Industry News
What’s In This Stuff? – Composite and PVC Decking
6 years ago Posted in: Industry News 0

Not all composites and PVC decking and trim are alike. Here’s why–and how to pick the best products for your store.

By Craig Webb, Pro Sales Magazine 6/10/2011

Tell dealers a species or grade of wood and, more likely than not, they can envision exactly what you’re talking about and detail its qualities. But then try asking them to explain what makes one brand’s wood-plastic composite (WPC) or polyvinyl chloride (PVC) decking or trim different from another. A lot of them will be stumped.

Arguably, no other product in a lumberyard matters so much financially to dealers and yet is so little understood as composites and PVC. At the same time, it’s likely that no class of products has grown up so fast. The $1.1 billion composite and PVC decking and railing industry still is in its teens. And like many teenagers, it’s a gangly mix of impressive achievements and dumb errors, a body on which onlookers project a lifetime of achievement based on a scant history of actual performance.

Similarly, PVC trim is expected by 2014 to surpass metal as the No. 2 material used. And while its performance also has improved in the past decade, it still struggles to beat problems caused by thermal expansion, not to mention holding prices in an unsettled raw materials market.

Manufacturers’ past claims (hyped by the press and public) that WPC and PVC were maintenance-free certainly helped confuse things, and intense competition has led producers to be intentionally vague about what’s in their products.

Should you demand to know what’s in this stuff? Well, since 2004, seven wood-plastic composite manufacturers and suppliers have faced lawsuits related to a host of problems, including fading and color changes, slippery surfaces, shrinkage, swelling, and mold. In at least two of those cases, a supplier and reseller were accused along with the manufacturer.

It takes some work, but you can learn to spot the differences between products and, hopefully, avoid future callbacks. Here’s a start.

As Much Art as Science

Creating composites and PVC often is compared to cooking, but lots of chefs would be sorely tested if they tried to whip up a deckboard or piece of trim. That’s because, unlike in a kitchen, you can’t count on the ingredients to be consistent from one day to another.

Wood and plastic typically make up roughly 85% to 95% of the ingredients’ total weight. Most of the wood consists of cast-offs from flooring factories. And except for virgin PVC flakes, all the plastic had a previous life as well. WPC and PVC manufacturers work constantly to get reliable streams of raw product, but if the wood flour has a different mix of species or the recycled plastic shipment was heavier on low-density polyethylene film, the manufacturer may need to adjust its formula.

Technology challenges are no less daunting. Consistently and accurately extruding a product–basically, cramming a hot, doughy mixture of plastic and wood through a specially shaped opening–is hard enough. Co-extrusion–pouring a syrupy plastic shell over the inner core in such a way that it bonds exactly where you want at exactly the right thickness–is an added challenge that manufacturers didn’t feel comfortable producing commercially until a few years ago.

“It’s not a highly repeatable process,” says Tom Gramlich, chief operating officer of TimberTech, which makes composite and PVC decks, porches, railing, and trim. “Every night, our operator is fighting a different set of circumstances than the night before.”

You can tell how tricky a business this is through the scrappage rate: Industry-wide, manufacturers say, roughly one-eighth of what’s produced gets rejected before it ever leaves the factory.

Production techniques also matter. For instance, take the debate over using Celuka. . It’s an option used for PVC products that gives the outside of what’s extruded an extra-hard surface. Gossen Corp. particularly likes this method when it needs to make sure the object produced meets tight specifications, such as replacement window trim. Jackson Chen of Inteplast, maker of Tufboard products and CEVN decking, shows off his Celuka products by knocking dents into trim made using the freefoam process.

Versatex president John Pace isn’t impressed, particularly since his company’s goal is to make a product that cuts and nails like wood. “You’re trying to make trim, not a brick,” he says. “To me, that (Celuka trim) isn’t wood.”

Manufacturers likewise snipe over the choices that decking producers made with their manufacturing processes. Lately, the biggest argument is over capstock–the plastic substance that has recently begun to be applied to composite decks, giving the products added protection, more intense faux-wood-grain finishes, and ever more varied color options.Capped composites are one of the hottest categories within decking, with sales rising six-fold in popularity last year, according to a new study by Principia, a research group. Meanwhile, demand for all-plastic decking rose 40% last year. Together they constitute decking’s ultra-low maintenance segment, and Principia estimates their share of the total $1.1 billion market for non-wood decking and railing has risen to 45% today from 15% in 2008.

