Robinia or composite decking – the comparison

Ferdinand Terlinden

1 day ago

5 min read

Robinia series · Focus: comparing materials

The timber that asks for nothing, against the material that promises to ask for nothing.

WPC composite decking – wood flour bound in plastic – has conquered terraces with a simple promise: zero maintenance, zero splinters, zero surprises. The promise is partly kept, and that should be said. The solid-timber alternative is robinia – also known as black locust, and often sold as acacia.

But a material should be judged over thirty years: what becomes of it in the sun, under scratches, and in the skip. On these three points, solid use class 4 timber has arguments that few sales brochures spell out.

100 % landfill

the end-of-life scenario for a composite decking board, according to the environmental product declaration (the French FDES) of the market leader in France

Circular deck in solid robinia boards in a public garden, solid timber that can be sanded and repaired — Round deck in robinia boards in a public garden: solid timber that can be sanded and repaired board by board.

What a composite decking board really is

Compared with solid robinia (Robinia pseudoacacia), a typical composite board is a very different product. It contains a little over half wood flour, about 30 % high-density polyethylene (HDPE) and the rest additives and pigments. It is neither wood nor quite plastic: it is an extruded, calibrated, uniform profile – its great strength – that must be laid on a joist substructure, often aluminium. Its reference service life, the one the manufacturer itself uses to calculate its environmental impact, is 25 years; warranties range from 10 years (commercial use) to 25 years (residential).

A detail that matters: these warranties cover splinters, fungi and insects – but expressly exclude UV discolouration, scratches and wear to the appearance. In other words: what you can see is not guaranteed.

Head to head, point by point

Criterion	Robinia (naturally use class 4)	WPC composite
Composition	100 % timber, no treatment	≈ 55 % wood flour + ≈ 30 % PE + additives
Service life	25-40 years depending on use	15-25 years (25 years as the FDES reference)
Summer, bare feet	Stays relatively cool	60-70 °C reported on dark colours
Scratches, burns	Can be sanded out, restored	Permanent – and not covered by warranty
Appearance over time	Turns grey (reversible patina)	Stable colour, UV discolouration not covered
Splinters	Possible (rare on brushed timber)	None – covered by warranty
Maintenance	Nothing compulsory	Washing with water
Board price	comparable to entry-level hollow composite	€60-90/m² (hollow) to €100-140 (co-extruded)
End of life	Timber: firewood, compost	Landfill (no recycling route exists)

Summer: the real test

A deck is lived on barefoot in July. Yet composite, especially in dark colours, heats up strongly in the sun: reported measurements reach 60 to 70 °C, to the point that some manufacturers themselves advise against walking on it barefoot in the hottest hours and recommend light colours. Solid timber heats up markedly less and dries quickly after a storm. Around a swimming pool, weigh this against the – real – argument of zero splinters.

Robinia (acacia) sun lounger and surround beside a swimming pool in full sun, timber that stays comfortable barefoot — South-facing robinia pool surround: solid timber stays comfortable underfoot, even at the height of summer.

Thirty years on: the skip or the stove

This is the item brochures never show. The official environmental product declaration (the French FDES) for a leading French composite board states about 50 kg of CO₂ equivalent per square metre over its life cycle – and an end-of-life scenario of 100 % landfill: with a third of plastic intimately mixed with the wood, neither timber nor plastic recyclers want it. The "recyclable" claim for composite remains theoretical. A robinia board at the end of its service, by contrast, is still wood: it can be burnt, composted or reused – and throughout its life it has stored carbon.

Where composite genuinely wins

Two points, and they are serious ones. First, guaranteed zero splinters and perfect uniformity: identical sections, consistent colours, no knots – for a pool deck used by children, that is an argument to respect. Second, maintenance: nothing to do beyond washing, never any greying to accept or oil to consider. Robinia doesn't require anything either – but it turns grey, and keeping its honey colour means applying a decking oil every 2-3 years. It is up to each of us to decide what we want to look at for thirty years.

Sanded robinia pergola on a beach in the south of France, solid timber that can be repaired by sanding — Sanded robinia pergola on a beach: sand, salt and UV – and a surface that can be restored by sanding.

Key points

· Composite = ≈ 55 % wood flour + ≈ 30 % plastic; reference service life 25 years – use class 4 robinia lasts 25-40 years depending on use.

· Composite warranties exclude discolouration, scratches and wear to the appearance; a scratch cannot be repaired, robinia can be sanded.

· Heat: 60-70 °C reported on dark composite in full sun – solid timber heats up far less.

· End of life: composite boards go to landfill (no recycling route); robinia boards are burnt, composted or reused.

· Composite keeps the edge on zero splinters and uniformity – the pool and children's-feet argument.

Frequently asked questions

Does composite decking get hotter than timber decking?

Yes, noticeably – especially in dark colours: reported measurements reach 60 to 70 °C in full sun, and some manufacturers themselves advise against walking on it barefoot in the hottest hours. A light colour takes off 10 to 15 °C. Solid timber heats up markedly less and releases heat more quickly.

Can a scratched composite board be repaired?

No: a scratch, a barbecue burn or an ingrained stain cannot be sanded out – the manufacturer's solution is to replace the board, and this cosmetic damage is excluded from warranties. Solid timber, on the other hand, can be sanded, restored and brought back.

Is composite decking recyclable?

In theory, WPC can be re-extruded; in practice, there is no working collection and recycling route: the environmental product declaration (the French FDES) of the market leader in France assumes an end-of-life scenario of 100 % landfill. An intimate mix of wood and plastic interests neither timber recyclers nor plastic recyclers.

How long does composite decking last?

From 15 to 25 years depending on the range – 25 years being the reference service life used by the manufacturers themselves and the ceiling of residential warranties. That is respectable, but no better than timber: a use class 4 robinia deck, properly installed (ventilation, gaps, fall), lasts through the same decades – and can be repaired.