The first article of this three-part series explored some of the safety hazards associated with using composite decking materials to construct boardwalks. This next installment will explain some of the other structural problems with this type of material that could make it an inferior choice compared to natural hardwoods.
1. Composite Decking Materials Are Often Weaker Than Wood
Many composite material manufacturers recommend installing decking boards on 12” center joists as opposed to the normal 16” centers. This is because the material lacks the strength of many hardwoods which are typically used for constructing boardwalks.
Manufacturers know that if there is any sort of breach to the outer plastic surface of a composite decking plank, the inner material can weaken rapidly. A construction adjustment like this one (positioning joists 12″ apart instead of 16″) can significantly increase the cost of boardwalk installation if you choose to go with composite materials.
During the summer months, boardwalks are a popular spot for large numbers of tourists to stroll. This constant traffic can wreak havoc on boardwalks constructed from composite decking. Once the boards suffer any kind of major bounce due to encountering significant amounts of weight, they can easily become deformed.
2. Composite Decking Materials Tend to Have Erratic Movement Patterns
Composite decking manufacturers often point out the fact that wood moves, while their products allegedly remain stable. However, they’re not telling the whole story. While it’s true that wood products will inevitably move, their movement pattern is predictable. The bulk of wood’s movement will always tend to be across the grain. Because the movement patterns of different types of wood have been observed for centuries, they’re predictable. Smart builders know how to work with various woods in order to effectively mitigate any potential negative effects of the movement.
When it comes to composite materials, however, there is still movement, but it’s far from predictable. In fact, as a composite boardwalk heats up in the sunlight and the outer plastic begins to get disfigured, the inner wood flour core of the composite boards can start to shift around in erratic ways. Because it lacks grain, there’s no way to know which way the wood will move. The result can be a warped, wobbly mess of swollen boards that won’t stand the test of time.
3. Composite Decking Materials are Susceptible to Scratches
Whether it’s made of commonly used polyethylene or the more durable polypropylene, the outer surface of composite decking material is notoriously thin. This means it can easily become scratched. When scratches occur, moisture can seep down into the inner layers and cause water damage. This flimsiness doesn’t make sense for a large, high traffic area that will be constantly exposed to the elements. The surface of composite decking is so delicate that manufacturers even recommend only using plastic snow shovels to clear away snow and ice! How exactly would that work for a large city boardwalk? It’s just not practical.
4. Composite Decking Materials are Vulnerable to Mold and Decay
The same thin plastic outer layer that makes composite decking materials susceptible to scratching can leave it exposed to incurring other types of damage as well. Once that surface layer is breached, the water and other substances that penetrate through to the core of the planks can cause mold and decay. Because the cores include finely-ground wood flour rather than actual planks of natural wood, the wood elements have been stripped of their natural weather-resistant resins. This makes them extremely prone to weather damage. In fact, each plank’s surface is automatically breached upon installation when it’s punctured with screws. So much for durability!
This article has demonstrated some of the weaknesses of composite decking. The last installment of this three-part series will explain how the so-called “eco-friendly” material is actually not such a green choice after all.