Even the best-built decks can't escape the assault of sun, water, and even insects. That's why the most important coat of finish your deck receives will be the first one.
For a new deck built with pressure-treated lumber, let the decking dry out for about two to four weeks, depending on weather conditions. Test the lumber for dryness by sprinkling water on the surface. If it soaks in readily, the surface is ready to receive a finish. Untreated lumber should be finished as soon as it is dry to the touch. If you wait too long, the surface of the wood will have begun to degrade already.
Penetrating finishes soak into the wood to help prevent it from water damage and more. Types of penetrating finish include the following:
- Water repellents are transparent, protecting the wood from water damage without altering its natural coloration.
- Water repellents with an added preservative combat mildew. Ultraviolet (UV) stabilizers are additives used in some clear finishes that offer some protection from sun damage.
- Semitransparent stains are more durable than water repellents. The pigments used in the stain protect better against sun damage.
- Penetrating finishes can include an insecticide. Look for products specifically made for use on decks.
Film-forming finishes protect wood by creating a solid barrier (film) on the surface. This type of finish includes the following:
- Paint offers great protection against water and ultraviolet light, but virtually no protection against mildew. If you want to paint your deck to enhance its appearance, consider painting only the more visible, especially vertical, parts, such as posts and railings. Coat the wood first with a water repellent preservative and liberally prime the end grain before brushing on the paint.
- Solid-color stains weather quickly on horizontal surfaces and are difficult to repair once they fail.
- Lacquer and varnish do not hold up well under sun and rain.
Redwood and cedar also need protection, especially if they contain light-colored sapwood.
- Color. To make a wooden deck the color you want, perhaps to complement your house, use an exterior stain. Even if you want a weathered look, don't simply let nature take its toll; finishes are available that protect the wood while allowing it to age in appearance.
You can also change the color of pressure-treated lumber. By letting the wood dry a bit and applying special stains, you can approximate the look of redwood or cedar. You may need to apply two coats of stain. You can buy brown pressure-treated lumber that looks similar to redwood; however, it needs to be restained regularly.
- Reduced VOCs. Volatile organic compounds, or VOCs, are the materials that evaporate as a finish cures. VOCs from wood finishes, especially from solvent-borne (oil-based) ones, have been found to be significant air pollutants. Now, low-VOC finishes are available. Water-borne finishes, such as latex paint or stain, are less harmful to the atmosphere. New products have been developed to reduce the polution, although they generally do not last as long as oil-based finishes.
Pressure-treated lumber that simulates the look of redwood costs more than the regular greenish yellow or dirty gray variety.
You will find most common penetrating finishes in the $15 to $55 per gallon price range. These will need to be reapplied regularly. Film-forming finishes can be found for $17 to $28 per gallon.