Some firms put the capstock completely around the inner core, some skip covering where hidden fasteners go, and others leave one side untouched. All argue that these choices can result in big differences in how the products perform–stressing, of course, that their choice is what’s best. But for the most part, it’s still too early to tell which manufacturer is right.

Cost vs. Quality

What is certain is that making WPCs and PVC products requires a careful mixing of ingredients not just for performance, but for cost. One way to do that is by literally trimming away some of what’s produced. It’s a principal reason why a lot of lower-priced composite decking is flat on just one side and scalloped on the other–you use less mix to create a board.

Polyethylene and PVC today typically are made from extracts of natural gas rather than petroleum, but pricing still goes up and down with the oil market. Added cost pressures have arisen from this year’s earthquake and tsunami in Japan, which knocked some processing plants offline. You can supplement U.S. PVC production by getting it from China, but plants there make a dirty product that requires a lot of titanium dioxide to whiten it–and titanium dioxide is in short supply. Meanwhile the recession has slowed business at the flooring and cabinet shops that generate most of what becomes wood flour.

Advanced Environmental Recycling Technologies (A.E.R.T.) has found other ways to limit cost runups. It gets its plastic from recycled goods rather than virgin PVC, and over the years it has learned how to convert ever-lower grades of polyethylene into usable feedstock. (Trex also gets most of its plastic through recycling.) As for wood flour, generally the more finely ground it is, the more expensive it gets. A.E.R.T. uses relatively large flakes of wood. The result, however, is a rougher-looking board than its competitors.

But if you really want to scrimp, ultimately you need to examine your additives–the chemicals that make trim whiter, deckboards stiffer, cores less (or more) foamy, and surfaces less likely to fade in the sun or crumble. Like spices, a little additive can cost a lot. Bill Ross, vice president of sales at Fiberon, says that while wood flour can cost 10 cents a pound and virgin PVC a dollar a pound, an additive can set you back hundreds of dollars per pound.

Anatole Klyosov, a biochemist and former WPC executive, says several lawsuits this past decade involving WPCs appeared to arise from failure to use enough additives. In one case, he says, a manufacturer didn’t add enough color pigment, thus leading to fading. Another case stems from a lack of antioxidants.

“I’m astounded that we sold as many boards as we did five years ago,” one decking exec says. “Because five years ago, those boards didn’t do what they promised.”

Some manufacturers expect the number of lawsuits eventually will drop because of capstocks. Why? Think of an M&M.

Just as putting a hard candy coating around an M&M’s chocolate core protects the insides, manufacturers say pouring a cap around a WPC center protects that core from what in the past has led to its demise. “Wood fiber is the root of all problems” in WPCs, says Peter Gallagher, manager of sales development at Polyone, a leading maker of additives. It’s what in the board (that) is susceptible to bleaching from the sun, decay from the wet, and consumption from the mold, while tannins in the wood flour can get out and stain the composite.

Capstock’s advocates regularly say that adding this armor coat to the board significantly improves its long-term performance. What they bring up less often is that using capstock could make it possible to slack off a bit on what’s inside–there’s no need to put in coloring there, for instance. Whether firms actually are cheapening the insides remains an open question that likely will take years of field testing to determine.

For its part, Trex maintains that the core of its capped decking, Transcend, is exactly the same as its uncapped Accents line. “We don’t have the philosphy that you can junk up the core,” says Kyle Lancaster, Trex’s director of technical services.

Trex may be open on that issue, but it’s close-mouthed on what’s in its capstock–so private, in fact, that it won’t even say whether the capstock is animal, vegetable, or mineral. It just calls it a “shell.” You also can’t learn more about the capstock by examining a patent; like the formula for Coca-Cola, Trex’s recipe for the “shell” is a company secret.

Such secrecy is quite common among decking manufacturers. Examine Material Safety Data Sheets for most of the major WPC and PVC products in the business and you’ll find that many list up to 50% of their ingredients as “proprietary.” At least one doesn’t reveal any at all. And a lot don’t even reveal they put in any additives.(See How To Make Plastic Wood)

On the other hand, reading manufacturers’ warranties can give you a sense of what these firms believe their products can do–in contrast to the advertising claims they make. Pick up a Trex brochure for Transcend and you’ll see on the cover a boast that Transcend “Resists everything but stares.” But then go to its 25-year fade and stain warranty, and you’ll see language that makes clear its resistance is limited pretty much solely to permanent staining from food and beverage spills.

