With factories running 24 hours a day to meet demand, makers of plastic-based building materials such as decking, fencing, and siding are moving into the mainstream at warp speed. Are these products the answer to our durability woes, or merely a fresh face shaking up an old business?

There's a scent of melting plastic wafting through the corridors of many a U.S. laboratory these days, as entrepreneurs--big and small--chase the perfect formula for the next generation of high-tech building products. In this shiny new fantasy of yestermorrow, two of America's favorite by-products--wood and plastic--have come together in super-durable decking, fencing, siding, roofing, and even framing.

The hype is not far from becoming reality. Freedonia Group, a research firm in Cleveland, just finished a study on plastic-wood composite lumber. It predicts that "demand for composite and plastic lumber in the residential construction market will expand by 12 percent every year through 2006." The lion's share of that growth will happen in decking and other outdoor materials, but manufacturers such as Andersen and Boise have already introduced other plastic-based products that are poised to challenge long-held market sectors.

James Morton, a partner with Exton, Pa.-based Principia, another building product research and consulting firm, has also tracked the plastics industry for several years. He says the plastics marketplace has now entered a period of intense competition--due in large part to the success of companies such as Winchester, Va.-based Trex, the dominant wood-plastic decking maker. "They have been putting the stuff down for 10 years now," he says, "and now they're competing in a brand war."

"Ultimately," he continues, "it's going to come down to who has the best brand, plus the strongest market areas and distribution. The reality is that most lumberyards will only stock two or three brands of [plastic-wood] products. The Home Depot and Lowe's are out there saying, 'Just give me the big ticket item.' They may not necessarily even be making money on these products, but they're making plenty on the square-foot sell-through of fasteners and accessories."

Cleverness vs. clout

Polyethylene-wood decking by Trex
Courtesy Trex Polyethylene-wood decking by Trex

But despite the fact that seven companies--Trex, Marley Mouldings, Royal Group, U.S. Plastic Lumber, CertainTeed, Andersen, and Fypon--account for almost 45 percent of the U.S. plastic and wood-plastic composite market, some smaller companies feel they can easily hold their own.

For example, CorrectDeck, a wood-plastic composite decking manufacturer based in Biddeford, Maine, currently serves the East Coast to Virginia, some of California, and part of the Midwest, plus England and Japan. Gary Weinstein, the company marketing director, says times are "very, very good," and shrugs off the threat of giant conglomerates edging his firm out of the market.

"This industry is an art, not just a science," says Weinstein. "At best, it's only 15 years old, and for only two or three years have these products been fully accepted as a legitimate replacement for cedar or other [premium] decking.

"Trex is a good product," Weinstein adds, "and they've done a good job creating a market--but they've got a 15-year head start, and they still don't offer wood graining. We also have a hidden fastener system."

Those two features, he says, have propelled CorrectDeck's rapid growth. But the company's biggest test may involve its distribution channels and processes. Ordering a color that is not in stock at the lumberyard, for example, can result in a special order cost of 30 percent.

"All of the material leaves the plant at the same price," notes Weinstein. "So those markups are not in our control."

The magic mix

Perhaps the biggest technical challenge in creating plastic-based building materials has been finding just the right mix of plastic and fibrous ingredients. They need to resist the sun, retain their color, stay hard, and repel moisture--a tall order. Plastics used by different manufacturers have very different qualities. Some use only polyethylene (PE). Others prefer to use polyvinyl chloride (PVC) or polypropylene (PP). And the ratio and type of fiber used varies, from wood flour to maple fibers to fiberglass.

Polypropylene-wood decking by CorrectDeck
Courtesy CorrectDeck Polypropylene-wood decking by CorrectDeck

Producers of plastic-fiberglass composites, such as Tony Nolo of American Composite Timbers in Spring Lake, N.J., thumb their noses at the use of wood fibers, suggesting that they absorb water and make wood-plastic exterior products inappropriate for very wet areas (such as boat docks) or very humid climates.

