Bookmark and Share
Standardization News Search
Tech News
ASTM Specifies Plastic Lumber for Exterior Decking

Due to the hardy recycled-plastic content of plastic lumber which repels water and insects, its use in traditional wood applications is growing. In July, ASTM released D 6662, Standard Specification for Polyolefin-Based Plastic Lumber Decking Boards. The brainchild of engineers, manufacturers, and recyclers in Committee D20 on Plastics, the specification was developed to bring uniform quality requirements to polyolefin-based plastic lumber products used as exterior residential decking.

The specification details a procedure to calculate recommended span lengths for spacing of support joists. This procedure was developed using experimental data from a typical unreinforced plastic lumber made predominantly from recycled high-density polyethylene. The methodology to develop span lengths for other types and compositions of plastic lumber is detailed in an appendix of D 6662.

D 6662 defines plastic lumber as a manufactured product of more than 50 weight percent resin generally rectangular in cross-section and typically supplied in sizes corresponding to traditional lumber board and dimensional lumber sizes. It may be filled or unfilled and composed of single or commingled resins.

“Plastic lumber materials are inherently rot- and insect-resistant and don’t require chemical treatments or coatings to have or maintain this resistance,” said Richard G. Lampo, a materials scientist in the Materials and Structures Branch at the U.S. Army Corps of Engineers’ Laboratory, Champaign, Ill. “This translates into very low maintenance needs for the life of the material which can be especially beneficial to the user as the overall life-expectancy of plastic lumber can be several times that of traditional wood materials in outdoor applications. These plastic lumber products, made predominantly from recycled plastics, also help divert significant amounts of waste plastics otherwise destined to landfill—and that amount will increase as the market continues to grow.

“The development of the latest standard for plastic lumber decking boards is noteworthy since it will not only make it easier for users to specify plastic lumber decking,” he concluded, “but it also further paves the way for the development of standard designs and material specifications to construct all-plastic lumber structures—for example, the plastic lumber boardwalk and observation deck constructed at Fort Belvoir, Va., where structural-grade plastic lumber was used for the underlying support structure and railing system.” (See photo.)

Lampo chaired a group of approximately 50 members of Section D20. 20.01, Manufactured Recycled Plastic Lumber and Shapes, who have developed a total of eight standards for plastic lumber since 1997 (including D 6662):

D 6108, Standard Test Method for Compressive Properties of Plastic Lumber and Shapes;
D 6109, Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastic Lumber;
D 6111, Standard Test Method for Bulk Density and Specific Gravity of Plastic Lumber and Shapes by Displacement;
D 6112, Standard Test Method for Compressive and Flexural Creep and Creep Rupture of Plastic Lumber and Shapes;
D 6117, Standard Test Method for Mechanical Fasteners in Plastic Lumber and Shapes;
D 6341, Standard Test Method for Determination of the Linear Coefficient of Thermal Expansion of Plastic Lumber and Plastic Lumber Shapes Between -30&Mac251;F and 140&Mac251;F (-34°C and 60&Mac251;C); and
D 6435, Standard Test Method for Shear of Plastic Lumber and Shapes.

Additional standards under development by Section D20.20.01 include a new specification for plastic lumber materials for bending member applications, such as joists and beams, and a standard practice for plastic lumber deck design and construction.

For further technical information, contact Richard G. Lampo, Materials and Structures Branch, Facilities Division, U.S. Army Engineer Research and Development Center–Construction Engineering Research Laboratory, Champaign, Ill. (phone: 217/373-6765). Committee D20 meets Nov. 4-7 in Dallas, Texas. For meeting or membership details, contact Kathie Morgan, director, ASTM Technical Committee Operations (phone: 610/832-9721).

To learn more about plastic lumber, consult the Web site of the Plastic Lumber Trade Association. //

Copyright 2001, ASTM