What is treated lumber treated with, anyway?

I helped a friend build a home in New Orleans back in 2011-2012 and because of the location, we did two things:

1. Sink pilings into the earth on which to build a raised (pier) foundation

2. Apply pesticide to the top of the pilings to make them last as long as possible. I was warned not to touch the treated pilings with bare hands because the treatment liquid was toxic. 

At any given day in the area of New Orleans, there is a pile driver somewhere driving pilings into the unstable earth. This is evidenced by the thunk, thunk, thunk sounds off in the distance.  And any given day, termites and water rot are eating away at precious wood homes if they get past the pesticide or water barriers.  These enemies are mostly silent and almost undetectable until major damage is done.   

So what chemicals are used to treat residential wood against insects and rot?   Are they toxic?  A good video to watch on this subject talks about the history of treated lumber used for residences and parks.  Here’s what they found out:

• Up until the early 2000’s, wood was treated with something truly toxic: Chromated Copper Arsenate, or CCA.  CCA was the main chemical used to treat lumber for residential construction.  Arsenic can be very poisonous, and considering that decks, playgrounds and park benches are touched frequently, the EPA decided that any arsenic in the wood was cause for concern.  In January 2004 the EPA banned the use of arsenic-based CCA in residential market, but allowed it in commercial and industrial markets.  It’s important to use gloves and a facemask when cutting wood that may have been treated with CCA.

• Two new treatments were developed to replace CCA:

• Alkaline Copper Quaternary (ACQ)

• Copper Azole (CA-B).  Some companies like ProWood use Micronized Copper Azole (MCA), which contains copper and tebuconazole (What Chemicals Are Used in Pressure-Treated Lumber?)

The problem with the two new treatments is that although the EPA said they were not toxic to humans, they were not as effective against rot and pests.  If the lumber companies increased the amount of copper in the wood (from about 20% to 95%), the treatment was effective, but this made the lumber super-pricey.  Therefore they divided the market into 2 categories: ground contact and non-ground contact.  Ground contact was for posts that are surrounded by damp soil all day and correspondingly had higher levels of ACQ and CA-B, while non-ground contact wood, with less treatment, is meant to be used for decking and handrails, as well as framing lumber.  The lumber sticker on the end of the boards will tell you which is which, if you’re unsure.

But are they really not toxic to us?  The “quaternary” should ring a bell… many handsoaps contain quats and we’ve written about them in this article.  Quats kill microbes by binding to the negatively-charged surfaces of microbes.  They have been studied to induce asthma in cleaning workers, decreased lung function in farmers, and greater immune reactions and decreased fertility in mice, among other effects. They are very persistent and are difficult to remove from surfaces, so it’s important not to use them on food prep surfaces.  Most risk of contact with these products would be to carpenters and workers who cut and handle it frequently.   Copper is also toxic to marine life. 

Today wood is “pressure-treated” meaning that it is forced into the wood with extreme pressure.  This video explains all the steps of pressure treatment, but here are some of the important ones:

• Relatively dry wood (as measured by industrial moisture meters) is loaded into a horizontal, cylindrical tank, which is then sealed closed.

• A vacuum pump removes all the air from the tank, as well as air from the wood.

• The tank is flooded with the treatment solution.

• The tank is pressurized to about 140-150 pounds per square inch to force the solution deep into the wood.

• The tank is depressurized and the unabsorbed treatment solution is pumped back to a tank to be reused with the next batch of wood.

Despite this high pressure, the treatment solution cannot penetrate wood all the way through, unless it’s a thinner variety (like “one by” such as 1x6 feet, 1x 8 feet, etc.)  This thickness measurement, although it says 1”, is actually only three-quarters inch thick.  Therefore, when cutting bigger pieces of lumber like 2x or greater, the cut ends will expose some untreated wood in the center.  Therefore, carpenters commonly paint a wood preserver or sealant on the cut ends to protect the cut end.  These treatments in themselves can be toxic.  Some are oil-based and some water-based. 

If you are using treated lumber as a deck or playground or picnic table where people will touch it everyday, there are safer alternatives, but you also have to consider how they are produced:

• Some types of wood, like cedar, cypress and exotic woods like teak are naturally pest- and rot- resistant and don’t typically require additional pre-treatment, but can cost a lot more and still need some maintenance.  This is the most natural route. 

• Modern Mill is a company that upcycles rice hulls into synthetic wood in various sizes and shapes.   It claims to be water, weather and pest resistant, it won’t rot or splinter, is non-toxic and formaldehyde-free, and looks like real wood.  Fifty percent of the final product is rice hulls, blended with close to 20 other ingredients (undisclosed), and waste product from milling is re-ground and fed back into the production of new product to minimize waste.

• Other composite wood companies like Azek, FiberOn and TimberTech make unique products that have their own advantages and disadvantages.  With these, as with Modern Mill, upfront cost is more but maintenance is less and your project tends to last longer.  Composite wood is a mixture of wood fiber, recycled plastics and “binders” or glue to hold it all together.  All of the “recipes” for specific ingredients and chemicals are proprietary, though, so we don’t know what exactly goes into the products (or what is off-gassed from them).

• HDPE lumber (plastic lumber) is made from the same material as milk jugs and some brands are even made completely from recycled plastics.  HDPE lumber claims to be more durable than composite, because composite still contains the organic wood component, which is susceptible to water and pests.  It’s also highly resistant to UV rays and extreme weather conditions, making it longer-lasting. (What is Composite Decking?)  Most organizations consider HDPE to be non-toxic.

Decks and additions to your home are expensive projects, and along with considering the potential toxicity of the material you use, you’ll want to calculate the trade-offs among upfront cost, maintenance and longevity.  We didn’t even mention that you could go with something non-wood and non-plastic altogether: when replacing an old lake dock on my property, I decided to repurpose some aluminum decking panels that a contractor had salvaged from a stadium he was renovating.  I also used metal “auger feet” attached to metal fence piping to replace the pilings (it’s a light-duty dock), so that there was little disturbance of the lake bottom as I screwed them in.  The dock surface is hotter to the touch during the summer, but there’s no chemical treatments that will leach into the lake or our feet, I will never have to replace anything on it (well, maybe some screws and bolts if they rust out), and splinters are not a problem.  Every project deserves a good amount of brainstorming and planning to come up with the best, healthiest solutions long-term!

Photo by Roberto Sorin on Unsplash