If you are wondering why you can’t use just any finish on your deck, think about the abuse decking must handle, including pounding rain, snow, and ice, abrasion from traffic and furniture, and often many hours of direct sun, day after day. To make matters worse, the joints between the many parts of a deck retain moisture long after the rain stops, making the wood vulnerable to rot, mildew, and wood-munching insects. To combat this barrage, deck-finish manufacturers offer a variety of formulations that include sealers, preservatives, UV-light inhibitors, pigments, and resins. Some are oil based and penetrating. Some are acrylic and film forming. Others are a mix. Here is a list of the most popular finishing options for a new deck:
Clear sealers, or water-repellent preservatives, are the most popular choice for new decks. They help protect wood from moisture, thereby saving it from repeated cycles of soaking up water and then drying out. Unprotected, wood will crack, warp, cup and splinter. Sealers must be reapplied regularly to remain effective then; the wood will weather to gray. Water- repellent preservatives contain a fungicide to fight mildew.
Toners, or transparent stains, offer more than clear sealers. They deepen and enhance the wood, and the grain remains visible. You can use finishes on pressure-treated wood to approximate the look of more expensive woods. The best products in this category penetrate the wood surface, protect it from UV light and mildew, and leave a substantial top layer to resist moisture. They are relatively expensive finishes but will retain the original color of most woods strictly according to the manufacturer’s directions. Note: Exotic hardwoods like Ipe or mahogany are dense with natural oils and don’t absorb penetrating stains as well as softer woods. Allow them to weather to a teak-like gray or treat them with a hardwood-specific finish according to the manufacturer’s recommendations to maintain the original wood color.
Semitransparent stains generally have more pigment than transparent stains and do a better job of hiding imperfections and unattractive grain patterns. Alkyd- and oil-based versions excel because they penetrate the wood better than acrylic formulations. All are available in a wide variety of wood tones and colors.
Solid stains are more heavily pigmented than semitransparent stains. (Think thinned paint.) They offer superior protection against UV rays and hide the color and grain of the wood. They, too, come in a wide variety of colors. Oil-based products usually last longer, but water-based formulas are easier to clean. Expect wear patterns to show in heavily-trafficked areas.
Deck and porch paints, unlike many stains, are film-forming products. This makes for superior UV and moisture protection, and is great for camouflaging lesser grades of lumber—but paint may blister and peel, and will eventually show wear in high-traffic areas. Use paint if you want a bright gloss or semi gloss finish to match or complement paint on your house exterior. Acrylic- and alkyd-based paints are available and should be applied over an oil-based primer. Mix the paint with clean sand to improve slip resistance if desired. Keep painted decks swept free of dirt (it wears finishes away faster), or place outdoor carpets along traffic paths to prevent wear. Sand and recoat as necessary.
Preservatives prevent fungal growth, rot, and decay— and some also protect against wood-boring insects. They are recommended for treating untreated wood as well as the site-cut ends of pressure-treated lumber. Preservatives alone are not finishes. They may, however, be sold in combination with sealers to provide moisture protection as well, making them a one-step finish. Some preservatives can be used prior to applying paint for added protection against rot and decay.
Apply one thin coat of finish to penetrate and dry completely. Thick layers of finish don’t penetrate nor dry completely. The wood should be dry before applying finish. Sprinkle a little water on the deck. If it soaks in immediately, the wood is dry enough for finish application. New pressure-treated lumber must dry out completely before finish is applied. Check with the lumber supplier for the proper amount of drying time.
Make sure whatever finish you apply is rated for outdoor use and for a deck surface. Follow manufacturer’s application instructions for best results. And don’t spray or paint yourself into a corner.
Use a deck brightener to clean a deck before applying new finish (page 184). A brightener removes dirt, mildew, and the top layer of sun-faded wood fibers to restore the natural color of cedar and redwood.
Reapply finish to decks approximately once a year. Harsh climates and heavy deck usage may require reapplication twice a year.