Meanwhile, TimberTech considers its warranty voided if you use a snow shovel on it. And Deceuninck’s Solstice decking, whose brochure declares it offers “The best performance under the sun,” warns that you won’t get repaid if you spill and then leave plant food on the deck or your dog makes a deposit that goes unnoticed.

Pace is amused by the trend among manufacturers to giving warranties stretching 25 years and longer on products that only came out in the Obama administration. “They make a product and throw it up on the wall and if it sticks, they market it,” he says. “Look at some of these decking products that failed. Why did they fail? There’s no long-term test data.”

Can Testing Be Trusted?

In fact, the testing protocols that companies use to justify their 25-year warranty claims are getting questioned. Historically, to estimate potential wear and tear on composites, manufacturers and academics applied the same testing standards used for treated, solid-sawn wood. But at an international conference on WPCs last month in Madison, Wis., a researcher from the federal Forest Products Laboratory said in effect that you can’t subject factory-fresh composites to those tests and get real-life results; the composites have to be “conditioned”–i.e. knocked around a bit–before being put to any tests intended to help predict a product’s long-term performance.

When it comes to creating vs. adequately testing new products, “Manufacturing went faster than science could catch up,” said one conference participant who specializes in polymer engineering. “What we’re now learning would have been nice to know 10 years ago.” New testing standards could take effect later this year.

One hoary business maxim is that a lot of competitors will pile into a new market and that, over the years, a few will rise to lead the market, a few others will hang on, and the rest will quit. The WPC decking and PVC markets appeared to be going that way, such as when CorrectDeck sold out last year to GAF. Principia says the top four players in the decking market have increased their market share from 65% in 2008 to 75% today. But lately some new players are coming in that could shake up the situation.

A notable arrival is Inteplast, which makes several private-label brands and has become the licensed producer of CEVN, a PVC decking in which each board has two colors. Meanwhile, Deceuninck made a splash at this year’s International Builder’s Show with a brand of PVC decking. And Wolf, a distributor based in York, Pa., that has expanded into New England and the Southeast, dropped AZEK’s PVC decking in 2010 to begin distributing CEVN as well as start selling its own, private-label brand of plastic deck.

How To Shop

“Saying all deckboards are the same is like saying all cars are the same,” says Gramlich of TimberTech. “A Chevette isn’t a Mercedes.”

Though virtually all industry experts agree that composite and PVC decking and trim is far better than it was just a few years ago, they stress that variations between products still run rampant. So how do you tell which product is a peach and which is a lemon? The basic answer from manufacturers is to not accept what companies say at face value and to check closely how they back up their word.

For instance, manufacturers say dealers should press suppliers to give more details about what’s in their recipes, such as what percentage of wood flour is in the total mix (over 60% should ring alarm bells), what size wood particles are used (in most cases, the smaller the better), whether the polyethylene used is low- rather than high-density (higher-density polyethylene tends to be stronger, but it’s also more expensive, and the sourcing can be spotty), and how much of a filler like talc is used (over 10% may signal cost-cutting).

Fiberon’s Ross also urges dealers to ask about the pigment used to color the product. Organic pigments will change over time, while non-reactive pigments are inert and thus will keep a color true for a longer time.

One good way to get a sense of what the manufacturer is doing is to compare its good, better, and best products. Why does the upscale version promise a longer, stronger warranty? It’s probably because it has more additives. Knowing how much more, and what extra is in there, can help you decide whether the differences are worth stocking.

Ask manufacturers what percentage of output from the production line is rejected and reground; if it’s way below 10%, the company may be intentionally permitting some less-than-optimal products to sneak through to your company’s shelves.

Likewise, ask about warranty claims and lawsuits. The volume of claims as a percent of total sales can help indicate the product’s performance. At the same time, companies that get sued over a defect are likely to have spent a lot of time making sure that problem doesn’t reoccur. How long a company has been in the business also should be taken into account.

