Composite Decking Problems and Boardwalks

It seems that every year another boardwalk is being replaced. Whether the catalyst is a hurricane or just age, these monstrous projects keep coming up. When “boardwalk season” comes around, new construction bids and RFQs are on everyone’s minds.  Unfortunately, pressure is being brought to bear on city planners from environmental lobby groups to use composite decking to rebuild the boardwalks.  I’m not going to try and pretend I’m unbiased in this ongoing fight between tropical decking and composite decking.  Working for a lumber company, I obviously have already firmly announced my opinions on which is the better product.  But I hope to be able to lay out some serious concerns about using a composite decking product (regardless of manufacturer) in a boardwalk application.  In the end, I think you will see that the best choice is natural wood, probably something like Cumaru or Ipe.

Wood vs Composite Decking

Mediocre Hardness

Ipe and Cumaru decking are almost 10 times harder than composite products.  While this medium hardness may be fine for your backyard where a couple people walk across it daily, imagine the damage wrought by hundreds of thousands of people walking across a boardwalk each day.  As we will see in the points below, damaging the outer core of composite decking can be catastrophic, and this lower hardness practically ensures that damage will occur in such high traffic conditions.

Heat Build up

Composite Decking is essentially plastic.  Some manufacturers use an outer shell of pure polyethylene (the same stuff used in water bottles), while others blend the plastic in with the wood flour (ground up wood product).  Plastic is notorious for retaining heat and getting very hot in direct sunlight.  Again, while this may be fine in your shaded or partially shaded backyard, a seaside boardwalk is in direct sunlight all day long.  I wouldn’t recommend walking barefoot on any boardwalk for many reasons, but it happens.  At least once anyway.  Once you burn your feet, you probably won’t do it again. 

In addition to the discomfort factor, when plastic heats up, it breaks down.  Some variants will exude their oils, some will let off gas byproducts, but all of them will weaken over time.  Suddenly your boardwalk is very hot, and it smells like… well, burned plastic. 

Plastic also retains its heat longer, and even after the sun goes down, the boardwalk will still be hot, and that plastic will continue to break down.  This constant bombardment day in and day out will result in a boardwalk that needs to be replaced rather quickly.

Slippery

What is plastic?  It is an oil based product.  Oil and water do not mix, and when this is attempted, you get a very slippery surface.  Most composite manufacturers have attempted to fix this by adding texture and faux wood grain, and in many cases, they have had some success.  But look at your average boardwalk.  As stated above, the heat build up will degrade the plastic and even cause it to weep oil.  The boardwalk is by the ocean, so it is constantly exposed to water.  Now add in ketchup, mustard, cotton candy, funnel cake, deep fryer oil, suntan lotion, surf wax, and all other manner of stuff that will inevitably be spilled or dropped onto the plastic surface.  Imagine the army of lawyers ready to represent the tourist who slips and falls on your city’s boardwalk.

Non-Biodegradable

While we are on the topic of replacing the boardwalk, what happens to this composite lumber when it is torn up and carted off?  Composite manufacturers and environmental groups tout the “green” nature of composite decking, yet the one place where this material will be guaranteed to last a lifetime is in the landfills. 

Secondly, and even more importantly, is what will happen when another storm hits the boardwalk and washes this non degrading material out into the ocean?  God forbid another storm like Sandy hits, but I’m sorry to say that it will happen one day.  Unless the normal weather patterns shift significantly (and we are in real trouble if that happens), the east coast of the US will always be hurricane alley.  We can count on storm damage washing boardwalks or parts of them out to sea, where those non degrading pieces will sink to the bottom and remain there for thousands of years, or wash ashore somewhere else and be moved to a landfill where those pieces will sit for thousands of years.  Even the most hardy of exterior woods like Ipe, however, will degrade completely in a landfill or in the ocean in about 10 years.

Not Weather and Mold Resistant

This may be the most shocking element of composite decking that people don’t usually realize.  The original composites were homogenous mixes of wood flour and polyethylene or PVC extruded into boards.  These quickly fell out of favor (mostly due to class action lawsuits), because wood flour is still wood, and it will absorb moisture very quickly despite the plastic binders. 

Real wood contains complex structures that absorb and shed water and nutrients that feed the tree. Natural resins protect against insects and mold.  Wood flour is basically wood ground very fine, thus eliminating all the natural resins and cellular structure that defeats insects and mold.  The cellulose that is left over in wood flour is like candy to mold, since it is already broken down into simple sugar form. 

Later “advancements” encased this wood flour core with pure plastic “cap stock,” thus blocking out all these harmful factors from the vulnerable inner core.  This, however, produces a bigger issue now that there is a heterogeneous construction that reacts differently to heating and cooling and daily wear and tear.  This process can crack the shell or cause it to separate from the core, thus compromising the strength and weather resistance.  If the thin cap stock is punctured, the inner core is exposed to the elements where mold and decay can take hold.  Just the act of installing the decking will puncture this, as the boards are screwed down or cut to length exposing the core.

