I’ve talked about how composite decking is made. To summarize, it’s a mixture of wood fibers and plastic.
Now, while the plastic is supposed to keep water away from the wood, imperfect production methods can still let moisture in. This results in a familiar scenario if you’re used to working with wood decking: expansion. The wood fibers absorb water like a sponge, causing the entire board to swell. When the sun comes out and the board dries, it shrinks back.
This expansion/contraction cycle isn’t very forgiving on the rigid plastic component of composite decking, and the result can be anything from ugly—flaking surfaces like the one pictured below—to dangerous. The board can crack down the middle, compromising its durability under regular foot traffic. This deteriorating process is sometimes referred to as delamination.
This problem is so widespread, in 2009 the U.S. Consumer Product Safety Commission issued a recall on composite deck boards. Even more recently, reports keep coming in of injuries due to composite decking failure.