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You can make simple cross cuts in composite decking the same way you would cut any soft pine—a power circular saw will work fine. A power miter saw can provide very accurate, straight cuts, and a table saw with support extensions can make all types of cutting easier. Carbide tipped blades are suggested—the fewer teeth the better for smooth cuts. Don’t allow blades to get overly hot when cutting as this can cause cuts to be warped or wavy.
Ripping a composite board (cutting lengthwise) is trickier. Even the most experienced carpenters have found that when the power saw’s blade heats up, it creates slight waves along the cut line. Whenever possible, try to avoid ripping composite decking and use full boards for your surface. If you do have to rip, put the rough, exposed cut side where flaws will be least noticeable.
If installing the decking around an existing structure, a simple router can be used to make curved cuts. Again, treat the material just like you would soft pine.
A clean cut should not leave any loose material, but if you need to clean up an edge, do not use a sander. Sanders will mar the finish and in many cases void your warranty. A hand coping saw will work well to smooth finished edges if needed.
One of the most critical steps for properly securing composite decking in place is to make sure you have at least a 1/8-inch gap between the decking boards. This space (approximately equal to the width of a 16-penny nail) is important for two reasons. First, it allows for proper drainage and keeps the deck cleaner, safer, and less prone to moisture problems. Second, because composite decking expands in hot weather, the space ensures that extra stress won’t be placed on the fasteners.
Extra spacing is also important between board ends and a wall when decking runs perpendicular to the wall. Leave a healthy 1/2-inch gap at the ends to ensure the material can expand and contract without coming into contact with the wall. This will increase the longevity of the deck and also prevent bowing during the hottest part of the day.
Composite decking can be fastened to treated wood joists with screws or with hidden fasteners. Using composite deck screws is critical becaues they are specially designed to help hold the material in place. Though common wood screws might seem like they would work as well, they tend to “mushroom,” or bore out the holes rather than set into the material. Composite deck screws are designed so that they do not push the material out and will create a much more uniform and tight fit.
Though composite decking is more stable than regular pine, it still can break when driving fasteners close to the edges. Pre-drilling pilot holes can prevent this from happening and make installation go much faster and smoother. Instead of pilot holes, some manufacturers suggest drilling a starter hole about 1/8 inch deep into the material. Select a bit size that is the same diameter as the screw’s inner core and take care not to go too deep into the material.
Countersink the screws but no deeper than the screw’s head. Besides creating a rougher finish, deep countersinking can reduce the effectiveness of the fastener and void the warranty. It is also important that all screws be secured at a 90-degree angle to the boards. Fastening from the side can cause dimpling in the composite surface and mar the finish.
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