“Treated” lumber…. also known as pressure treated lumber… is an essential building component for outdoor structures. By pressure treatment, it’s meant that chemical preservatives are forced under pressure deep into the cellular structure of the wood, which helps the wood maintain a barrier against insects and decay for a long period of time. It’s available as boards or posts or even plywood, and is used in residential projects for landscaping, decks, fence posts, swing sets, mailboxes etc.
Historically there have been 3 main types of wood preservatives: water-borne, oil borne and creosote. Of these, the newer and less-toxic water borne (copper-azole based) chemicals are used primarily in pressure treated wood products for residential use. Though the industry claims that pressure treated wood from water-borne chemicals are safe for human health, those wood products still carry warnings on acceptable uses (do not burn or inhale toxic fumes etc).
Once the lumber has been pressure treated, it will increase greatly in moisture content from the infusion. Thus, there can be a large amount of initial shrinkage in the lumber for awhile. Most suppliers recommend that you seal your new treated lumber at first, then wait to paint it until shrinkage has occurred so the paint will adhere. This link also gives you the levels of preservative retention for various uses of treated lumber….. check out their chart below to make sure that you’re buying the right product for your own use (garden, deck, whatever). The number will be stamped or attached to each piece of lumber to identify it.
POTENTIAL ISSUES WITH PRESSURE TREATED LUMBER: “Cupping’ is a term that refers to the bend of the wood across its width as it dries. The sun can cause cupping (faster drying) so ideally boards could be installed with the rounded side up, or in some other configuration to protect from direct sun shrinkage. Some lumber mills re-dry the lumber and pressure treat it a second time…. making it less likely to twist, warp, or cup. And water resistent chemicals can be added as well. Installers need to be aware that there can be a corrosive quality of the wood towards some types of nails and brackets.
HERE’S an example of the various options available for purchasing treated wood timbers. And this link walks you through the ideal way to stain a pressure treated wood deck.
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