"Wood-based products are great if you live in a dry climate," Nolo contends, "but not for wet areas like Florida."

There is some evidence that wood-based plastic composites can degrade under severe conditions (see "Durability" sidebars, below), but such decay is typically minimal and highly contingent on the specific formulation.

"The product has been around long enough now that if there were any sort of serious problem, I would have heard about it," says Morton.

Some plastic products contain no fiber at all. For example, U.S. Plastic Lumber (USPL), based in Boca Raton, Fla., offers unreinforced high-density polyethylene (HDPE) decking made from 90 percent recycled polyethylene, plus additives. These all-plastic products avoid the wood fiber vulnerability issue altogether, and they typically hit the market with longer warranties--up to 50 years.

So why haven't more manufacturers gone over to all-plastic products? That depends on whom you ask.

"Using wood fiber makes the product much stiffer," according to CorrectDeck's Weinstein. Trex offers its own list of reasons for composite decking's superiority. It suggests that pure plastic products don't take paint well--so they can't be restained like some wood-plastic composite (WPC) products--and that without the wood fiber, they become more slippery when wet. Of course, the latter criticism depends somewhat on surface texturing.

Carefree Xteriors Structural Lumber by U.S. Plastic Lumber
Courtesy U.S. Plastic Lumber Carefree Xteriors Structural Lumber by U.S. Plastic Lumber

The technical specifications for USPL's unreinforced product do suggest that it has less flexural strength than a fiber-containing version. It also comes in only light colors. On the other hand, the product absorbs almost no moisture, making it well suited for extremely damp conditions.

But Nolo asserts that the main reason wood has been the admixture of choice is more about economics than engineering: Big lumber companies create huge amounts of wood waste and need to get rid of it somehow.

Nobody's denying the benefits of using their own waste stream. Andersen, for example, has developed engineered decking and Renewal windows (see product blurb, below) from Fibrex, a wood-PVC composite made from materials reclaimed at its window plants. CorrectDeck relies largely on shavings from maple wood flooring manufacturers for its wood fiber.

Shades of green

This year Trex decking won the Virginia Governor's Environmental Award for the second time. The product has earned gallons of good ink for its positive impact on the environment, primarily because its plastic component (50 percent of the finished product) comes from recycled grocery bags and pallet wrap--keeping these materials out of landfills.

But WPC products have earned their green reputation more by default than by design. Few in the industry describe themselves as environmentalists. Instead, big companies see the use of their own waste by-products as a shrewd business decision that happens to spare landfills from tons of material.

And for those who don't use a high percentage of recycled plastics, the green argument leans on durability--longer life span equals lower environmental impact overall. For example, in its 40 percent polypropylene (60 percent sawdust) decking, CorrectDeck uses about half virgin plastic and the other half (20 percent) recycled.

"The markets for virgin and reclaimed plastics are both very volatile," Weinstein notes. "Because we use polypropylene, our product is a lot stiffer [than products of competitors who use polyethylene]. Also, the mechanical properties of reclaimed stuff can be all over the map."

Andersen uses reclaimed PVC in its Renewal windows for obvious reasons: It's one of the major scrap materials from its vinyl window operations (the other being wood).

Virgin PVC, on the other hand, with its controversial environmental record, hasn't yet become one of the mainstays of plastic-wood composites. That could change, says Morton, but the real driver of the industry at this point is waste reduction, which makes recycled materials the first choice.

New contenders

Disciples of the plastic revolution believe this new industry is just getting started.

"There are some very exciting things happening in siding, for example," says Morton, referring to Boise's HomePlate product. This is the first wood-plastic siding material to be offered commercially. While it's not technically a composite, because it isn't extruded, the materials are the same--HDPE and reclaimed wood fiber.

"We're very competitive with fiber cement in our on-the-wall cost," says Mike Moser, building solutions communications manager for Boise. "We have less waste, and it's easier to back cut and notch." He says the reason other WPC makers haven't offered siding is technological.

