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:
Film-forming finishes protect wood by creating a solid barrier (film) on the surface. This type of finish includes the following:
Redwood and cedar also need protection, especially if they contain light-colored sapwood.
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.
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.