Recycled plastic lumber is a product made from recovered plastic or recovered plastic mixed with other materials, which can be used as a substitute for concrete, wood, and metals. It is produced in sizes and shapes (profiles) typical in the lumber industry. Because of its resistance to decay, plastic lumber is an excellent material for decking, landscaping, and recreational equipment, particularly where it comes into contact with soil or water.
The technology for manufacturing recycled plastic lumber has been in place
since the early 1980s. Plastic lumber is most commonly manufactured from
post-consumer high density polyethylene (HDPE), but linear low density
polyethylene (LLDPE) and low density polyethylene (LDPE) are also used. These
plastic feed stocks are derived from such raw materials as post-consumer milk
jugs, grocery bags, plastic wrap, bubble rap, detergent bottles,
and water bottles, and other used plastic commodities.
The recovered plastic is cleaned, shredded, and ground. The material is then
melted and mixed with UV stabilizers and pigments
then it is molded or extruded into typical lumber shapes, (2x4 4x4, etc),
or other shapes. This plastic lumber can then
be transformed by consumers and manufacturers into a wide range of products
including decks & docks, landscape timbers, parking stops, picnic tables,
benches, trash receptacles, planters, and numerous custom applications.
There are several types of plastic lumber:
Wood/Plastic composites
Usually a blend of 50 percent plastic is mixed with
sawdust or other recycled fiber. This material is a little stiffer
than all-plastic lumber, but is less expensive
which makes it very popular with home owners. This
material is primarily used for decks and docks with
most companies now offering
boards that look less like plastic and have a wood-grain texture
that come in a variety of colors. The wood fibers are
encapsulated in plastic. As with wood, these composites need to be cleaned and
maintained according to manufacturers care instructions because they will show stains like wood and there can be mold and mildew problems.
Fiber-Reinforced
Fiber-reinforced plastic lumber consists of plastic mixed with chopped or
continuous strands of glass fiber. The initial cost of this type
is the
highest of all, but its benefits are also greater, as it is
the strongest of the three and may be used for structural
applications.
Product Benefits
Purchasing Costs
Recycled plastic lumber currently has a higher purchase price (initial cost) than virgin wood, but
lasts longer than wood. When maintenance, replacement, and
disposal
costs are included in the analysis, recycled plastic products
are the best value.
Purchase prices of plastic lumber are expected to decrease as technology improves and demand increases. Wood prices are expected to continue to increase. More and more of these plastic alternatives are available at your local hardware/lumber retail store.
King County agencies have used and evaluated several recycled plastic products, including plastic "lumber", can-liners, bench slat replacement, truck sideboards, playground equipment, bollards, and other products.
The Renton Maintenance Facility of the Fleet Administration Division requires new dump trucks to be outfitted with recycled plastic sideboards before delivery. High-quality old growth Douglas-fir had been conventionally used in this application, but it is increasingly scarce and expensive. Since 1996, they have used recycled plastic because it is more impact-resistant and needs to be replaced less frequently, saving money in the long-term despite its higher initial cost. Replacement was immediately reduced from two wooden sideboards per week to less than one plastic sideboard per month which saves $10,000 per year in materials costs alone.
The King County Parks and Recreation Division has used recycled plastic lumber since 1993 for various applications, such as benches, tables and boardwalks. In 2005, because of the durability and low maintenance of these products, they purchased fifteen six-foot recycled plastic picnic tables for the Tolt River Campground at a cost of less than $7,000.
Stadium Administration Maintenance Section personnel used recycled plastic lumber to replace wooden 4"x4"x8’ "channel boards" to secure the Kingdome artificial turf from 1994 to 2000. The performance of this material proved superior to that of virgin lumber and demonstrated a longer replacement schedule and lower life-cycle cost. The use of recycled plastic lumber for channel boards was also adopted by other stadia, including the Minneapolis Metrodome and B.C. Place in Vancouver B.C., Canada. The County-operated stadium was demolished in 2000 to make room for a new football stadium.
The City of Seattle regularly uses recycled plastic lumber for their Park Rainbow Signs and have used in in various applications in their parks from pier-decking to a pedestrian bridge in city parks.
Pictures of recycled plastic park products
Bid and Contract Specifications
ASTM Recycled Plastic Lumber Standards
ASTM International has played an important role in creating standardized, material-appropriate testing methods for recycled plastic lumber and developing purchasing specifications.
Follow these links to a free summary of the ASTM standards. Each reference includes information on how to purchase the full standard.
Standard Test Methods for Plastic Lumber:
King County
Plastic lumber contract provisions - Equipment Shop, Fleet Administration
- Language used in new dump truck contracts:
- Sideboard Pockets: 3/16” front and rear pockets with side boards (3” x 10”) one piece recycled plastic. Two equally spaced inner/outer sideboard supports per side.
Recycled Plastic Pedestrian Bridge
Meadowbrook Pond, City of Seattle (1996)
The City of Seattle built a recycled plastic pedestrian bridge in 1996 across a stormwater retention pond. They decided to use recycled plastic lumber because Thorton Creek was being rehabilitated as a salmon stream.
At the time, plastic lumber was very new to the marketplace, not widely available, and did not have a long usage history. The design team had to make adjustments to their original wood design because plastic is a very different material than wood. Three different types of plastic lumber were sourced for this project:
- Recycled plastic 8"x8"s, reinforced with four steel bars (re-bar), were used for pilings and support members. The cost was approximately 1.5 times the cost of treated lumber.
- Fiberglass reinforced recycled plastic 2"x8"s were used for the joists, at a cost of about 2.7 times that of treated lumber.
- Recycled plastic/wood composite 2"x6"s were used for decking at a cost of about twice that of treated lumber.
This is probably the largest project that the City has done using recycled plastic lumber, but they have done several plastic lumber decking projects, park rainbow signs, truck sideboards and more.
The City of Seattle regularly uses recycled plastic lumber for their Park Rainbow Signs
Specific information on applications described in this publication may be obtained by contacting:
Other information
Bob Villa article on wood deck alternatives
- Health Building Network's Guide to Plastic Lumber (June, 2005)
- Plastic Lumber Product Ratings
Further information may be available through the following main menu selections:
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Updated: September, 2006
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