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How to Build a Composite Deck

Composite deck lumber is good stuff, it’s getting better and it’s getting more popular. Made by dozens of different companies, composites are the most popular type of synthetic deck lumber right now. Composites get their name from the combination of wood fibres and plastic used to make them, though 100% plastic deck lumber exists, too. That’s why the proper blanket term is “synthetics”. Either way, the idea is to deliver a no-finish, no-rot deck surface that continues to look terrific over the years with minimal care. I’ve worked with synthetic deck lumber since 2001 and I use it whenever I can today. Higher prices than wood usually scare people away from composites, but this fear isn’t justified.

Here are a few tips to help you make the most of building composite decks, beginning with the people side of things.

Tip#1: Educate Your Clients

Ultimately, composite deck lumber is all about making clients happier, and that’s where a story I hear often comes in. A homeowner gets a new wooden deck and is pleased with the result, but not for long. After a couple of years, the homeowner grows weary of failing wood deck finishes and resents the maintenance that refinishing demands. This is when regret kicks in. The money they saved going with wood never makes them feel better, either.

Financially speaking, the higher price tag of composites pays off with freedom from refinishing costs and freedom of the annoyance of a ratty wooden deck that should have been refinished last year. Synthetic decks still need to be cleaned, but the required maintenance is far less than wood.

Tip#2: Select the Right Synthetic

There are three simple things to remember here:
1. Composites are a blend of plastic and wood fibers.
2. Plastic lumber (usually PVC) is 100% wood-free.
3. Both types can be worked with regular tools and they come in solid and hollow versions.

I like solid composites best because they can be routed and shaped just like wood, with no need for end caps. Hollow composites are cheaper, but they don’t look as nice in my book. Either way, no synthetic lumber is strong enough for the superstructure of a deck. For now, when it comes to joists, load-bearing posts and beams, wood remains king.

Tip#3: Use Invisible Fasteners

When fastening any kind of synthetic lumber to a deck frame, use hidden fasteners. If you drive a screw into the top face of any synthetic material, it creates an unsightly berm of displaced plastic around the hole. Some synthetic lumber systems come with a hidden fastening system engineered right in, while others need separate hardware. Yes, it’s sometimes possible to hammer down the berm of composite that forms around the head of conventional deck screws, but it doesn’t look great. It’s a shortcut that looks like a shortcut.

Regardless of the hidden fastener system you use, you’ll have to face-drive screws on the outer boards and places where hidden hardware won’t work. It’s no good to have visible screw heads here though when the rest of the deck is screw-free. This is where a woodworking trick can help.

Counterbore holes for ordinary screws, drive them in then cover the screw heads with tapered plugs you make from scraps of the synthetic material you’re using. Custom-grind the sides of a spade bit so it drills a hole that holds the plug firmly as it’s tapped into place. Use a little outdoor wood glue on the edges of the hole before driving the plugs with glue and they won’t ever come loose.
Tapered plugs too labor-intensive? Special, small-headed screws colored to match specific synthetic lumber are much faster. They don’t look quite as good as tapered plugs, but they aren’t too noticeable from a distance. ​
Double Joists and Routed End Cuts

Take time to decide where deck board joints will go, then install double joists with a 1-inch space between them. This lets you keep fasteners well away from the ends of deck boards, especially considering that synthetics need expansion gaps between board ends because they expand so much in the sun. While you’re at it, take the time to rout a small chamfer on the cut ends of deck boards. The look is very refined for minimal extra time and effort. All else being equal, the higher price tag of a deck with synthetic surfaces makes more profit for you. Another advantage of synthetics is that the material is more consistent than wood. You don’t need to order extra to allow for the inevitably bad boards you’ll get with regular lumber. The higher price of the material will also allow you more room for mark-up on the project.

Educate your clients on the benefits of synthetics, then treat this material with greater care than ordinary 2x6s. You’ll have a long-term happy client, you’ll leave a legacy of great decks, and you might just make more profit on the job.​