I received a really interesting comment the other day on an old post about building raised garden beds. The commenter works in the pressure treated wood industry and really provided a great explanation of the types of wood that are available and what's in store for pressure treated wood in the future.
Here's his comment in full. I feel that it deserves a new post instead of just remaining buried with that old post.
To add to the pressure treated question.
Pressure treated is my family business, and I would like to offer a fair opinion backed with research and personal experience. I am a fourth generation wood preserver.
For many years, the choice of pressure treated lumber was wood treated with CCA, Chromated Copper Arsenate. However, CCA has become a thing of the past except for in certain specific commercial and industrial markets. Let me assure you, it would not be easy for the average consumer to get their hands on it since the voluntary transition to newer, and safer chemicals.
Which brought us ACQ and Copper Azole. ACQ stands for Alkaline Copper Quaternary. The Alkaline holds the copper in a liquid form, and the quaternary is basically an anti-bacterial soap. Much better in many ways. However, as the author has pointed out, there is a flaw in this chemical. It corrodes aluminum as well as other metals. CCA and the other two choices have always recommended using stainless steel or other approved fasteners, however, the new guys on the block seem to have the predominant problem of corrosion.
Why does it really corrode? Copper doesn't get along with aluminum. Simple chemistry. The nature of this treatment allows a tiny amount of copper to leach out, which causes surface contact with any fastener. If that fastener happens to be aluminum, a chemical reaction occurs, and in a short time, maybe a couple years, no more fastener. But do not become discouraged. There is an even newer kid on the block.
You will see it as a few different names: MCQ, Smart Sense, MicroPro, MicroShades, or Micronized Copper Quaternary. ACQ is held in solution, a liquid. MCQ is chemically different. It is made of tiny (micro) particles of copper. These particles are forced into the wood cells or pores during the pressure cycle. Once in, they stay in, also forming a barrier keeping in the quaternary. The leaching of chemicals out of MCQ is practically non-existent. So much so that aluminum is actually approved for use on this type of treated wood.
It just started going into production the end of 2006, and is becoming available in almost all states. If you can not find it, request it, or shop somewhere they do carry it. Most of the independent lumber yards will carry it, and Home Depot has it available in some stores as well.
To add a side note, I purchase organic and/or natural produce when available. I did not want to use ACQ in my organic raised bed garden, if I had to, I would have use a liner. However, I am building raised beds this year, and dragging my feet paid off this time, because MCQ became available, and I trust the research behind this product. ACQ was the step away from CCA, MCQ is the step up to a new level of safer treated products. I hope this helps answer any questions. Thank you,
The Maine Wood Treaters
Thanks for your insight John.