Even after making those checks, experts agree that the only real way to be sure of a product’s quality is to install a lot of it in a lot of places and then see what happens. Frequently, that’s the first time manufacturers discover how builders’ embrace of other products can have unintended consequences for their decking and trim.

Pace says he has worried lately about whether paint companies that have made darker colors of heat-reflecting paint have spent any time seeing how that paint affects the expansion and contraction of PVC trim.

Likewise, Bob Simon of Gossen says his company got surprised when its first generation of PVC decking was placed below low-e glass. It turns out that the glass can reflect and focus the sun’s rays on a spot near the window.

“We had decks below windows and patio doors that were pretty black–getting scorched,” Simon says. “So we discontinued that whole product line, took substantial losses. That’s when we decided to change our whole process. …That’s a hard knock we went through, and some are going through that now.”

Unexpected problems are a part of the package that comes when you try to sell an ever-evolving product. Understanding how it’s made is your first step to reducing that risk.

Where To Source It

Builder magazine’s 2011 Buyers Guide lists 60 companies that make composite and PVC decking, railing, fending, and trim, and many of those firms produce goods under more than one brand name. Here’s a listing of many of the most significant companies in the game.

A.E.R.T. Moistureshield decking, railing, fencing, and trim.

Advanced Trim@right ATW trim, molding, and millwork.

Aeratis Classic and Traditions porch flooring.

AZEK Decking, porch, rail, molding, and trim.

Barrette Outdoor Living Fences and railings.

CEVN Decking.

CertainTeed EverNew decking; EverNew, Panorama, and Spectrum composite railing.

Deceuninck Solstice decking, Kodiak decking and railing.

EnduraBoard Decking and railing.

Engineered Plastic Systems Bear Board plastic lumber.

Eon: Decking, railing, and dock/marine products.

Fiberon Horizon, Outdoor Flooring, Pro-Tect, and Professional decking; Horizon Plus and Inspirations railing.

GAF DuraLife Siesta and Natural Grain decking, dock, and porch products; RailWays railing.

Geodeck: Decking and railing.

Genova Genovations decking and railing.

Gossen Passport, American Classic, and Heritage decking; Tongue & Groove porch board; WeatherReady railing.

Guardian Guardeck Prestige and Elite decking.

Inteplast TUF board decking, trim, and molding,

Kleer Trim and molding.

Koma Trim.

L.B. Plastics SheerGrain decking. SheerLine railing and fencing.

Midwest Manufacturing UltraDeck decking and fencing.

Natures Composites TerraDeck decking, TerraFence and Equine Fence fencing.

New Wood Utility boards and fencing.

Ply Gem Kroy Classic, Performance, and Elegance composite fencing, railing, and outdoor structures.

Renew Evolve deck, dock and porch products.

Rhino Rhino Deck, Rhino Vision, and Armadillo decking and railing.

Royal Group Brock Dock, Century Deck, Deck Lok, and Novation decking; Royal Outdoor Products railing; Never Rot and Royal moldings and trim.

Structure PVC Cellek decking system.

Thermal Industries Dream decking.

Tamko EverGrain decking and railing, Elements dock board, Tam-Rail railing.

Tapco IQm trim,; Foundry specialty siding.

TimberTech Earthwood Evolutions, XLM, Floorizon, ReliaBoard, TwinFinish, and DockSider decking; RadianceRail, BuilderRail and Ornamental Rail railing; FenceScape fencing; various trim brands.

Trex Transcend decking, porches, and railing; Escapes decking; Accents decking; railing brands; TrexTrim.

Universal Forest Products Latitudes Capricorn, Captiva, Intrepid, and Marine decking; Intrepid and Luster railing.

Versatex Trim and molding.

Westech Presidio decking, dock, and railing; Reliant, Sentinel, and Ultraview railing.

