Micronized Copper Azole (MCA) is a preservative used in the pressure treatment of residential application wood products. Micronized copper azole can be used above ground, in ground contact or in freshwater contact. The benefit of wood treated with MCA and micronized tebuconazole is long-term protection of wood and its reduced toxicity compared to earlier pressure-treated wood varieties, allowing it to be used for residential projects.
Pressure Treated Wood Before MCA
Prior to 2004, pressure-treated wood for residential use was preserved with chromate copper arsenate (CCA). When concerns arose about the toxicity of arsenic in CCA, alternative preservatives were developed. MCA is one of the many different copper-based wood preservatives available. It contains higher levels of copper than CCA, which makes wood treated with MCA more expensive. To offset those costs, manufacturers now produce pressure-treated lumber with different copper retention levels. CCA-treated wood is still produced for certain institutional, industrial and agricultural uses; however, it cannot be used in residential applications.
Understanding Retention Levels
Retention level refers to how much of the preservative is retained in the wood after the pressure treatment is complete. Retention level is expressed in pounds per cubic foot (lb. per cu. ft.) of wood fiber. The higher the retention level, the more effectively the wood will ward off decay caused by insects and moisture. Wood with a higher retention level has more copper and, therefore, is more expensive.
In order to get to the required retention level, some species of lumber (such as Douglas fir, hem-fir and spruce-pine-fir) have to be incised, which allows the preservative to penetrate the wood more deeply and uniformly. Tests conducted by Forest Product Laboratory have found that this practice results in a reduction of bending strength and stiffness. For this reason, incising is more common with timbers and more substantial boards.
Categories of Residential Preservatives
Listed below are the categories of residential preservatives:
Copper Azole (CA)
The most common wood preservatives used for treating wood intended for residential building projects fall into two formulations of copper azole (CA-B and CA-C). The American Wood Protection Association has established minimum retention levels for wood treated with these preservatives. A board treated with CA will indicate the retention level on the label.
The CA preservatives are copper-based and include organic co-biocides instead of the toxic chromium and arsenic used in previous models. The copper in the chemical used to pressure treat the wood is dissolved chemically in an organic solvent. The copper formulations cause the wood to have a green cast. It is clean, paintable and well-protected from insects and rot. However, CA-treated woods are very corrosive to metal. As a result, only ceramic-coated, stainless steel or other approved fasteners should be used on this kind of treated wood.
MCA
The second category of preservatives includes wood treated with variations of CA. The preservatives are known as micronized copper azole (MCA). The copper in MCA is ground into microscopic particles. The tiny particle size eliminates the need for solvents to dissolve the copper into the water-based treatment solution.
The chemistry of MCA impregnation is also different from typical wood preservative treatments. In MCA-treated wood, the copper is present in microscopic particles suspended in water and injected into the wood. Part of the copper azole immediately solubilizes during the treatment of the wood and is complexed by wood organic macromolecules, while another portion of it does not react to the wood. Instead, it provides a reservoir and the remaining copper azole particles are solubilized later. This slow process helps to provide continuous protection against decay caused by fungi and mold.
Advantages to Using MCA Treated Wood
MCA-treated wood offer advantages over wood treated with CA. One of the most important advantages is that the copper in MCA-treated wood is less corrosive to fasteners and hardware than the copper in wood treated with CA. Additionally, MCA-treated wood can come into contact with aluminum without discoloration or corrosion. Another advantage is that wood treated with MCA keeps more of its natural color. The lighter color will have a more pleasing appearance, and it can be painted with light-colored paints or stains.
MCA-treated wood is less prone to off-gassing as well. The microparticles are forced into the wood under pressure with no solvent. This process ensures that the preservative will hold up to the exterior environmental factors much better than other types of treated wood.
Projects Suitable for MCA Treated Wood
MCA-treated wood is a good choice for any residential or commercial application in which the wood will be exposed to outdoor elements. It can also be used in applications such as decks and fresh water docks.
Contact the Lumber Experts at Curtis Lumber and Plywood for More Information
To make sure you get the right pressure-treated wood for your project, contact Curtis Lumber and Plywood. The lumber experts at Curtis Lumber and Plywood are available to help you pick the right type of wood for your specific project and provide you a variety of wholesale options to choose from. Contact them for information and to arrange a delivery.
