Tips for Staining Decks and Other Exterior Surfaces in Washington DC and Northern Virginia
Wood is a strong and beautiful organic building material with one key weakness: being organic, it is vulnerable to organic decay. The properties of different kinds of wood are totally determined by the properties of the trees they were lumbered from. Some trees, like cedar and redwood, have their own innate resistance to bacteria, fungus, and insects, but many of the common softwoods used for decks do not. Pine, for example, which is a sturdy and easily lumbered variety of wood, lacks resistance. When raw pine is exposed to the elements in an exterior environment, it will fall prey to decay within a couple years.
One classic solution to wood’s vulnerability is to paint or stain the wooden exterior surfaces, so that the wood takes on the waterproofing and element-resistance of the chemical paint and stain. For the most vulnerable wood exteriors, however – like decks constructed from pine or douglas fir – providing surface protection is not sufficient to get long life out of a deck. Pressure treatment is a technique that has become popular because it offers a deeper level of protection.
Pressure-treating involves bathing the lumber in preservative chemicals, and then subjecting the wood to intense pressure, so that the preservatives become deeply infused into the wood. The most common chemicals used in pressure treatment are water-borne copper mixtures like chromate copper arsenate (that is the preservative that creates the familiar greenish tinge in exterior wood), alkaline copper quat, micronized copper quat, and copper azole. With pressure-treated wood, chemical resistance is borne deep into the pores, lending added protection to the wood’s interior.
However, just because the wood is pressure-treated, does not mean that it does not need to be stained as well. While the pressure treatment system is remarkably thorough, some spots will inevitably be missed, and the rot that sets in will slowly but steadily decrease the life of your deck. Staining pressure-treated wood can both extend the life and amplify the beauty of your exterior deck landscape.
The catch is, you can’t do it immediately. Because you can’t do it while the wood is still wet. Even when the wood is bought freshly from the store on a sunny day, if it is pressure-treated, you should assume that it is wet. This is because pressure treating by itself makes wood wet. The water that carries the preservative chemicals into the wood is driven in so deeply that it takes 30-60 days to dry fully – the exact drying time determined by the temperature and humidity.
Staining pressure-treated wood while it is still internally wet from the pressure-treatment process is one of the critical mistakes that leads to stain and paint failure on exterior surfaces. The moisture pushes out against the film or stain, forming bubbles in the coating, and the moisture locked into the wood encourages mold to grow, counteracting the very purpose of the preservatives and stain.
So the moral of the story: YES, go ahead and stain your pressure-treated deck (or fence!) – but wait 30-60 days first.