How to protect wood from rain and weather wood preservatives

Protecting wood outdoors

Except for rot-resistant wood, such as redwood or cedar, raw wood exposed to moisture must be treated with preservative. Avoid highly toxic creosote and penta (pentachlorophenol) preservatives. Select a safer preparation with copper or zinc naphthenate, copper-8-quinolinolate, TBTO (tributyltin oxide), or polyphase. On shingles and siding, apply it liberally, using a natural-bristle brush or a pad applicator. Even these preservatives are hazardous as liquids. Wear a respirator mask, goggles, gloves, and long sleeves.

Whenever possible, dip wood in preservative-for at least 10 minutes. Put a picnic table’s legs in a bucket. Soak lumber in a box or trench lined with plastic; use a bulb-operated hand pump to suck leftover liquid back into the can. All low-toxicity preservatives require reapplication every 3 to 5 years. Only copper naphthenate can withstand ground contact.

Pressure-treated lumber

For hard-to-reach spots and for a major project, such as a fence or deck, buy lumber pressure treated at the mill with a long-lasting inorganic arsenical preservative, such as chromated copper arsenate (CCA). Pieces touching soil should be stamped LP-22; others, LP-2. Buy only dry lumber with no surface residue. Don’t use it where it will come in contact with food or drinking water. Seal a surface with a polyurethane varnish if young children will use it. Wear a mask to avoid inhaling or swallowing sawdust. Put scraps in the trash pickup; don’t burn them. Cutting exposes untreated areas; arsenical preservative is sold solely for coating cut ends.