The lone voice of horticultural reason
Don’t use standard nails and fasteners with the new treated wood.
Out of the frying pan, into the fire. The EPA led the charge to ban CCA, the combination of chemicals used since the ‘70s to treat lumber for outdoor use. The ban went into effect last year, and wasn’t a bad thing—the “A” in CCA stands for arsenic, and while the University of Minnesota and other researchers concluded that the arsenic posed no public health risk, minute traces of arsenic were found to pass from the old treated wood into the environment, and, in rare cases, humans.
So now the new treated lumber is out on the market, made water- and rot-resistant with a combination of more environmentally friendly chemicals (ACQ – Ammoniacal Copper Quat, CA – Copper Azole). All appeared fine until the little pieces of paper noting grade and SKU number on the end of each board started falling off the lumber, before the lumber was ever shipped from the mills. The staples were frying off—in as little as 24 hours after being inserted.
Turns out the new treatment chemicals are corrosive. Impregnated in the wood, the lumber now fries up and eats metal. There are already reports of builders and homeowners watching their new decks fall apart as the nails, bolts, and stringer hangers used in the construction are quickly corroded to the point that they no longer hold the wood together.
If you buy lumber to build an outdoor structure—a deck, fence, flower box, timber retaining wall, etc.—don’t fasten the wood together using that old box of nails or bag of screws you have kicking around in the garage somewhere. Of course, if you choose to build a retaining wall (or edge a garden bed) with treated timbers, instead of stone, having the thing fall apart is probably what you deserve.
Instead, buy stainless steel or triple galvanized nails, screws, bolts, and hangers (standard galvanized gets eaten, too).
Build away, but keep your fingers crossed. Researchers are pretty sure they’ve solved the problem, but all they know for sure is that the new fasteners haven’t corroded in, well, about a year.
The Renegade Gardener