You Wood Never Believe This

Last week I gave my 17-year-old daughter the speech about how when something looks too good to be true, it usually is. A teenager’s life is certainly challenging and doesn’t need to be complicated by Internet scams, Lance Armstrong-type role models, and cyber-boyfriends who don’t really exist. This made me think about a building material that has proven to defy this principle.

I have been in the wood window business for 26 years and have been very dismayed at the poor quality of manufactured windows in the United States. As a result, my company is constantly searching for better finishes, exterior cladding methods, preservative treatments, and more durable wood species. It was in this quest that we ran across a wood called Accoya. The website said the wood is guaranteed to last 50 years unfinished above ground and is more durable than teak. Normally I would have just laughed and then placed another order for mahogany, but the fact that the product has been used in Europe for the past 75 years piqued my interest.

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Accoya is radiata pine that is subjected to a proprietary non-toxic process that permanently changes the molecular structure of the wood. Accoya is based on acetylated wood technology which is a process that impregnates wood with acetic anhydride, which is similar to a very strong vinegar. This produces a wood that smells like the salad I had last weekend. The process involves placing the lumber into massive pressure vessels and forcing acetic anhydride under immense pressure into the very core of the wood. This process is then reversed and a vacuum removes 99.7% of the liquid from the wood, leaving the radiata pine permanently altered. The resulting product is a wood that absorbs water, but doesn’t swell up in the process so its dimensionally stable, impregnable to fungi, and not attractive to insects. Sounds too good to be true, doesn’t it?

The engineers at Re-View put the product through our own testing regimen to see if we might consider it for window fabrication. We took sample wood blocks of Accoya and tested the internal moisture content and measured the outside dimensions with a micrometer. We then submersed the wood blocks into a bucket of water for 30 days. When we removed the blocks and tested the moisture and dimensions, nothing had changed. That single test convinced our team that this wood had serious potential.

Our next step was to see how the wood reacted to all of the other products that come into contact with the wood. Of primary importance was how different finishes reacted to the acetylated wood. Sherwin Williams conducted a series of tests and determined that the best combination of exterior finishes was an oil-based primer with an acrylic latex intermediate and final finish. The wood was exposed to 1540 hours of testing in a humidity chamber and freeze/thaw cycles from -5F to 120F. The finishes passed with flying colors. One thing we did discover is that the wide grain pattern of the radiata pine is not very suitable for an interior stain application. Accoya has recently made improvements by introducing an acetylated alder option that stains much better than the radiata.