Building with composite
Hybrid lumber offers freedom and good looks for decks and other outdoor projects, but it also requires some special considerations
Wood is full of surprises, and not all of them are good. That's especially true when you're choosing wood to build outdoors. Just ask anyone who owns a deck that's more than five years old. What started out as beautiful wood is probably grey, mottled and maybe even a little mouldy. Some folks like this natural, weathered look. Other homeowners want a more refined appearance, so they opt for a finish of some kind when the deck is new.
What they probably don't realize at the time is that even today's longest-lasting deck finishes don't look respectable for more than two or three years. Sure, wood is authentic and structurally effective, but to keep wood looking good outdoors, you need to do a lot of things that are anything but natural: strip the old finish chemically, blast the brown goo off with a pressure washer, apply a deck brightener, pressure wash again, then sand the surface before applying a new finish. Complete two or three stripping and refinishing cycles and the traditional deck maintenance treadmill starts to feel pretty grim. But what are you supposed to do? It'll be at least 10 or 15 years before the wood rots enough to justify a rebuild–even longer if you designed the project well.
Composite materials promise freedom from the refinishing merry-go-round, but they're also a bit of a mystery to many do-it-yourselfers. Is the high price of composites worth it? What's it like working with them? What's it's like to live with them? Are hollow or solid composites better? The answers to these questions may surprise you. They may also make you consider choosing composite for your next deck or outdoor furniture project.
Pay now or pay later
Real wood looks better than any composite I've seen. At least, when that wood is properly finished and relatively fresh. The appearance of new composites is much more durable, even if real wood starts out more beautiful. Composites change relatively little over time.
When you buy composites, you get two things: a physical building material, plus a good measure of freedom. You don't have to buy finishing supplies and you don't have to use them. And if you add up the true costs of labour and finishing real wood over its entire lifetime, it comes out at least as expensive as composites. Sometimes composites are even cheaper than wood in the long run, depending on the value you put on refinishing.
Working with composites
When non-wood deck lumber first hit the market 20 years ago, it was 100 per cent plastic. This material was incredibly heavy and was prone to gumming up blades and bits if it overheated during a cut. It was also insanely expensive. But today's composites are different because they're just that–composites made of a blend of wood fibres and plastic. The addition of wood fibres makes the material much easier to cut, drill and rout. It also improves the appearance and underfoot traction of the product. It's easy to keep your footing on a modern, composite deck, even when it's wet, which is why I used composite to build my swim platform.
When you find you have a project that could benefit from using composites, there are some options to consider. You'll have to choose between hollow composite extrusions or solid composites. The issue isn't just about the lighter weight and lower cost of extrusions compared with solid composites; it's also about how you're going to work the material and the final look you want to achieve for your project.
Extrusion composites have hollow cores, which means they all come with end caps and strips to hide what's going on inside. No problem there, except this feature restricts your creative options. You'll need to go with a solid composite if you want to rout a bullnose profile on the overhanging edges of your boards, for instance. The same is true if you want to create custom-milled chamfers on the edges of posts or joints between deck boards.
Hollow extrusions are also much more rigid than solids, so boards can't be bent for curved designs.
I prefer solid composites to hollow extrusions because of appearance and creative options. Solids are the most like real wood. One unique challenge of working with solids, however, is the need to keep deck boards going down straight. This is true with all decks, but especially true for composites because the stuff is so flexible. The first board you lay down is especially crucial. Take all the time necessary to anchor it perfectly true because it's going to set the stage for all that will follow.
Put your composite deck or outdoor structure together right, give it an occasional scrubbing and it will serve you well. New varieties offer an enhanced appearance that looks less like plastic and more like real wood–all without the ongoing maintenance liability. A composite deck may be a little on the high-priced, high-tech side, but if it saves you time on your knees with a paintbrush, then that might be a pretty good deal.
A taut string makes an excellent straightedge for all kinds of building applications, but it's also easily deflected from accuracy. You could stretch a string from two wood screws driven into floor joists to guide the positioning of that critical first deck board, but what's the use? If any part of the deck board touches the string during work, the rest of the run is kicked out of whack.
Here's a fix: anchor only both ends of your first run of deck boards to the joists across the entire length of your deck, leaving the middle area of the boards loose for now. Next, stretch a string from one end of the run to the other, but wrap the string around a spacer block of scrap 3/4" plywood as it leaves the ends of the deck boards. This block holds the string away from the edges of the deck boards by 3/4". Grab a third piece of scrap ply of the same thickness, then slip it between the edge of the deck board temporarily as you work your way along the string, aligning the boards and anchoring them. Every time you remove this spacer block, the string is left unhindered, offering a perfectly straight reference for you to work from as you continue straightening and anchoring that critical first row of boards.
Everything in the world ages, even composites. They certainly don't age as fast as real wood, but you should take a peek inside the time machine before laying down thousands of extra dollars to avoid wood. The oldest composite decks I've seen first-hand were built in full-sun locations in the 1980s. The material was a little on the bleached side after 20-odd years, having lost some of the medium-brown colour that could still be seen on the underside of the deck boards.
Also, keep in mind that under especially moist conditions, it's possible for mould to grow on some composite deck surfaces. Mould growth is rare, and it's easier to remove than an old wood finish, but it's still a possibility.
Abrasion and dirt are another issue to consider. No deck material is immune from getting muddy, dented and rounded over in high-traffic areas.
Wood: King of strength
When it comes to joists, beams and load-bearing posts, wood is still king. That's why even mainly composite decks rely on wood underneath as support. Because composites are generally a blend of plastic and wood fibres, this combination resists weathering well, but it also tends to bend under sustained loads. A few types of load-bearing composites are beginning to appear on the market, but they're still not mainstream yet. The potential flexibility of composites is also why you need to use closer-than-usual joist spacing to support closer than usual deck floors. Find out your manufacturer's maximum spacing specifications before you plan your deck framework.
Since composites don't have knots and wood-grain variations to distract your eye, ordinary deck screws driven from the top of each board down can look pretty obvious and a bit unsightly. That's why you should consider invisible anchoring systems for your project.
Invisible fastener systems make decks look much better, but this benefit usually comes with two considerable drawbacks: high cost for the hardware and much slower installation time. I haven't tried enough different systems to tell you which is best, but I'm currently using hardware called IQ hidden fastening system. The fasteners are comparatively quick to install, they regulate board-to-board gaps and hold the deck boards up off the top edge of the joists a bit, helping water drainage and the rot resistance of the wood.