For some western wood species, the treatment process differs due to incising needed for preservative penetration. See the short, animated video below on the treating process that includes incising.
Pressure treatment is a process that forces wood preservatives or fire-retardants into the wo od. These processes are considered the best and most effective method to extend and preserve timber life. Preservatives protect the wood from attack by wood ingesting insects; like termites, and wood rot caused by fungal decay. Fire-retardant tr eatments help the wood to quickly char when exposed to flame, reducing the smoke and flame that occurs in a fire.
Treated wood use applications include interior framing, exposed exterior wood for above ground or ground contact uses, fresh-water and salt-water exposures, and fire retardants for wall, roof and floor assemblies. Additionally, the pressure treatment process is used to protect utility poles, railroad ties, structural framing, fence pickets, deck boards, and posts.
Pressure treating wood provides deep penetration and retention of preservatives for uniform protection for wood products, ensuring the treatment formulation meets the appropriate wood standards and building code requirements. For some western wood species, incis in g is a common process where the wood is resistant to preservative penetration, but the preservative will penetrate along the grain.
These wood species are prepared by creating small incisions into the wood prior to the pressure treating process. Wood is an excellent renewable building material. However, when a wood product is used in contact with the ground or exposed to high moisture conditions it may be subjected to biological and insecticidal deterioration. As a result of termite or fungi attack, wood from most species can be destroyed within five to eight years. To extend the service life of wood to years in moist environmental conditions, it is important to use pressure treatment methods.
The objective of this fact sheet is to summarize the most commonly used pressure treatment methods, the basic principles, and some of the chemicals used for such processes. The purpose of wood pressure treatment is to force preservative chemicals deep into the cellular structure of the wood. The chemical acts as a barrier between the wood and biological deterioration agents, so that the service life of the wood can be substantially increased.
For most pressure treatment processes, moisture in wood is reduced before the application of the chemical. In the case of roundwood treatment, logs should be debarked using various equipment, such as rosserhead or ring debarkers. Incising is another process to prepare wood for treatment. Sharp steel teeth are pressed into the sides of timber or poles to increase the penetration of the chemical into the wood during the incising process as shown in Figures 1 and 2.
Table 1 also shows the effect of incising on the retention level of eastern spruce. In a typical pressure treatment process, wood is placed in a horizontal cylinder up to ft. The cylinder is flooded with the chemical followed by a cycle of pressure and vacuum. Pressure treatment methods are classified into two basics groups: full-cell and empty-cell processes.
In the full-cell method, both cell wall and lumen are filled with the chemical, while the objective of empty-cell process is to retain preservative in only the cell wall. The full-cell method is the oldest treatment process and was invented in by John Bethell. This method is generally used where a large amount of preservative is needed for certain applications such as treatment of utility poles, farm fence, bridge timbers, and pier timbers.
This process results in high retention, but not necessarily deeper penetration than that of other processes. In a typical full-cell treatment, the process begins with an initial vacuum to evacuate air from the cylinder. Later, the tank is filled with the preservative chemical and the pressure is increased to psi for several hours. Once the pressure time is completed, the preservative is drained from the tank, and then a vacuum is applied to clean the excessive chemical left on the surface of the timber.
The first essential step in the empty-cell method is the application of the initial pressure. As soon as the tank is sealed, an initial pressure of up to psi is applied to compress air into the cell lumens. Once the pressure treatment is complete, the lumber is moved to a drip pad until it cures and dries enough to be shipped to a supplier. The amount of time it takes to dry depends on the climate and exposure to sunlight.
A variety of treated lumber is available in a wide range of sizes and applications. Knowing the different types is important to making sure to select the right product for your project, saving you money and headaches later on. It can be used outdoors and indoors, and offers the workability of wood with the fire-safety benefits of non-combustible materials. KDAT prevents moisture-related problems— such as warping and twisting in lumber, or buckling or crowning in installed plywood projects—from occurring in the future.
Copper Azole CA Treated Lumber is pressure-treated with copper-based preservative that provides long-lasting resistance to decay, rot, and termites.
Chromated copper arsenate CCA is a water-based wood preservative that has been used since the mids and is instantly recognizable for the greenish tint it imparts to plywood. This preservative provides long-term resistance against decay, rot and termites. Questions have been raised about the safety of exposure to the CAA chemicals. Studies conducted by the Environmental Protection Agency have concluded that the chemical preservatives, most notably arsenic, have not been found to leach into soil or water.
Independent laboratory studies have also found no increased risk of cancer to those who work with CCA-treated wood on a daily basis.
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