Notable store-label products:

The Home Depot Veranda (Various companies), WeatherBest (LP)

Lowe’s ChoiceDek (A.E.R.T. and Weyerhaeuser), Severe Weather (Fiber Composites)

Menards UltraDeck (Midwest Manufacturing)

Wolf (Wolf PVC decking and trimboards)

Intentionally Vague

Manufacturers of wood-plastic composite (WPC) and polyvinyl chloride (PVC) products closely guard their recipes for making their goods, even when they list in Material Safety Data Sheets the ingredients they use. Actually, exact percentages would be near impossible to declare because variations in core products and in the working environment can make it necessary to adjust the recipe nearly every day. But based on the collective responses, it’s a safe bet all use PVC or polyethylene, various additives, and–in the case of WPCs–wood or some other form of cellulose.
Source: Companies’ Material Safety Data Sheets

Manufacturer / Brand name(s) / Product type / What Is It? / Composition by weight
A.E.R.T. / ChoiceDek, MoistureShield / Decking / WPC / 45%-48% polyolefin, 49%-52% red oak fiber, 0.01%-1.5% carbon black (for products with colors), 1% to 5% metallic oxide pigments (for products with colors).
Advanced TrimWright / ATW Trimboard / Trim / PVC / 50%-100% PVC, zero-50% proprietary mixtures.
Aeratis / Aeratis / Porch / PVC / 50%-85% PVC compound, 10%-25% cellulose, zero to 5% lubricant mixture (calcium stearate, paraffin wax, polyethylene wax), zero to 3% process aids, acrylic polymers (proprietary), zero to 10% impact modifiers, acrylic (proprietary), unlisted amount of colorants (titanium dioxide and proprietary organic and inorganic pigments).
AZEK (Vycom Corp.) / PVC, Vintec I, Vintec II, Celtec, AZEK / Trim / PVC / 70%-95% PVC polymer, zero to 30% calcium carbonate and titanium dioxide, zero to 2% heat stabilizer (organotin compounds), zero to 4% lubricants (calcium stearate, paraffin, polyethylene, polyamide compounds, or esters); zero to 2% process aids (acrylic compounds), zero to 10% impact modifiers (CPE, ABS, MBS or acrylic compounds), zero to 2% organic and inorganic colorants, zero to 1% blowing agents (azo compounds or sodium bicarbonate).
Barrette / Barrette Outdoor Living / Railing, fencing and sheds / PVC / “All ingredients are bound up in the manufacturing process and are not expected to create any hazard in handling or use. Finished goods are inert.”
Deceuninck North America / Composite wood product / Decking / WPC / 55%-90% wood flour, 5%-35% high-density polyethylene, <10% inert proprietary ingredients, >5% talc.
Deceuninck North America / PVC compound / Decking / PVC / >30% PVC resin, <5% organotin stabilizer, <70% mixture of proprietary additives.
Fiber Composites LLC / CertainTeed EverNew PT / Decking / WPC / “This matrix contains predominantly wood fiber and polyethylene. The polyethylene can be sourced as virgin or regrind (recycled) materials. The standard product is approximately 50% thermoplastic and 50% wood fiber.”
Fiberon / Fiberon decking including Home Select; Horizon and Pro-Tect decking / Decking / WPC / 40%-60% wood fiber, 60%-40% polyethylene.
Fiberon / Horizon Plus / Guardrail / WPC / “This mixture contains predomantly wood fiber and PVC. The PVC can be sourced as virgin or regrind (recycled) materials). The standard product is approximately 75%-90% thermoplastic and 10%-25% wood fiber. In addition, the extruded profile (guardrail components) are covered in a predominately PVC capstock.”
Fiberon / Outdoor Flooring / Decking / PVC / 75%-99% PVC resins, zero to 20% calcium carbonate, zero to 12% titanium dioxide, zero to 10% impact modifier, zero to 7% wax, zero to 5% processing aid, zero to 2% calcium stearate, zero to 2% tin stabilizer, zero to 0.5% pigment.
