Any wood—even pressure-treated wood—will eventually dry out, crack, and turn gray if left exposed to the elements. To protect your investment and keep your deck looking its best, finish it with a clear water-repellant sealer, a stain, or paint. To ensure long life, all surfaces of decking boards should be treated before installation.
Pressure-treated wood used for structural components resists the effects of weathering. If it turns gray and displays some minor cracks, it won't detract from the beauty of your deck because it's usually hidden from view. Even so, it's a good idea to finish the ends of structural lumber with a water sealer. The chemicals used to produce pressure-treated lumber sometimes don't soak all the way to the centers of the boards. Treating the ends protects against moisture penetration and ensures the longest possible life for your deck.
A deck with two kinds of wood finishes is common and requires two maintenance schedules. In this case, the cedar decking should be cleaned and resealed once a year, while the painted railings need recoating about every three years.
Clear Finishes Clear finishes seal wood against moisture and help prolong its beauty. Clear wood finishes with ultraviolet (UV) blockers help prevent decks from turning gray, but after many years, some graying is inevitable. The best way to keep wood decking looking fresh is to scrub it thoroughly at least once a year with a commercial deck-cleaning agent designed to restore the natural color to the wood. Then seal the decking. Clear finishes with mildewcide are called water-repellent preservatives and help prevent the growth of surface mildew.
Deck Stain Alter the appearance of a deck with wood stains or paints specially formulated for use on decking. Oil-base and water-base stains color the wood and protect it from the effects of moisture and sun. Semitransparent stains let the pattern of the grain show through. Solid wood stains hide the grain pattern and mask flaws. Test the stain on a scrap piece to make sure you like the final appearance. You can use deck stain on pressure-treated wood, but because this type of material already is impregnated with a color—either green or brown—it's especially important to test scrap pieces before committing to the final look. Stain can be reapplied every two or three years to freshen the appearance of the deck. Clean the decking thoroughly before reapplying stain.
Deck Paint Deck paints are specially formulated to withstand weather. As with any paint, exposure to the elements eventually will result in cracking and peeling. Maintaining the appearance of painted surfaces requires periodic scraping, sanding, and recoating.
If specified by the manufacturer, deck paints are resistant to foot traffic and can be used on decking boards. However, this is a harsh test for even the most durable paint. To add color, consider painting railings, fascia, overheads, and built-ins, and finishing decking boards with clear sealers or stains.
Finishing Techniques Decking materials should be dry before painting—but not too dry. Left in the sun without protection, the moisture content of lumber will evaporate quickly, often resulting in split, warped wood. On the other hand, decking materials are often freshly milled and full of moisture, making it difficult for sealers or stains to penetrate into the grain. The key is timing. Wood is ready for finishing if it quickly absorbs a few drops of water sprinkled on its surface.
Before finishing lumber, cover nearby plants, structures, and landscaping features with plastic sheets or drop cloths. Sealers, stains, and paints can be applied with a brush, a roller, or a sprayer. A roller attached to an extension pole allows you to stand while working, shortening application time. A sprayer coats quickly but sometimes not evenly. Watch for dry spots and recoat them if necessary. Spread puddles with a brush or roller to evenly distribute the finish.
Avoid painting if the weather is very hot or humid. Either of these conditions can cause the paint to fail to adhere properly to the lumber. Always use a top-quality primer as the initial coat. Latex primers work well and clean up easily, but oil primers tend to penetrate into the wood more completely, creating a tighter, longer-lasting bond.