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Pressure Treated Wood And Gardening

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,

John Bumby
The Maine Wood Treaters

Thanks for your insight John.


  1. seedling said...

    Thanks for the info. We recently put in a raised vegetable bed and had inadvertently used pressure-treated wood. Upon learning more, we opted to pull it out and replace it with untreated pine. I'm glad we did just the same. But it's good to know positive steps are being taken by the industry.
    Ki said...
    I always wondered about the toxicity of pressure treated lumber. I purposely used untreated wood to create low raised beds for veggies but they rotted quite quickly. Just as well since the rabbits, deer, ground hog pretty much decimate the crop anyway so I don't plant a vegetable garden anymore. But interesting information nontheless if I revive my interest in growing veggies again though I would still be leery of using anything with copper in the garden. I believe copper is implicated in Alzheimer's which my poor mother has. It's a terrible disease and I self monitor regularly - any slip of the memory causes me a great amount of consternation.
    Anthony said...
    Seedling, yes, that was a good move to replace that wood. Better safe than sorry.

    Ki, sorry to hear about your mother's condition. You have my sympathies.

    I also have a question for you. What about copper plumbing? I'll have to research this, thanks for bringing it up.
    Ki said...
    Hi Anthony, I believe copper plumbing is implicated as a cause of Alzheimers. I don't know how much of a cause it is but better to err on the side of caution imo.

    My wife's mother also has senile dementia which a neurologist friend claims is the same as Alz. So we have always used a water filter. But I was curious if it removed dissolved minerals as I thought copper would be classified as such. Called the filter company but they were very evasive about this which made me uneasy. We drink bottled spring water now but who knows if that's not any better than our tap water. It has to be piped through some kind of tubing which would probably be copper?
    Anonymous said...
    So I forgot my password, but this is JohnnyB from The Maine Wood Treaters again. Thank you for reposting the information I provided about raised garden beds and pressure treated.

    Let me also reply to the comments about copper. Yes, there are links between copper and Alzheimer's in labs. There are also studies that copper can help Alzheimer patients. Go figure. Here is a good website explaining copper: http://www.bigy.com/content/haba_health/nutr/nutr_copper.php

    Let me also add that copper is used as piping for drinking water, cookware, coins like the old penny and the nickel, and even as an IUD for contraceptive uses. It is also used in MicroPro, a treated wood product that received an EPP status from SCS (Scientific Certification Systems). EPP means Environmentally Preferable Product. A complete 180 degree turn for this type of product in this industry.

    In regards to copper being released from this product. When a solid particle of copper is forced into the pores of the wood under an extreme amount of pressure, it stays there. Over time, small cracks and fissures can form in the wood, dropping an extremely small amount of copper out. Where does this copper go? This copper actually renders itself biologically inactive, therefore, eliminating any eco-toxic impacts. Basically, you'd see this as adding a mineral to the soil – copper in its naked form – and nothing to worry about. You add minerals all the time, even when organic gardening.

    Let me also explain the language. When you read an end tag, which is your warranty, you will see a use category. These will typically be above ground contact and ground contact. Also, there will be a place on the tag, perhaps the back side, which will say a number followed by this: PCF. This is “pounds per cubic foot” of chemical in the wood. This is a small number, like .08 for above ground. Think about that, .08 pounds per cubic foot. And think about what a cubic foot is: 12” x 12” x 12”. There is such a small amount of copper in this wood, and a fraction of that will fall out over time, and that fraction that does fall out is as solid copper one would find as a mineral anyways, so where is the concern?

    Let me touch upon another reader's comment, reading that it should not be used where the preservative may become a component of food, animal feed, or beehives. What this is talking about is that you don't want to use it to build a place where you plan on your honey bees living – bees are considered a pest to the treated industry, and so the wood is designed to combat them. You wouldn't want to use treated wood as a feed trough for pigs because they could chew on it. It is basically saying use common sense as to where you place this. It is one thing the one part per million copper escaping the wood into the ground, it is another to have a pig crunch on it for dessert.

    I readily admit that I am as skeptical as the next person. I buy organic and natural, but over that, prefer to buy local or grow it myself. This is how I cast my vote monetarily, so to say. One thing that every one of you has to remember is that extreme in any direction is not good. Sure, you can use pine to build your beds and replace them every other year, which puts a strain on many things as well. Think about this. My product lasts 40 years in the ground. Pine lasts two years. Wood is renewable and the original green product, if managed correctly. If every person out there used pine instead of PT, what would happen? You are using 20 times the amount of wood. How much extra fuel would that burn, go into the atmosphere, and water your organic plants with? What other impacts does that have?

    Going “green” isn't necessarily buying that expensive solar panel for $26,000. So you are now saving $50 a month on electricity, and you will get a return on that investment in 43 years. Well done. You could spend less and save more re-insulating your house and protecting it against heat loss by combating the three types of heat loss: radiation, conduction and convection. Now you have cut your heating and cooling expenses in half. Which is more green? Which truly saves more? Don't misunderstand me, solar has its place, but using a little common sense should have its place too.

    If you have more questions, some of you have found me. Well done. Here is my email address if it is allowed. I will make myself available to answer questions or comments. I am not interested in arguing with anyone, however. If you believe something is bad and you want to argue with me that it is bad, I am not going to change your mind, and therefore, refuse to argue with you. The information is out there and only you can change your own mind. Here is my information: jbumby@mainewoodtreaters.com. Contact me if you have questions you want answered or advice you would like to ask. I am human and make mistakes. I can only give you the best information I have. Thank you,

    Anonymous said...
    Oh, and one last thing while I have the floor. (And if this creates its own post, this is regarding pressure treated wood in the industry). Some of you have been burned by pressure treated lumber rotting out too quickly for your landscape timber needs. Yes, you may have gone to a place and the wood was much cheaper than any other place around, noticed it was PT, and figured you got one heck of a deal. Because this scenario always happens, right?

    I said before that the tag has the warranty information on it. If you got something approved for ground contact, then it probably isn't the above scenario. You most likely purchased "non-spec" or "treated to refusal". Both represent the same thing, an under treated product. This is a black eye on the industry. It rots, not as fast as the same species would untreated, but much quicker than what you want all the same.

    I receive constant calls about this. It is frustrating. We are in this business to make wood last longer, period. This product does not fall into this category. When I hear the frustration in someones voice after they spent the money --- AND MORE SPECIFICALLY, THE TIME --- to install this stuff to have it rot in 3 years, it is very sad. Please think about how important your time truly is. Sure, you can save a couple bucks by using this stuff. But when you need to rip it down to reinstall or install something different because it failed, you will have spent more money and have invested at least three times the original amount of time had you used the correct stuff.

    The worst part is, no one tells you. You need to research this yourself. If there is no tag, don't use it. If the tag doesn't say it is approved for ground contact, don't use it in the ground. Period. You are not saving money and may come to distrust of all pressure treated products. And I certainly do not want that.

    Thank you,

    The Maine Wood Treaters

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