Formosa Plastics Corp. / CertainTeed EverNew LT / Decking / PVC / 75%-99% PVC resins, zero to 20% calcium carbonate, zero to 12% titanium dioxide, zero to 10% impact modifier, zero to 7% wax, zero to 5% “processing aid,” zero to 2% calcium stearate, zero to 2% tin stabilizer, zero to 0.5% pigment.
GAF / DuraLife Natural Grain Collection / Decking / High-density polyethylene/rice hull / 40%-60% rice hulls, 25%-50% polyethylene, 10%-35% proprietary non-hazardous materials.
GAF / DuraLife Porch Collection / Porch / WPC / Zero to 70% sawdust, 25%-50% polypropylene, 15%-35% talc, 1%-5% zinc stearate, 10%-35% proprietary non-hazardous materials.
GAF / DuraLife RailWays / Railing / PVC/rice hull / 40%-60% rice hulls, 40%-60% PVC, zero to 5% calcium stearate, zero to 5% carbon black, zero to 5% calcium carbonate, zero to 5% titanium dioxide, zero to 5% crystalline silica, zero to 5% amorphous silica.
GAF / Duralife Siesta / Decking / Composite with wood or rice hulls / Zero to 70% sawdust or rice hulls, 25%-50% polypropylene,
15%-35% talc,10%-35% proprietary materials.
Guardian / Guardeck Elite / Decking / PVC / 50%-100% PVC, zero to 50% proprietary.
Guardian / Guardeck Prestige / Decking / WPC / 50%-65% wood flour, 30%-50% recycled high-density polyethylene flake, 1%-4% coloring agents, 1%-5% polyethylene homopolymer, zero to 8% proprietary mixture.
Inteplast Group / Tuf board products, Veranda HP, CEVN decking, InteFoam, InteCel, InteCel PW / Decking, trim, railing, fencing, molding, millwork / PVC / 50%-100% PVC, zero to 50% “proprietary.”
Kleer / Kleer Decking / Trim and molding / PVC / >70% PVC, <20% calcium carbonate, <15% titanium dioxide, <9% proprietary.
Natures Composites / TerraDeck / Decking / Polyethylene/wheat straw / 60% wheat straw, 30%-40% polyethylene,<5% proprietary.
Rhino / Master Rhino Deck / Decking / WPC / 30%-50% virgin high-density polyethylene, 50%-65% wood flour, 1%-4% colorant, 1% to 4% UV treatment (carbon black and titanium dioxide), zero to 8% proprietary mixture.
Tamko / EverGrain / Decking / WPC / 40%-60% polyethylene, 40%-60% wood fiber dust, zero to 5% coloring agent.
TimberTech / CX-9 / Decking / WPC / 40%-60% wood fiber dust, 25%-60% HDPE, 5%-20% “trade secret,” and another 2%-10% “trade secret.”
TimberTech / XLM / Decking / PVC / 65%-90% PVC, 3%-15% inert fillers (calcium carbonate, titanium dioxide), 1%-5% proprietary heat stabilizers, 1%-5% proprietary lubricants, 1%-5% proprietary process aids, 2%-10% proprietary impact modifiers, 0.1%-7% proprietary pigments.
Trex / Accents / Decking / WPC / “Plastic obtained primarily from reclaimed/recycled grocery bags and stretch film; wood fiber is typically obtained from furniture makers and/or waste pallets. Standard product is approximately 30%-60% thermoplastic and 30%-60% wood fiber.”
Trex / Escapes / Decking / PVC / <90% PVC, <10% acrylic copolymers, <7% calcium carbonate, <7% glass fiber, <4% calcium stearate, <3% paraffin wax, <12% titanium dioxide, <2% organotin (SN) complex, <4% brown pigment (titanium, chromium, antinomy), <2% organic calcium compound, <2% chromium compound, <4% brown pigment (Cr, Sb, MN) compound, <10% talc.
Trex / Wood-polymer products, including Transcend / Decking / WPC / “Plastic obtained primarily from reclaimed/recycled grocery bags and stretch film; wood fiber is typically obtained from furniture makers and/or waste pallets. Standard product is approximately 40%-50% thermoplastic and 50%-60% wood fiber.”
Universal Forest Products / Latitudes (listed in MSDS as “Extruded Wood Plastic Composite Products” / Decking and railing / WPC / 50%-75% wood flour, 25%-50% high-density polyethylene, <10% talc, <10% inert proprietary ingredients.
Versatex (Wolfpac Technologies) / Versatex Trimboard / Trim / PVC / >70% PVC, <10% calcium carbonate, <20% titanium dioxide, <20% proprietary additives.
Wolf / Wolf PVC Trim / Trim / PVC / 50%-100% PVC, zero to 50% proprietary mixture.

