3 Common Types of Pressure-Treated Lumber

Wood Trim
Pressure treated lumber consists of wood that contains chemical substances meant to deter pests and prevent wood rot, thus extending the lifespan of the lumber. Once upon a time, all such wood was treated with a substance known as chromated copper arsenate, or CCA. But in 2004, health and environmental concerns forced manufacturers to stop producing such wood.
Since then, a variety of different pressure treating methods have arisen, with each utilizing a different chemical treatment. Even within the contracting and building industries, many people still fail to understand the distinction between these methods. This article will help you get your facts straight by discussing three of the most common varieties of pressure treated wood on the market today.
1 - ACQ
The chief problems that eventually forced CCA off the market involved its heavy reliance on the use of the chemicals chromium and arsenic. These highly toxic substances pose serious environmental concerns when it comes to the disposal of old lumber. Ammoniacal copper quat, or ACQ for short, represented one of the first replacement options to CCA.
ACQ effectively replaces chromium and arsenic with a much higher concentration of copper. This ensures an equally effective preservation of the wood as time goes on. Copper acts to destroy a wide range of microorganisms that lead to wood degradation - yet it won't destroy all of them.
For that reason, ACQ also contains a co-biocide known as the quaternary compound. The quaternary compound ensures protection against things like insects and fungi whose activities copper alone cannot restrict.
2 - CA
ACQ pressure treated lumber has a close relative that goes by the name of copper azole or CA lumber. Like ACQ, CA involves the use of high concentrations of copper. Both forms incorporate this copper in its ionic form - a method that allows you to easily disperse the copper in a solvent solution, which is then forced into the wood grains by means of high pressure.
ACQ and VA differ with regard to the co-biocide used. CA eschews quaternary compound in favor of azole. The similarities between the two tend to be much greater than the differences. The key thing to realize about both ACQ and CA is that their high copper levels make them especially chemically active.
Herein lies the greatest drawback of both ACQ and CA: their elevated potential to cause corrosion in metal fasteners. Copper exerts a highly corrosive effect on both steel and aluminum, meaning that screws and nails made from such substances stand a greater and greater chance of succumbing to rust and corrosion as time goes on.
3 - MCA
The solvents used to disperse the copper ions in ACQ and CA act to increase their corrosiveness many times over. For that reason, manufacturers turn to alternative methods of dispersing the copper. Micronized copper azole, or MCA for short, represents a significant breakthrough. Here the use of a solvent can be eliminated by breaking the copper particles up into tiny sizes.
The copper particles used in MCA measure as little as one-millionth of a meter in size. The lack of solvent, as well as the fact that the copper does not have to be in an ionized form, means that you can keep corrosion at bay. This allows contractors to use aluminum and steel hardware without worry.
MCA offers a secondary benefit in that the smaller copper particles stand less of a chance of being leached out of the wood over time. This allows the wood to retain its protection well into the future. It also reduces levels of bioaccumulation, thereby posing less of a risk to organisms in the immediate environment.
Lumber Experts
Choosing the right lumber for a building project can be a daunting task. Those who want to ensure the best results should always consult with a wood professional before making their final decision. If you would like to learn more about pressure treated wood, please don't hesitate to contact the industry experts at Larsen Lumber.