Woods like cedar, cypress and redwood weather attractively, and even pressure-treated lumber acquires a natural gray hue after a few years. But most other woods require some sort of protection from rain and sunlight.
If you want to protect your wood projects or simply dress up pressure-treated green, you can do the job with a good stain.
Oil-based set the standard (and was the only option till recently), but latex technology has made it possible to use water-based stain outdoors. While oil-based is still said to bond better to new wood, latex has three main advantages: easier cleanup, less environmental harm, and it holds its color better for longer.
On vertical surfaces, you can use a couple coats of either solid or semi-transparent stain. Your main consideration here is looks. A solid stain covers the wood completely, like paint, while semi-transparent lets the grain show through. The color of the wood affects the semi’s color, so you might do a couple tests before making your final choice.
On decks there’s no contest; use semi-transparent. A summer’s worth of barbecue parties will have most solids (which tend to sit on top of the wood), peeling. A semi bonds better without surface buildup, and shows wear and tear less. While you’ll still have to recoat it after two or three years, it’s an easy job; no scraping and sanding.
Proper prep: To season your wood, some experts suggest waiting a month; others say wait till spring to stain an August-built deck. The key is dry wood: no more than 11 percent moisture content. (Of course, it’s best to start with good kiln-dried lumber.)
Before staining, wash with trisodium phosphate (TSP), rinse well, and let it dry for a few sunny days.