Gardening Articles: Landscaping :: Yard & Garden Planning
Would-Be Wood (page 2 of 3)
by Alex Wilson
Three Main Choices for Lumber Substitutes
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).