybody,

welcome to wood preservtion blog.

lets save wood. Lets save earth.

Lets start a movement to save wood. This is my very small but honest try to save wood.

Anybody can join. Love wood. Join me to give better future to our children.

Shrikrishna Kulkarni