What are the options for finishing a deck?

Q: What are my options for finishing an existing deck? I have a 3-year-old upper deck and a newer lower deck installed last summer. Both are made from pressure-treated lumber and neither have been stained or finished. When's the best time to do the job? Is sanding or pressure washing the best preparation? Specifically, what are the longest lasting deck finishing products?

A: Finishing a deck is a lot like getting married. The results of your choice have very long-term consequences. And in the case of a deck, you've got to choose one of three forks in the road. You can leave the wood unfinished, you can apply a product that adds transparent colour and a surface film, or you can apply an opaque deck finish that looks a lot like paint.

Leaving the wood unfinished is the easiest option and doesn't shorten the life of the wood appreciably. That said, not everyone likes the look of barn board grey, and that's what your deck will look like in a few years.

If you do opt for any kind of finish, then the minimum preparation you need to complete is pressure washing the deck. You'll be better off if you also sand the deck using an 80-grit abrasive after the wood is completely dry. The combination of washing and sanding maximizes absorbency of the wood, allowing the finish to get a good strong foothold. This kind of preparation can double the finish life compared with unprepped wood.

When it comes to choosing a finish, you need to understand that many brand name products perform extremely poorly according to independent testing. The most durable deck finishes on the market right now are opaque and look like paint. A deck finish survey that's been underway continually at Consumer Reports magazine for many years currently lists Cabot Decking Stain as the toughest, most durable deck finish on the market. It's opaque. The longest lasting semi-transparent deck product available in Canada right now is Sikkens Cetol SRD. It rates 'fair' in appearance after three years of exposure. Regardless of which finish you choose, understand that you’ll need to strip and refinish at least every three years. That's the fact that prompts some people to go the no-finish route.