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If you're the owner of a new wooden deck (or plan to be), there's something a whole bunch of experienced deck owners want to warn you about.: It's not easy to create a long-lasting deck finish. Many have stories about peeling, fading, mildew and deterioration of their decks, all within a year or two of brushing on hundreds of dollars worth of finish. This is actually a very common experience for wooden deck owners across Canada, though it doesn't have to be. The fact is, effort and expense are not, in themselves, enough to give you a deck you can be proud of. Deck finishing success depends on understanding crucial factors that aren't obvious and rarely explained fully on instruction labels. The good news is, once you've address the key issues, your wooden deck can have long-lasting beauty.
The first thing to realize is that regardless of the product you apply, the pores of new wood have to be opened to allow full penetration of any finish. New lumber has poor surface absorbency because of a surface condition called mill glaze -- a side-effect of the planing process. If mill glaze is not removed it'll inhibit finish penetration and increase the risk of peeling. The best way to deglaze wood is by sanding with a 60 or 80-grit abrasive in a random orbit sander. Pressure-washing is the second-best option according to lab studies. Random orbit sanders suitable for deck duty (or any large outdoor surface) are shaped like an autobody grinder and have variable speed capabilities. I bought a Porter-Cable 7336 five years ago and I still love it after sanding hundreds of square feet of wood. More on this later.
The finishing product you choose is more important than you might think. An ongoing, 4-year deck finish test by a leading consumer advocacy group shows startling results. Of the dozens of formulations originally included in the test, only a handful still remain.
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Most were dropped because they performed too poorly. Just because a product has been brought to market in a fancy container doesn't mean it can stand the sunlight, moisture, mildew and abrasion that makes a wooden deck the world's most challenging surface to finish. Some fail miserably. My favorite deck finish is Sikkens DEK, a tinted, translucent film-forming finish. I've used it successfully for years. Just remember to sand before application, don't overcoat the product (which will lead to peeling), and don't use it on surfaces that get wet continually. Cabot's Decking Stain is an opaque finish that also has shown excellent results in independent product trials.
Maintenance of any deck finish is necessary, but simply applying more of what you put on initially isn't enough. This is especially true with film-forming products that get thicker and more peel-prone as multiple coats build.
The way around this problem is to sand the old finish lightly with a 220-grit abrasive in a random orbit sander, at slow speeds, before applying a maintenance re-coat every 18 to 36 months. You don't want to go right through the old finish, just remove the blistered areas (usually around knots) and roughen up the entire surface before wiping off the dust and applying another coat of finish. This is where a variable speed sander shines. By turning the revs down to a crawl, you'll gain excellent control of the abrasive action. In fact, I've found that decks actually look nicer than new after a light sanding, a careful cleaning and a top-up coat.
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