How Good is Plastic Wood?Comments (0)
This article is from Issue 89 of Woodcraft Magazine.
You can build your next project with lumber that will never decay, crack, warp, or need finishing.
Three years ago I resurfaced my deck with composite boards made from recycled plastic and wood dust. Although I live in the rainy Northwest, a giant Petri dish for moss and mold, the deck still looks as good as the day I installed it. And the only maintenance I’ve done is a yearly scrub with soap and water.
That got me thinking about using synthetic lumber for other outdoor projects. It took a while, but I tried out the main types of plastic lumber shown here—everything from decking boards skinned with faux wood grain to lightweight PVC trim boards and bright-colored solid plastic stock. All of these varieties offer the advantage of excellent durability under tough outdoor conditions. Plastic lumber will continue to look great while real wood will show signs of damage from moisture, mold, sunlight, and insects. And there’s more good news too: You can build almost anything with plastic lumber, using the same power and hand tools you already own. But there are important considerations you’ll need to make when switching from real wood to plastic. I’ll go over some useful tips about cutting, shaping, and joining the material.
Even though plastic lumber is made almost entirely from bottles, bags, and other products rescued from the waste stream, it’s expensive to manufacture. Those costs are passed on to end-users, as you can see in the prices listed here. It’s also important to note that plastic boards are typically sold in long lengths. This can be an advantage if you’re building a deck, and picking up your material from a local supplier. But if you want small orders or shorter material shipped to you, it can be challenging to find a supplier. See the Buyer’s Guide on p. 70 for some recommendations.
- All plastic lumber except for PVC is made with 95% recycled material.
- Most plastic lumber is warrantied against weather damage for 20+ years.
- PVC boards can be glued with special adhesive, but glues won’t work on other types of plastic lumber.
- Changes in temperature cause plastic lumber to expand and contract.
Polyvinyl Chloride (PVC)
$3.75 - $5.63/bd. ft.
($30 - $45 for 1" × 6" × 16')
- Sold in sheets and as 3⁄4"-thick trim boards. PVC fencing, railing, and decking are also available.
- Trim and sheet stock are available in white only, but these materials can be painted.
- Can be glued using special PVC adhesive.
- More flexible than other types of plastic lumber.
- Available at lumber yards and home centers.
BEST USE: weatherproof trim and cladding
Plastic-capped decking boards
$5.00 - $8.75/bd. ft.
($40 - $70 for 1" × 6" × 16')
- Composite core (recycled plastic and wood dust),
- with wood-grain cap that protects core from wear, weathering, and mildew.
- Most common dimension is 1 × 51⁄2".
- Many boards come with grooved edges for use with hidden deck fasteners.
- Many wood tones available. Premium decking looks like real wood.
- Available at home centers and building supply stores, and by special order.
BEST USE: decking and projects that don’t require exposed ends or cut edges
Uncapped composite decking
$6.25 - $8.12/bd. ft.
($50 - $65 for 1" × 6" × 16')
- Made from a blend of recycled high-density polyethylene (HDPE) and wood dust/fibers.
- Most boards have a textured surface to simulate wood grain.
- Boards are available in common dimension
- lumber sizes, and in different wood tones.
- Surface will show slight weathering with age.
- Has the same composition through and through.
- Slightly stiffer than HDPE plastic lumber.
- Available by special order from home centers and building supply stores.
BEST USE: decking, outdoor railings, and outdoor furniture
High-Density Polyethylene (HDPE) lumber
$6.88 - $8.12/bd. ft.
($55 - $65 for 1" × 6" × 16')
- Sold mostly for commercial use in outdoor furniture, docks, and boardwalks.
- Available in many colors (with UV blockers added to minimize fading).
- Has the same composition and color through and through.
- Lighter than wood-plastic composites.
- More slippery than other plastic lumber.
- Available by special order
BEST USE: outdoor furniture
Tips for tackling plastic lumber projects
All types of plastic lumber can be worked with most of the same tools you use for woodworking, including (surprisingly) hand and power planes. Sandpaper will clog quickly, so edge-shaping should be done with a mill file, plane, or router.
PVC boards can be joined together with special adhesive, but all other plastic lumber can’t be glued. So you’ll need to join parts with screws or through-bolted connections.
Plastic lumber expands and contracts in reaction to temperature changes. Movement and strength issues should factor into the design of a plastic wood project (see Design Tips below). The cutting, shaping, and joinery details shown here will come in handy if you’re building with plastic lumber.
Cutting and Routing
Joining with Screws and Hardware
Take advantage of special hardware. For post-rail connections, cross-barrel fittings can be combined with plastic dowels to make strong, attractive joints. Use steel dowel centers as shown at left to mark plastic dowel locations as you close the joint.
Plastic plugs. Make short plastic dowels with a plug-cutting bit, then cut them free. Use the dowels in cross-barrel joints (facing page), or to hide counterbored or pocket screws.
Hide holes with a heat gun. Press plugs into place after heating the plug and the hole with a heat gun. No glue is necessary; just make sure both parts have been softened slightly before pressing a plug into place. Once the surface has cooled, trim the plugs slightly proud with a sharp knife, and then plane them flush.
- Plan to join parts together with bolts or screws.
- Test your design for flex. Plastic decking is designed for joists spaced on 16" or 24" centers. But for furniture like benches and tables, it’s smart to mock up supports and make sure your stock won’t deflect excessively under anticipated loads.
- Exploit the flexibility of plastic lumber. You can design projects with curved parts. Heating will increase plastic lumber’s flexibility.
- For boards with trapped ends, leave a 1⁄16" gap for every 4' of length.
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