9 mighty woods for outdoor projects
Treated woods are common choices
Early in 2004, the old CCA (chromated copper arsenate) treatment that contained arsenic was replaced by various treatments, but the most common is ACQ (alkaline copper quat). In spite of its shortcomings, ACQ-treated wood holds up well. It might crack, warp, or shrink, but it won't rot or prove tasty to insects.
ACQ is a water-based preservative forced deep into the lumber, usually Southern yellow pine. Consequently, the lumber is saturated when banded and shipped. This practice makes treated wood heavy and prone to the troubles listed previously. To avoid these tendencies, you can air-dry treated lumber for two warm months, or purchase KDAT (kiln-dried-after-treatment) lumber. The downside: cost (usually double the wet stuff) and the need to special-order it from lumberyards or home centers beforehand.
Because the preservatives are accepted only by the sapwood, heartwood of pressure-treated lumber is not decay resistant, typically appearing tan or pink instead of green.
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