How To Make Plastic Wood

Creating a consistent product isn’t easy when the ingredients are changing daily.

Making wood-plastic composite (WPC) and polyvinyl chloride (PVC) products is a lot like cooking barbecue: It’s mainly about meat and heat, but arguments rage over what’s the best combination of core ingredients, spices, and techniques. It’s much the same here: Recipes are closely guarded secrets, and you can’t even visit some factories. But all share some basic principles.

The core ingredient for both WPCs and PVC products is plastic. Typically it’s one of two things. The first is virgin PVC, a byproduct of the refining of oil and natural gas. The second is polyethylene. It’s created by recycling just about any plastic product you can imagine: shrink wrap, plastic shopping bags, soda bottles, even the nearly invisible film that’s put on Styrofoam cups at your favorite fast-food place and used to imprint an ad. This recycled plastic gets cleaned and processed into granules the size of short-grain rice. Companies also use plastic from factory rejects that were reground.

Wood (or a cellulose equivalent, such as rice hulls or wheat straw) provides the other major component of WPCs. It’s ground into what’s known as flour–particles so small that you can put 100 in a line and not cover an inch. Technically, any type of wood can be used in WPCs, but manufacturers prefer hardwoods over softwoods and look for woods free of tannins (e.g., maple rather than oak). Some of the first WPC was made from ground-up pallets. Today, companies that specialize in wood flour procure their raw material from flooring factories, furniture makers, and cabinet shops; they only go direct to the forest as a last resort. Because sourcing companies use varying species of wood, and because wood harvested at different times of year has different qualities, WPC deck firms constantly have to test the raw materials and adjust their recipes.

Then come the additives. They include stabilizers (which help the material mix together), waxes and lubricants (they help the product move smoothly through the extruder), stiffening agents (keep the end product from acting like wet spaghetti), impact modifiers (reduce brittleness), “blowing agents” (cut heat levels caused by the extruder and help the product expand), and colorants. PVC but not WPC gets titanium dioxide, which removes color and is what makes PVC trim so white. You can make WPCs and PVCs without additives, but the process would be hard and the end product pretty ugly.

1-Prepare and Mix Ingredients

The wood flour used in WPCs has to contain far less moisture than one would find in nature, so before going into the hopper, it gets heated and dried until it’s almost free of water. At the same time, the plastic–which looks like soap flakes–is heated to a liquid state. (That’s why it’s typically called “resin.”) Those ingredients are mixed along with additives until the plastic is considered to have thoroughly covered (or “encapsulated”) the wood flour. If you’re making PVC products, there’s no wood flour used, so only plastics and additives get mixed. Ingredients for a top coat, or capstock, on WPCs are mixed separately. Capstocks don’t have wood flour, but exactly what each company puts in is a closely guarded secret. Basically, it’s a plastic with additives like colorants.

2-Extrude the Mixture

The heated mix is pushed through a die that typically contains a series of four to eight computer-cut metal plates. These progressively shape the product into the desired configuration: a deck, a piece of trim, a railing component. The capstock mixture gets introduced into the die near the final plates, after the core’s shape has been formed. WPCs and PVCs get bigger as they leave the die. This expansion is known as freefoaming. At this point, some manufacturers move the extruded product immediately into a vacuum chamber. That process keeps the freefoam expansion from taking place and instead yields a hard crust on the surface and softer material inside. This Celuka process is often used to produce products that have to meet tight standards on size variations.

3-Cool What’s Produced

The extruded product has the right shape but is still so hot it’s barely stiffer than a licorice whip. Stiffness comes as the product cools. Most manufacturers do this by spraying water on the product as it’s pulled down the line, but it’s a fine art; a misdirected spray can cause unreached sections to bulge. At least one manufacturer cools its decking with air alone, sending the product on a circuitous trip up and down several adjacent lanes, like going through an airport security line. Another applies giant cooling wheels to each side of the product. By this point, manufacturers have a good idea of how the end product will look. Often they’re unhappy; it’s not unusual to reject as much as one-eighth of the output. The discards are set aside to be reground and put back into the mix.

4-Imprint, Treat, Cut, Stack

By now, the product has cooled to the point where its surface can get imprinted with a faux-wood finish. Typically this is applied with a big wheel that contains a grain pattern. Depending on the manufacturer, this pattern can be set up to repeat after so many feet or–by moving the board left or right under a wide wheel–can make the grain on one board in a pallet nearly unique from others. Here also is where manufacturers apply more additives, particularly those designed to keep the product from fading when it is put out in the sun. After that, the product is reinspected, cut to desired length, and stacked. Often it’s still warm. Problems have been known to crop up if it hasn’t been given time to completely cool before it’s put on a truck and heads out the door to you.

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