Secrets to successful outdoor woodwork

If you build outdoor furniture the same way you build indoor projects, you’re headed for grief. I know, because I’ve experienced plenty of heartache learning things the hard way. Finishes that don’t last, joints that fall apart and corrosion-stained surfaces are all common and disappointing fates that afflict outdoor furniture. Common, but not unavoidable–at least, not if you follow my field-proven design and construction tips.

Moisture and sunlight are the enemies that you must deal with at the start. Cedar is such a popular choice for outdoor projects because it keeps these foes at bay: it’s rot-resistant and long-lasting. Yet, cedar also has weaknesses. It’s particularly soft and structurally weak, which creates problems you must address when you build.

Cedar needs large, overlapping joint areas and a lot of help from fasteners and glue if it’s to hold together for the long haul outdoors. Avoid mortise-and-tenons and dowel joints. Even lap joints can fail unless they’re cut in extra thick wood.

Keeping your wood in good condition

Since cedar dents easily, I recommend you rout corners with a round­over or chamfer bit. Also, square edges don’t hold a finish as well as rounded or angled ones, and as your finish wears out at the corners, deterioration spreads to surrounding areas.

Leave any 3/4"-thick lumber outdoors for a couple of years and it’ll almost certainly develop a cupped shape across the width of the boards. This change happens as the wood gets sopping wet and then bone dry over the course of each year. That’s also why beefy lumber–thicker than 1"–is my choice for most outdoor applications. It’s much less likely to cup as it ages.

Large-diameter wood screws (I prefer #10) work best with cedar because the wood is so soft. But even these should be supplemented with weatherproof glue, and not just for strength. Ordinary wood glues–even those rated as water-resistant–go mushy during damp, outdoor weather. You need to use glues that meet the waterproof rating set by the American National Standards Institute (ANSI). For example, a glue that ANSI rates as Type II is suitable for outdoors. A Type I glue actually has a higher waterproof rating than Type II. So if you can, use Type I.

Adding glue to all joints on your outdoor furniture and using screws, nails and bolts makes the overall project much more rigid. Glue also helps to make projects last longer because of its ability to seal out water. When moisture makes its way into overlapping pieces of wood, it can keep joint areas wet for a long time. The longer wood stays wet, the more vigorously microbes work to break it down.

When applying glue to an outdoor project, aim for full coverage of the joint area. Also, as you design outdoor furniture, eliminate small gaps between parts. In many areas of Canada, these spaces offer an open invitation to European earwigs, insect pests that leave behind mounds of droppings that hold water and promote rapid rotting because of the nutrients they contain. Besides, who wants to sit on a lawn chair loaded with bug manure?

Fastener choice is another key issue. Although most screws and nails are coated with some kind of silver, golden or green material that implies corrosion resistance, few metal fasteners resist both corrosion and long-term staining successfully. Ordinary electroplated wood screws certainly can’t deliver, and even fasteners rated for deck applications can cause staining over time. This might not be an issue on the deck on which you park your barbecue, but it can matter on a chair, lounge or outdoor table you care about.

I’m a fan of stainless-steel fasteners because they address the problem you encounter with other fasteners. Screws, finishing nails and framing nails are all available in corrosionproof stainless steel. For outdoor furniture joints that require larger fasteners, choose hot-dipped galvanized carriage bolts. These have a dull grey surface that performs almost as well as stainless steel. Whatever you do, be sure to avoid shiny silver electroplated bolts, nuts and washers. These are more common than hot-dipped galvanized and cost less, although they also corrode and stain wood fairly quickly.

Does all of this seem like too much detail? I used to think so too. Now, I know better, and I enjoy all my outdoor projects more because of it.

Outdoor finishes

You can choose the right fasteners, joint designs and corner profiles, yet still have your outdoor projects drive you crazy if you make inappropriate finishing choices. All outdoor finishes are destined to fail. The real question isn’t just how long a finish lasts, but how easy it is to renew. This element is especially important with chairs, benches or any project that has many gaps and interior corners. Imagine what it would be like to scrape peeling urethane or paint from those types of surfaces and you’ll see the logic behind finishes that form no surface film.

Exterior-grade oils fit into this category. Although they need to be renewed annually, the job’s easy. Leaving outdoor wood bare and finish-free is even easier still. Sure, the wood will turn grey, but it’ll last just as long and won’t make any demands of you over the years.


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