Despite the increasing popularity of composite decking in recent years, these manufactured products possess some major flaws. Particularly when you compare them to the organic materials they’re meant to replace, composites simply don’t measure up. While these products might appear similar to the tropical hardwood lumber they replace, the similarities don’t even go beyond the surface level.
The material typically used for the outer shell of composite decking is polyethylene, the same plastic used for disposable water bottles; it’s a pretty weak plastic. Sometimes used instead, polypropylene is a tougher substance, but it is still plastic. This water-resistant outer shell, or cap stock, shields the vulnerable wood flour core from mold and decay; however, this shell is extremely thin. When the delicate surface is scratched, appearance is far from the main concern: the inner core is exposed to moisture and mold. For this reason, most manufacturers warn against using metal snow shovels on composite decking.
Unlike Ipe, which has a Class A fire rating, composite decking is quite susceptible to fire damage. Like all plastics, it reacts to intense heat by melting, which causes the release of toxic gases into the air. Replacing deformed boards means an unevenly sun-bleached deck as well as disposal of the unusable boards into landfills, where they will remain for hundreds or even thousands of years. Not only are tropical hardwoods more resilient to fire, but they can be easily replaced and finished to match the surrounding decking. What’s more, the damaged boards will easily biodegrade in about a decade.
While you may contest that scratching or fire damage can be avoided, seasonal shifts in temperature and moisture levels are inevitable. Seasonal movement of traditional lumber is unavoidable but predictable. Wood moves noticeably across the grain, but almost imperceptibly along the grain. Based on lumber species, we can even estimate the amount of movement to a high degree of accuracy. By contrast, composite decking lacks grain patterns to allow for predictable expansion. Instead, both the plastic shell and inner core of composite decking expand in all directions when exposed to heat. As the plastic shell is stretched with the core’s expansion, it retains the larger size even once the wood flour shrinks back to its original size. The result is separation of the core from the shell, producing uneven warping along the board lengths, with the ends swelling to a greater degree than the interiors. When cut ends occur throughout the structure instead of only at the ends, this issue is even more noticeable. The swelling and moisture traps will end up requiring widespread board replacement, again landing many pieces in landfills.
A simple way to avoid these and other pitfalls of composite decking is to take a look at the attractive and durable species of tropical hardwood decking. J. Gibson McIlvain highly recommends Ipe and Cumaru and carries a wide variety of board lengths and widths for decking purposes.
J. Gibson McIlvain Company
Since 1798, when Hugh McIlvain established a lumber business near Philadelphia, the McIlvain family has immersed itself in the premium import and domestic lumber industry. With its headquarters located just outside of Baltimore, the J. Gibson McIlvain Company (www.mcilvain.com) is one of the largest U.S. importers of exotic woods. As an active supporter of sustainable lumber practices, the J. Gibson McIlvain Company has provided fine lumber for notable projects throughout the world, including the White House, Capitol building, Supreme Court, and the Smithsonian museums.
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