The Hamilton Spectator, Steve Maxwell: September 10, 2005

Surface matters; Wooden decks take knowledge to finish well
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 tell 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. The fact is, effort and expense are not, in themselves, enough to give you a deck you can be proud of.

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 mill glaze -- a side-effect of planing. 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. Random orbit sanders suitable for deck duty are shaped like an autobody grinder and have variable speed capabilities.

The finishing product you choose is more important than you think. An ongoing, four-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. Most were dropped because they performed too poorly. Just because a product has been brought to market 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 favourite 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 recoat 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.

Send questions to smaxwell@onlink.net or go to workshoptalk.com.