Not Scratch Resistant

Some of this relates back to the medium hardness, but essentially, polyethylene is a weak plastic; polypropylene, though rarely used, is much tougher. Regardless of the type of plastic being used, the cap stock style decking relies upon this water resistant outer shell to weather and mold proof the inner wood flour core.  However, like cheaply made plywood, this shell is extremely thin and easily scratched, thus exposing the water and mold loving inner core. 

Most composite manufacturers, in fact, warn you not to use a metal snow shovel to clear the deck.  In a larger boardwalk situation where the city plows the boardwalk just like they would the roads, you can imagine what damage a truck plow would do to it.  Even if an army of city workers armed with snow shovels is used, are they really only going to use plastic shovels in a wet and icy environment?

Not Renewable

Polyethylene, polypropylene, and poly vinyl chloride do not grow on trees.  These are petroleum products that rely upon one of the most environmentally unfriendly industries around.  The entire composite decking industry was actually started by the Oil companies who were mandated to find a use for the massive amount of harmful byproducts produced in their manufacturing process.  So while at least this waste is being put to use, it is still reliant upon heavy industry to produce it in the first place.  Most composite manufacturers claim a certain percentage of recycled products, and I have no doubt this is true.  As I have shown above, we are still talking about a non degradable material that will need to be replaced and eventually end up in a land fill.  How is that green? 

Ipe, Cumaru, Redwood, etc does grow on trees, however.  The myths of the lumber industry deforestation are just not true, and heavy regulation and forestry management is planting 10-20 trees per each one cut down.  These grow back and are constantly renewable, let alone the key role that trees plays in our environment.  The entire lumber industry makes up about 2-3% of deforestation in reality.  How many oil companies do you know of that put oil back into the ground?

Not Fire Rated

Ipe has a class A fire rating which makes it very difficult to burn.  Composite decking does not, and in fact, when the plastic melts, it releases very toxic gases.  In the backyard, where you might occasionally drop a charcoal briquet, this doesn’t sound like a big deal.  Now look at a boardwalk where hundreds of restaurants and street vendors work with open flames, grills, burners, deep fryers, etc.  Imagine the catastrophe when a fire breaks out, and the decking begins to melt.  Even if it isn’t a total loss, some boards will deform from the heat and need to be replaced.  The removed boards then have to be disposed of, and we go back to the environmental issues mentioned above.

Not as Strong

Strength of the composite materials will vary from manufacture to manufacture, but the fine print of most installation manuals will recommend you install the decking boards on 12″ on center joists. The typical 16″ center can be done, but bounce and deformation is more likely.  Most plastic has a “memory” too, and once it is deformed, it won’t spring back.  The wood flour core is not very strong and relies upon the outer plastic shell to stiffen it.  If this shell is compromised in any way, the strength will fall off considerably.  Now, release the summertime throng of traffic on the boardwalk and imagine how that bounce and deformation quotient will climb exponentially.  So you install the composite on 12″ centers.  Imagine the additional cost of the structure over the entire span of an average beach community boardwalk!

Unpredictable Movement

While we are on the subject of deformation of the boards, let’s look at movement.  Composite decking manufacturers tout how stable their products are and how superior they are to wood because of this.  Wood moves, we all know that.  But we also know how and why it moves.  Wood will move across the grain and almost not at all along the grain.  We can even predict how much it will move, and we have hundreds of years of experience building around that movement. 

Plastic, however, also moves, and it moves in a big way when heated as stated above.  The inner wood flour core also moves, because it is wood.  However, without the structure of natural wood, there is no grain, so it will expand across and along the boards.  Add the plastic outer shell, and now it only expands.  That plastic shell is stretched as the core moves, but it won’t snap back as the wood flour shrinks again.  Now you have a core that can separate from the shell, and you have uneven warping along the length of the board, especially since the ends that were sawn to length have exposed cores that will swell even more than the interiors. 

Boardwalks are wide structures, and end to end butt joints have to happen to span the entire width.  Now you have swelling on both ends of the boardwalk as well as each of those joints in the middle.  If the boards are staggered, as is common in construction, you end up with swelling and moisture and mold traps spaced sporadically all over your boardwalk.  This sounds like a recipe for disaster that will need to be replaced quickly, thus sending all this composite material into the landfill.  See points 3 and 6 above.

Composite Decking Problems for the Boardwalk

I’ll be honest, when I started outlining this article I came up with 20 points within 10 minutes.  I’m not even mentioning the aesthetic reasons for not using composites.  Who has nostalgic childhood memories of strolling along the plastic boardwalk?  I didn’t even mention the price either.  In every case you will find that composites are equal to or more expensive than Ipe, which is considered to be the most expensive decking option on the market.

I think price and aesthetics are important, but let’s get real: the probability that this boardwalk will need to be replaced within 5 years, if by no other reason than storm damage, leads to the environmental impact.  I hear about the green nature of composite decking all the time.  The funny thing is that none of the manufacturers are calling it a green product anymore.  20 years ago it was the call to arms, but lawsuit after lawsuit has changed their tune.

So City Planers and contractors, the next time you are approached by the Sierra Club or Greenpeace, and they threaten to put an injunction against you if you use natural wood, ask them how they can in good conscience support a composite product that isn’t renewable, relies on non-green industries to produce waste, and will not biodegrade.