Gardeners are usually the first to praise the natural and authentic, and the first to avoid anything "plastic." But when it comes to using wood in the garden, they face a conflict: whether to use rare or exotic trees that are naturally rot-resistant, or turn to less-resistant wood treated with potentially toxic chemicals to prolong its useful life. There is a third way: substitute woodlike plastic materials for the real thing. These "woods" score points environmentally because they resist decay and rot, and are made entirely of recycled matter. They've come a long way in both looks and performance, and now that structural load-bearing components are also available, low-maintenance and long-lasting decks, walkways, boardwalks, arbors, raised beds, and other outdoor structures can now be built entirely from these materials.
Compared to wood, lumbers of recycled plastic will never need staining or sealing, and they never produce splinters. Long plank lengths that allow seamless decks are often available. Plastic decks typically cost slightly more than wood ones, but if you consider the lower cost of maintenance (periodic staining and sealing), the lifetime costs of plastic lumber will be a lot lower than for wood.
Recycled-plastic lumber first became available in the 1980s. Unlike most new products, its development was driven not so much by end-use needs, but rather by the need to deal with the growing mountains of plastic in landfills: 19 million tons a year, more than 120 pounds per person! Throughout the 1970s and '80s, solid-waste officials came to recognize that for recycling efforts to succeed, a market for recycled products would have to be created.
Government agencies and the plastics industry have invested millions of dollars researching how to utilize discarded plastic. Producing "lumber" from recycled plastic seemed like a great option: it used a lot of waste plastic, and created a weather-resistant product with many applications around our homes, parks, and businesses. By 1995, about 1 million tons of plastic were recycled in the United States, according to EPA figures.
These products are manufactured from various combinations of plastic and other materials.
Recycled plastic only. In North America, about 30 manufacturers currently produce lumber products out of 100 percent recycled plastic. Most of these companies use only high-density polyethylene (HDPE)--the stuff of milk jugs and some grocery bags--though some producers still use commingled plastic. The past several years have seen considerable consolidation among manufacturers. U.S. Plastic Lumber Company Ltd., a publicly traded company based in Chicago, has bought up nearly a dozen other manufacturers and is now the largest of these companies. One of their products is Carefree Decking.
Using just HDPE, manufacturers of recycled plastic lumber are able to control their products' structural properties. In fact, a consortium has developed testing procedures that standardize the structural testing of their products--a key step in getting recycled-plastic lumber recognized in building codes. Still, recycled-plastic lumber has some shortcomings. The products are heavy, slippery, and lack wood's strength, and they heat up and soften somewhat in the sun. (Lighter-colored materials heat up less, making them better for decks.) Fluctuations in temperature cause them to expand and contract significantly.
Wood-plastic composites. Products made from a mix of recycled plastic and wood fiber are the other main category. These usually contain 50 percent HDPE and 50 percent wood waste. The wood reduces the weight of the lumber, improves its strength and stiffness, and reduces thermal expansion and contraction. Mobil Chemical developed Rivenite, the first wood-plastic composite, later called Timbrex, and finally Trex. At plants in Virginia and Nevada, a spin-off company called Trex produces its namesake wood-plastic lumber that matches the dimensions of conventional lumber (such as 2-by-4s).
AERT, Inc., of Junction Texas, produces decking and handrails marketed as ChoiceDek. These have deep corrugations on the underside that reduce weight without significant loss of rigidity. ChoiceDek is made using a mix of HDPE and low-density polyethylene (LDPE). For the wood fiber, the company uses oak or red cedar chips left over after extracting the aromatic oils. Because a consistent type of wood is used (rather than wood waste), ChoiceDek ages to a uniform silvery gray.
Several other composite products rely on highly engineered designs. SmartDeck, manufactured by U.S. Plastic Lumber, is a complete decking system, with planks, posts, railings, stair treads, trim, and fascia boards. Railings are hollow for easy installation of wires.
Another entry into this field is Nexwood, from Composite Technology Resources Ltd., in Quebec. This product is similar to SmartDeck, but it uses rice hulls--the very strong fiber left over after threshing rice. Wood products giant Louisiana-Pacific Corporation is expected to introduce a wood-plastic composite this year.
Fiberglass-plastic composite. U.S. Plastic Lumber recently introduced recycled-plastic lumber designed to carry structural loads. Carefree Structural Lumber incorporates fiberglass into recycled HDPE to greatly increase its strength. As a result, this product can be used as support structures for decks. Until now, most decks made with recycled-plastic decking used pressure-treated lumber for support structures (joists and posts).
Although not as common as pressure-treated or cedar lumber, more and more recycled-plastic lumber is being used around homes. Decking is the most common use. Plastic lumber replaces pressure-treated wood, and premium rot-resistant woods such as cedar, redwood, and teak.
In landscaping, recycled-plastic lumber, including commingled plastic products, can be used in retaining walls to stabilize steep slopes. The landscape timbers are bolted together or pinned into the ground. In gardens, plastic lumber is an alternative to preservative-treated lumber, for providing stakes, garden edging, and support for raised beds.
Another important application is for outdoor furniture such as picnic tables, garden benches, and lawn chairs. This furniture may be a little heavy, making it difficult to move around, but it won't rot and should last for years.
Recycled-plastic lumber, both products made from 100 percent plastic and from wood-plastic composites, can be installed using ordinary carpentry tools, though carbide blades are recommended for circular saws. (The plastic may melt or burn if a dull blade doesn't cut through it quickly enough.) All will accept nails, but stainless steel screws in predrilled holes are recommended.
Deck planking is the most commonly available material. It is usually noted as "5/4-by-6," a shorthand for 1-1/4-by-6 (actual dimensions 1 by 5-1/2 inches), and is available in various lengths. All require posts and supports made of pressure-treated wood (or Carefree Structural Lumber).
Compared to wood, plastic and composite lumbers are heavier and more subject to thermal expansion and contraction. Depending on the kind of wood being compared, plastic can weigh two to three times as much. Be sure to check manufacturer's specs regarding the size of gap to allow between boards both width-to-width and end-to-end. Most products specify a minimum width-to-width gap of 1/8 inch, plus another 1/8 inch for every 20-degree difference between installation temperature and possible maximum temperature. Basic end-to-end gaps are typically 1/16 to 1/8 inch; longer boards may need more.
When working with plastic woods, always wear a dust mask and work in an area with adequate ventilation. While it's not necessary, most can be painted or stained, though they won't hold the finish as well as wood does. Decking that is 100 percent plastic cannot accept paint and stain.
* SmartDeck is made of high-density polyethylene and oak sawdust. It fades to a warm silver gray. A 16-foot 5/4-by-6 costs $25 and weighs 43 pounds.
* ChoiceDek Classic is made of high- and low-density polyethylene and red cedar chips. It fades to silver gray. A 16-foot 5/4-by-6 costs $25 and weighs 33 pounds.
* Carefree Decking is made of high-density polyethylene. It's available in five non-fading colors: light gray, light silver, red-brown, beige, and white. A 16-foot 5/4-by-6 costs $28 and weighs 20 pounds.
* Trex is made of high- and low-density polyethylene and sawdust. It's available in tan and dark tan, both of which fade slightly, and dark brown, which is non-fading. A 16-foot 5/4-by-6 costs $23 and weighs 40 pounds.
Alex Wilson is editor and publisher of Environmental Building News, a monthly newsletter about environmentally responsible design and construction. He lives in Brattleboro, Vermont.
Article published on June 23, 2008.