Building with composite
Hybrid lumber offers freedom and good looks for decks and other outdoor projects, but it also requires some special considerations
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.