Toxic Chemicals in Untreated Framing Lumber

October 6, 2015, by Debra Lynn Dadd

This post started as a comment posted this week on Q&A: Is Fresh Cut Lumber Toxic?

My wife and I have done a fair amount of home improvement over the years and we have purchased our share of lumber from big box stores but have also supported a local sawmill buy purchasing wood from them. The wood we purchase directly from the sawmill does not have the chemical smell we always notice when we buy from a big box store (or even a lumber yard).

Lately we have been wondering if big lumber producers try to cut down on the time lumber spends drying in the kiln by applying some undisclosed chemical to prevent mold. Are they required to disclose every chemical they might apply to their wood products?

But I pulled this comment out and made it a question because the answer turned out to be so important.

I’ve purchased a lot of framing lumber at places like Home Depot and Lowe’s. I’ve not purchased lumber at a local sawmill, so I didn’t have anything to compare it to. I myself didn’t notice an odor and I didn’t have any symptoms. And of course there is no label, so you think it’s 100% untreated wood.

But once I received this comment, I starting researching and here’s what I found.

There’s an answer to a question on the website The Chimney Sweep (of all unexpected places) that exactly answers the question of chemicals in framing wood. It’s in the context of what happens to a wood stove when you burn framing wood, which chimney sweeps would know.

The trip through the sawmill can also introduce chemicals to the wood. To combat "blade binding" and keep the sawblades sharp, sawmill operators must constantly keep the blades coated with liquid lubricant, using a sporadic spray-on or continuous drip method to keep the sawblade coated while the wood is being cut. A variety of chemicals are commonly used as sawblade lubricant, including diesel oil, antifreeze, paint thinner and kerosene. Trace amounts of these chemicals can be found on all surfaces of each piece of lumber that has been through the saw. Combustion of these substances produces a variety of corrosives, including sulphuric acid.

Another chemical that finds its way into dimensional lumber is polyethylene glycol (PEG-1000). In recent years, a process known as "dry kilning" has become the industry standard for drying lumber, as it enables much faster removal of the natural liquids contained in the tree. Dry kilning allows much more efficient processing of dimensional lumber, but it can cause excessive shrinkage and cracking of the wood: to prevent this, the green logs are soaked in a solution of PEG-1000, which infiltrates deep into the wood fiber and "bulks" the wood so it won't shrink or crack in the kilns. PEG-1000 is sometimes used even in old-fashioned mills where dry kilning hasn't yet been implemented, because after kilning, trace amounts of PEG-1000 migrate to the surface of the lumber, creating a "waxy" coating on each piece which inhibits oxidation and natural enzyme breakdown of the wood fiber. This waxy coating actually provided one of our first tip-offs to the emerging use of PEG-1000 several years ago, when a long-time employee at our local lumber yard complained that he had recently learned he must be extra-careful moving stacks of lumber with his forklift, because if he stopped too suddenly, the then-new "slippery" lumber would slide right off the forks. Thermal decomposition of PEG-1000 produces aldehydes in extreme concentrations, which combine with the natural aldehydes and water found in wood exhaust to create a corrosive acid bath inside the stove, stovepipe and chimney.

For various reasons, including the waxy surface situation, furniture-grade lumber is not typically soaked in PEG-1000. But that doesn't mean the leftovers from your local cabinet shop are chemical-free. Once out of the kiln, lumber is stacked in bunches separated by wood slats called "stickers". Over time, these stickers can cause discoloration of the wood, resulting in off-color stripes across the grain known in the industry as "sticker stain". Affected lumber is sometimes treated with "wood wash", a solution of oxalic acid, which bleaches out the stains. In weak solution, oxalic acid is commercially used as a rust-remover: at temperatures above 110° F, the corrosiveness of this organic acid triples.

Another source of chemical content in dimensional lumber is the use of fungicides. Prior to storage of green lumber, especially in wet or humid locales, chemicals may be applied to prevent growth of fungi which stain wood blue or black, a phenomenon known as "sapstain." Fungicides may be applied in the production line (usually by spraying) or after the lumber is bundled (usually in dip tanks). Chemicals used include didecyldimethyl ammonium chloride, 3-iodo-2-propynyl butyl carbamate, azaconazole, borax and 2-(thiocyanomethylthio) benzthiazole.

It should be reiterated here that the above list includes chemicals that might be found in untreated dimensional lumber. For example, most inland mills don't start with logs that have had a saltwater bath: many mills have not yet adopted the "dry kilning" method, and don't soak their logs with PEG-1000: not all furniture-grade lumber has been treated with oxalic acid, and not all mills dip their lumber in fungicides. The problem is, you can't tell if a truckload of mill ends contains any of these chemicals by looking at it, and the woodseller who's delivering it isn't likely to know either.

A woman recently called me for a consolation and told me she was building a log cabin out of logs from the local forest that were being felled and cut into logs by one person. Nothing added. That would be the way to get actual untreated lumber.

We apparently need the same kind of paper trail that exists for certified organic food with wood products in order to even locate toxic free lumber.

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