"We had to re-engineer the molecular structure of the material so primer would adhere to the substrate," he explains. "It's going to take them awhile to develop some of this technology." Like fiber cement, the product must be painted, but Moser says Boise isn't yet "giving a number" on how long paint will last, because the product is so new.

BUILDER magazine

Roofing made with plastics is also being explored. Teel Global Resource Technologies in Baraboo, Wis., has developed a polyethylene-wood (and jute) fiber composite roofing material called Panelshake that comes with a 50-year warranty. The company expects to roll out the product commercially in a few months.

Another quiet movement in the WPC industry is the move toward structure. Plastic enthusiasts would like to replace that sacred cow of residential construction--wood framing--with structural WPC products. To date, the only structural plastic-based materials available have relied on fiberglass, not wood fiber. They're frequently used in commercial infrastructure. And critics of wood-mixed plastics, such as Nolo, say WPC makers simply cannot compete on cost with the makers of engineered wood products. He says that the cost of adding sufficient fire retardant to the mix, for example, would push the price through the roof.

But Morton and other industry watchers see nothing but growth ahead for residential WPC products.

"Many in the business are now realizing the next step is to offer more structural [plastic-composite] systems. I hear many clients who believe it's possible we could see cost-effective structural parts in three to five years."

A report at the annual meeting of the Plastic Lumber Trade Association last year confirmed that "several companies have been working on structural lumber systems."

In the meantime, says Ken Rhodes, senior staff engineer at Underwriters Laboratories in Norfolk, Ill., "an awful lot of our clients are getting into this material."

Durability: Will it Rot? Although life-cycle testing is still needed, lab simulations show that properly formulated wood-plastic composites resist fungal decay.

Several scientists last year published a study on the durability of wood-plastic composites (WPCs) made with high- density polyethylene (HDPE). They found that products with a higher HDPE-to-wood-fiber ratio showed less weight loss in material exposed to fungi. They noted, however, that adding 2 percent zinc borate to the mix prevented any weight loss, and accelerated leachate tests suggest that the borate will hang around for 20 years.

Decay in general was minimal in all the WPC products tested. The researchers did note, however, that "as the level of wood content increased, the level of weight loss increased."

Another study in 1996 corroborates the more recent one. Graduate research at the University of Toronto found that WPC products with wood content higher than 60 percent demonstrated much greater fungal decay and loss of flexural strength.

It should be noted that in the first study, WPCs outperformed ordinary, unprotected wood exposed to the same conditions.

Sources: "Durability of an Extruded HDPE/Wood Composite," Forest Products Journal, Vol. 52, June 2002; "Effects of Extreme Environmental Conditions and Fungal Exposure on the Properties of Wood-plastic," by Behrouz Naghipour, University of Toronto, 1996

Durability: Will it Wick? "These products really don't absorb much water," notes Ken Rhodes, a senior staff engineer with Underwriters Laboratories in Norfolk, Ill. "We're testing a [WPC] product now, and we'll run it through various environmental conditions and flexural strength testing."

Trex, for example, underwent similar testing. In long-term water immersion tests, a 36-inch piece of Trex kept underwater for 24 hours varies in width by plus or minus 3 percent, and a piece kept in high constant humidity varies in width by 1 percent. After 24 hours underwater the sanded-surface product absorbs about 4.3 percent of the water, and the company's unsanded product fares better, at 1.7 percent absorption.

Durability: Will it Melt or Warp? The thermoplastics used in WPCs are chosen for their fairly low melting point (below 392 degrees F, according to the Forest Products Journal), because the wood with which they're mixed has "limited thermal stability." As part of ASTM testing, the products must perform adequately in the kind of heat you might encounter in direct sunlight in a Southern climate. While some softening is often noticeable as the material warms, WPCs typically retain most of their flex strength well above summer's worst. Andersen's Fibrex, for example, has tested well at up to 203 degrees F.

Learn more about markets featured in this article: Winchester, VA, Virginia Beach, VA.