As superior as tropical decking is to composite decking in general, the impact of choosing an inferior product is multiplied when you’re building a large-scale structure such as a boardwalk. In Part 1, we looked at 4 major problems with building boardwalks with composite decking materials: inferior hardness, heat retention, oily surface, and unpredictable movement. As significant as those issues may be, they’re just the beginning!
Reason 5: Inferior Strength
Composite materials vary when it comes to strength, but if you check out the installation manuals from just about any manufacturer, you’ll notice that they recommend installing their decking boards on 12” center joists. The more common spacing of 16” for boardwalks will likely result in bounce (initially) and then deformation over time. The issue of bounce is more significant with composite materials, too, since once plastic is deformed, it won’t regain its initial shape. The wood flour core is far from strong; instead, it relies heavily on the outer plastic shell. If that plastic shell becomes compromised, the strength of the entire board is compromised. With the high amount of foot traffic that a boardwalk receives during the summer, bounce and deformation are bound to occur. However, installing boards on 12-inch centers would clearly cause an enormous increase in the cost of any project, but especially for a sizeable beachfront boardwalk.
Reason 6: Compromised by Moisture and Mold
Did you know that today’s composite decking isn’t actually resistant to weather or mold? The first composite decking products on the market were different than that which we see today. Early composite decking boards were comprised of a mixture of PVC or polyethylene with wood flour; however, that composition was quickly abandoned, since even bound with plastic, wood fibers can absorb moisture quickly and easily. Of course, real wood can do that too, but it does so in a predictable fashion, thanks to the structures which nature uses to feed the tree; real wood also includes resins that protect the wood against mold and insects. Wood flour found in composite decking, however, eliminates those structures and resins. The resulting ground-up wood includes cellulose, broken down structures on which mold can easily feed.
In order to delay or reduce this inevitable breakdown of the wood flour, composite decking now encases a wood flour core in plastic “cap stock,” intended to block out moisture from the easily compromised core. Contrary to the manufacturers’ intention, though, the situation is even more bleak than before. Now any puncture of the cap stock — which occurs even during installation — causes the inner core to be exposed to the elements. Not only can mold and decay easily affect the board, but they also cause the shell to crack or separate from the core, acting to further compromise the weather resistance and strength of the board.
Continue with Part 3.
Read the Series
• Composite Decking or Tropical Decking: Which Is Best for Boardwalks? Part 1
• Composite Decking or Tropical Decking: Which Is Best for Boardwalks? Part 2
• Composite Decking or Tropical Decking: Which Is Best for Boardwalks? Part 3
J. Gibson McIlvain Company
Since 1798, when Hugh McIlvain established a lumber business near Philadelphia, the McIlvain family has been immersed 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.
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