By Roy Berendsohn and David Agrell Mar 14, 2014 @ 10:30 AM
I’m thinking of replacing my wood deck with composite lumber because I’d like it to be maintenance-free. I’ve never worked with this material before. What can I expect?
People choose woodplastic composite (WPC) or even plastic lumber (PL) over wood because they want the finished project to resist rot, wood-eating insects, harsh sunlight, and mold and mildew, and they never want to paint it. So, do these materials deliver? In many respects, yes. But are they maintenance-free? No material is. Though many of these products carry 25- to 50-year warranties that protect against things like rotting, splitting, peeling, and insect infestation, we’ve seen these decks fade, buckle, and harbor mildew in certain conditions especially the stuff that contains wood fibers. But, generally speaking, WPC and PL decks don’t require the annual makeover that wood decks do, and most last for decades with little more work than soap and water rinses. Expect to pay around $3 per linear foot for 1 x 6 decking material, which puts it somewhere between the cost of western red cedar and ipe lumber.
WPC and PL products usually contain a thermoplastic, such as polyethylene, that has been recycled from old plastic bottles and bags. Composite lumbers add other materials such as wood flour, sawdust, or ground-up peanut shells. They can be solid throughout, or they may have a hollow, ribbed center to reduce weight. (Some solid-core products can weigh as much as 5 pounds per foot, which is three times the weight of cedar.) High-end composite decking is often encased in a plastic shell that resists fading, staining, scratching, and mold.
It’s important to look at the manufacturer’s directions before installing this material. When it gets warm, it expands more than wood along its length but less across its width. The longer the piece of decking, the greater its expansion and the more you have to account for this when building your deck. Check the product’s end-gap chart, which correlates the space needed between the ends of two decking pieces with the length of each piece, the temperature during installation, and the highest ambient temperature you expect in the deck area. For example, a 12-foot-long piece of Bear Board PL installed at 60 degrees Fahrenheit could expand by as much as 1/8 inch on each end of the board, so you’ll need a 1/4-inch gap between the ends of two boards. Blow this critical design detail and your decking could buckle on a hot day.
Keep in mind that, compared with wood, this stuff is bendy. Don’t just assume it can span joists on 16-inch centers. Some are engineered to work on 12-inch centers. The flip side is that you can create curvy designs not possible with wood lumber.
You can use standard woodworking tools to cut, drill, and fasten this lumber, though we recommend carbide-tipped blades, which stay sharper longer. Use a moderate feed pressure to avoid melting the plastic or jamming the cutting tool. If the manufacturer recommends predrilling screw holes, do so. Some lumber has grooves milled along its edges for installing hidden fasteners that allow the material to move with temperature changes. You can also drive decking screws or stainless-steel trim-head screws through the top of the board, but be warned: This allows moisture to seep into the wood fibers, which can lead to rotting.
Finally, most consumer-grade WPC and PL can’t be used structurally, such as for joists or corner posts. For those you’ll need a specially engineered plastic lumber that has been fortified with fiberglass. Make sure you use the material as the manufacturer intends or you’ll void its warranty.