Working with Recycled Plastic Lumber: Cutting, Drilling, Fixing & Thermal Expansion

Solid recycled plastic lumber handles differently from timber in several important ways. This guide covers everything you need to know before you make your first cut — including the most common installation mistakes and how to avoid them.

Tools Required

Solid recycled plastic is a dense material. Standard woodworking tools work, but with important modifications:

Saw

Circular saw or table saw: suitable with the correct blade
Recommended blade: TCT (tungsten carbide tipped) crosscut blade, 40–60 teeth
Blade speed: use a slower feed rate than timber — plastic generates heat and needs time to clear chips
Hand saw: works for short cuts but takes more effort than softwood

Do not use a fine-tooth metal cutting blade — it will overheat the plastic and weld the cut shut.

Drill

Standard HSS or cobalt drill bits work well
Tip: keep drill speed moderate (not maximum), apply firm pressure, and occasionally withdraw the bit to clear chips
Pilot holes are mandatory before screwing into solid recycled plastic — the material is dense and will split or crack if you drive fasteners directly without piloting

Planer / Router

TCT cutters work well
Reduce feed speed compared to timber — plastic can melt if cutters are blunt or feed rate is too fast
Keep cutters sharp; replace at first signs of burning

Cutting Recycled Plastic Boards

Crosscutting (Cutting to Length)

Straightforward with a TCT circular saw. Support the board fully on both sides of the cut to prevent binding.

Ripping Lengthways

Avoid where possible. Ripping creates long, thin off-cuts that can flex and bind in the blade, causing burning and potential kickback. If ripping is unavoidable:

Use a table saw with a TCT rip blade
Use a push stick
Feed slowly and steadily

Notching

Do not make deep internal notches in load-bearing boards or posts. Unlike timber, recycled plastic does not have grain structure to resist crack propagation from a notch corner. If a notch is needed in a structural element, reinforce with a secondary fixing or redesign the joint.

Surface notches for drainage (e.g., 3–5mm on the underside of deck boards at joist positions) are fine.

Drilling and Fixing

Always Pilot-Drill First

This is the single most important rule. Solid recycled plastic is approximately twice as dense as softwood. Driving screws without piloting creates stress concentrations that can cause the board to crack — sometimes immediately, sometimes weeks later as thermal cycling applies additional stress.

Pilot hole diameter should be 90–95% of the screw shank diameter (slightly smaller than for timber because you want thread engagement, but the material doesn't compress the same way wood does).

Countersinking

Countersink to the full head depth so the screw head sits flush or just below surface level. Do not overtighten — the material does not compress like timber and stripped holes are hard to repair.

Fastener Choice

Stainless steel screws are strongly recommended, particularly in outdoor or ground-contact applications. The material itself will last 25+ years; your fixings should match that lifespan.
Avoid galvanised or zinc-plated screws in ground-contact positions — these will corrode and stain long before the plastic material needs replacing.
Hidden clip systems are available for decking applications and avoid the need for visible screw heads.

Fixing Through the Board Face (Decking)

For face-fixing deck boards, use two screws per board per joist crossing, positioned 20–25mm from the board edge. Pilot drill each hole.

Thermal Expansion: The Most Important Installation Detail

Solid recycled plastic expands and contracts with temperature more than timber does. The expansion coefficient for mixed recycled plastic is approximately 1.5–2.0mm per metre for every 10°C temperature change.

What This Means in Practice

A 3.6m deck board installed at 10°C will be approximately 3–5mm longer on a 30°C summer day. Over a 20-board deck run that's a significant cumulative movement.

If you don't allow for expansion:

Boards will buckle in summer heat
Boards will pull fasteners and crack around fixing points
End-to-end runs will push against walls or fixed fascias, causing visible distortion

Expansion Gap Rules

Between board ends and fixed structures (walls, fascia boards): Leave minimum 10mm gap at all fixed ends. We recommend 12–15mm if the deck is on a south-facing aspect or in a location with large day/night temperature swings.

Between boards (face-fixed): Leave 5mm gap between board faces for drainage and air circulation. This does not change significantly with temperature because the boards are fixed individually.

End-to-end joints in long runs: If you need to join boards end-to-end for a long run:

Centre the join over a joist
Leave a 10mm gap between board ends
Use a simple butt joint, not a finger joint (finger joints restrict thermal movement)

Installation temperature matters: Ideally install at a moderate UK temperature (10–15°C). Installing at 5°C in January means the boards will be at their shortest — leave the full 12–15mm expansion gap. Installing at 25°C in August means the boards are near their maximum length — a 5mm gap at ends may be sufficient, but 10mm is safer.

Cleaning and Maintenance

Solid recycled plastic requires essentially no maintenance, but here is what you can and cannot do:

Safe Cleaning Methods

Warm water and a stiff brush: removes most surface dirt
Pressure washer: safe and effective. The material is impervious to water — there is no risk of surface degradation from jet washing as there is with timber or some composite boards.
Mild household detergent: safe, rinse thoroughly after use
Diluted bleach solution (5%): can be used for stubborn algae or staining on the surface. Rinse immediately. Note: any surface algae on recycled plastic is just surface growth (the material itself provides no nutrients) and cleans off easily.

What to Avoid

Paint or stain: the material does not accept paint well, and adhesion will fail over time. The colour is pigmented throughout the board and does not need painting.
Oil or decking treatment: unnecessary and not effective. Oils do not penetrate the material.
Strong solvents: avoid acetone, paint stripper, or similar — these can surface-damage recycled plastic

Storage and Handling on Site

Store boards flat on a level surface, supported at regular intervals (max 600mm) to prevent sagging under their own weight in hot weather
Keep boards out of direct sun if storing for an extended period in summer — not because UV damages the material, but because boards stored at high temperature can be installed at maximum length (see thermal expansion section)
Boards are heavier than hollow composite equivalents — plan lifting accordingly

Quick Reference: Key Numbers

| Parameter | Value | |---|---| | Thermal expansion | ~1.5–2.0mm per metre per 10°C | | End gap (wall/fascia) | 10–15mm | | End gap (board-to-board) | 10mm at joins | | Pilot hole diameter | ~90–95% of screw shank | | Joist spacing (deck boards) | 300–400mm centres | | Board support spacing (storage) | Max 600mm centres |

Questions?

If you have a specific installation situation that isn't covered here — unusual ground conditions, very long board runs, or a mixed system — contact our technical team. We'd rather answer your question before installation than after.