TECH TALK: WORKING WITH PLASTIC LUMBER
Plastic lumber can be cut, drilled, routed, and fabricated using many conventional woodworking tools. However, it does not always behave like wood. The material formulation, temperature, tooling, fastening method, and intended application can all affect the finished result.
The following are practical starting points—not universal installation instructions. Always confirm the requirements for the specific product being used and consult the manufacturer or an appropriate qualified professional when the application is structural or otherwise critical.
PLAN FOR BOARD MOVEMENT
Plastic lumber expands and contracts as its temperature changes. When boards meet end to end, allow the spacing recommended for the particular product, board length and installation temperature.
Where the design permits, cutting adjoining ends at a 45-degree angle may create a less abrupt joint and reduce the likelihood of the two ends meeting squarely if movement occurs. An angled joint does not eliminate the need for proper expansion clearance.
Because HDPE plastic lumber moves with temperature, getting your butt-joint gaps right during installation prevents summer buckling and winter gaps.
Installation Temp Butt-Joint Gap Why It Works
Above 70°F 1/8" Pre-expanded material requires minimal clearance.
40°F to 70°F 3/16" Balanced clearance for year-round temperature shifts.
Below 40°F 1/4" Maximum clearance allowed for contracted cold-weather boards.
KEEP THE MATERIAL AT A CONSISTENT TEMPERATURE
Before measuring and cutting, keep the boards together in a shaded location so they remain as close as practical to the same temperature. If the material has been sitting in direct sunlight, allow it to stabilize before making critical measurements or cuts.
A light-colored, breathable cover may help shield boards from direct sunlight. Do not wrap the material in a way that traps heat.
SHARP TOOLS MAKE BETTER CUTS
Heat buildup is one of the biggest concerns when drilling, cutting, routing, or milling plastic lumber. Sharp tooling, appropriate cutting speed, and steady material removal help produce cleaner results.
Dull tools create unnecessary friction and heat. Allow chips to clear, avoid forcing the tool, and pause when necessary to prevent excessive heat buildup.
DRILLING
Sharp drill bits make faster, cleaner holes. Carbide-tipped tooling is commonly used for plastic lumber and can be particularly helpful when working with fiberglass-reinforced structural material, which may wear conventional tooling more quickly.
Support the material properly and consider using a backing board when drilling through it to help reduce breakout at the back of the hole.
CUTTING
Avoid very fine-toothed saw blades that do not provide enough room for chips to clear. We have generally found that sharp, carbide-tipped blades with adequately spaced teeth remove material more effectively and reduce heat buildup.
The appropriate blade, tooth count and cutting speed may vary with the product’s formulation, thickness and reinforcement. Confirm the manufacturer’s recommendations before beginning production work.
ROUTING AND MILLING
Plastic lumber can be routed, milled, notched and shaped for many applications. Keep cutting edges sharp, use light and steady pressure, and avoid feed rates that generate excessive heat.
Fiberglass-reinforced structural plastic lumber can be abrasive. Carbide- or diamond-coated tooling may provide longer service life when performing repeated fabrication.
STAINLESS STEEL FASTENERS: GRADE MATTERS
We generally recommend stainless steel fasteners with plastic lumber, but selecting the correct grade matters for long-term performance and satisfaction.
304 — General Purpose
Suitable for most ordinary indoor and outdoor applications. Use 304L when welding is required. Avoid prolonged exposure to saltwater, pool chemicals or other chlorides.
316 — Marine and Coastal
Provides better resistance to saltwater, chlorine and aggressive chemicals. Consider 316 for marine, coastal, poolside and demanding industrial environments.
303 — Machining Grade
Machines easily and works well for turned parts such as pins, shafts and fittings. It has lower corrosion resistance and generally should not be used for welded assemblies.
The fastener grade should match the environment and the other materials being joined. When uncertain, confirm the selection with the fastener supplier or project professional.
CONCEALING FASTENERS
If fasteners need to be concealed, use a compatible plug, cap or manufacturer-approved finishing method. Do not assume that plastic shavings can safely be melted back into the board with an open flame. Heating can alter the surface, create an inconsistent repair and introduce unnecessary fire and vapor hazards.
Ask the manufacturer or us about suitable fastening and finishing options for the specific material.
A FEW IMPORTANT REMINDERS
• Confirm whether the material is structural or non-structural.
• Verify actual dimensions rather than designing only from nominal sizes.
• Account for expansion and contraction.
• Use sharp, appropriate tooling.
• Control heat and allow chips to clear.
• Wear suitable eye, hearing, hand and respiratory protection for the work being performed.
• Follow the product manufacturer’s current fabrication and installation instructions.
SHARE YOUR FIELD TIP
These are only a few of the practical lessons we have collected while working with plastic lumber.
We intend for this page to grow rather than remain stagnant—and we would welcome your help.
If you have developed a useful cutting, drilling, fastening, fabrication or installation technique, send it to us.
After reviewing it, we may add it to this page and give you a well-earned shout-out by including your name and company alongside the tip.
Good information becomes more valuable when it is shared.
