How to Preserve Your Deck
One of the best ways to protect your outdoor wood surfaces is to use a high-quality, oil-based wood preservative. Using an oil-based wood preservative with ultraviolet inhibitors keeps your deck surfaces looking newer longer.
Unlike paint, oil doesn’t lay on the surface; it penetrates deeply into the pores of the wood, preventing the attack of moisture from within. Oil also penetrates between joints and connections. With oil, there is no rigid surface layer (as there is with paint) that can bubble or split. However, oil eventually evaporates out of the wood, leaving it unprotected. If you use an oil preservative, you need to recoat your wood every 12 to 18 months.
Excessive amounts of oil can puddle, and puddled oil doesn’t dry. Plus, puddling scuffs easily and can stick to furniture, feet, and shoes — meaning the destruction of interior floors. So when you oil horizontal surfaces (especially decks), take care: They’re less forgiving than vertical surfaces (such as fences, posts, and rails).
Help force the oil or oil stain into the surface by going back over the entire area with a paintbrush or roller (called back-brushing). A China-bristle or natural-bristle paintbrush is by far the best applicator for use with oil. Don’t use a nylon paintbrush with oils, oil stains, or oil-based paints.
You can also make your own wood preservative at home. You need:
Boiled linseed oil
Pigment (the kind used to color paint)
Mildicide (a pesticide that kills mildew; it’s available at paint stores)
Mix equal parts of oil and mineral spirits. Then add pigment to the intensity you like, and stir in a package of mildicide. (Follow the instructions for the mildicide as if you were adding it to an equal volume of paint.)
When applying the preservative, don’t put it on too thick. A little bit goes a long way.
If you opt for stain, choose one designed for the surface you want to cover:
Horizontal surfaces: Well-meaning do-it-yourselfers often end up applying stains designed for vertical surfaces (such as siding, trellises, and fences) on horizontal surfaces (such as decks, porches, and steps). But if you want to stain a horizontal surface, look for a product designed specifically for decks. Deck stains are made to resist scuffing where lots of traffic is expected.
A semitransparent, oil-based stain is a good bet. The combination of oil and a pigment protects the wood from both sun and water and hides surface irregularities. Plan to spend in the neighborhood of $35 to $55 per gallon on semitransparent, oil-based stain. A gallon covers approximately 300 to 500 square feet.
Vertical surfaces: Stains designed for use on vertical surfaces are not as abrasion resistant as those made for decks. A semitransparent stain shows off the beauty of the wood because you can see through the stain. A solid-color stain won’t show through, but the solid color protects the wood for a longer period of time. Solid-color stain is not like paint; it looks like paint and acts like stain — full coverage, but without the pitting, chipping, splitting or bubbling.
Always apply an oil or oil-stain finish (wood preservative) either early or late in the day when the wood is not in full sun. The thinner that helps the oil penetrate evaporates quickly on hot days and can reduce the viscosity of the oil to a glue-like mess. Oil that’s too thick will end up laying on the surface. One to three very thin applications of a high-quality product may be required.
If you like the natural color of the wood that you want to protect, and you don’t want to alter its appearance, try a clear finish. Just be sure that the clear finish that you purchase contains UV inhibitors to fight off an ultraviolet sunburn.
Beware of the popular cure-all water seals. Many of these products contain petroleum jelly or paraffin, which offer minimal water protection and absolutely no UV protection. Furthermore, these products have little penetration and rapidly evaporate.