What’s the best way to apply a long-lasting finish to a new wooden deck I’ll be building this summer?
It’s a good thing you asked because 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 people tell me 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 common experience for deck owners across America, though it doesn’t have to be. Successful deck finishing depends on understanding crucial factors that aren’t obvious (and rarely explained fully) on product labels. But after you address the key issues, your wooden deck can have long-lasting beauty.
Regardless of the product you choose, 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 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 finish you choose is more important than you might guess. According to independent consumer testing, most deck finishes fail quickly, even if applied as directed. That’s because sunlight, moisture, mildew and abrasion all make a wooden deck the world’s most challenging surface to finish. Two products I’ve had personal experience with are Sikkens DEK and Cabot decking stain.
Reapplication of a deck finish is necessary over time, 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 prone to peeling 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 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 a new coat of finish. A variable speed sander works really well for this situation. By turning the speed to a crawl, you’ll gain excellent control of the abrasive action. In fact, I’ve found decks actually look nicer than new after a light sanding, a careful cleaning and a touch-up coat.
Contributing Editor Steve Maxwell has been helping people renovate, build and maintain their homes for more than two decades. “Canada’s Handiest Man” is an award-winning home improvement authority and woodworking expert. Contact him by visiting his website and the blog, Maxwell’s House. You also can follow him on Twitter, like him on Facebook and find him on Google+.