Robinia or sweet chestnut – the comparison

Robinia series · Focus: comparing timber species

Europe's two great outdoor hardwoods, compared point by point – without caricature.

Sweet chestnut is the traditional benchmark for outdoor timber in France: cleft palings, stakes, shingles, flooring – centuries of loyal service. Robinia – also known as black locust, and often sold as acacia – is its challenger: denser, more durable, and at home in the same uses.

Both deserve better than a slogan. Here is what the standards, the figures and field experience say – including where sweet chestnut remains an excellent choice.

~30 years vs ~15

indicative service life of a stake in ground contact: robinia vs sweet chestnut

Round robinia stakes on a pasture fence: ground contact is where the difference between species shows.

Durability: class 1-2 vs class 2

The EN 350 standard rates the natural durability of timber against fungi from 1 (very durable) to 5 (not durable). Robinia heartwood (Robinia pseudoacacia) is rated class 1 to 2 – it is the only European hardwood that can be used in use class 4 (permanent contact with the ground or fresh water) without any treatment. Sweet chestnut is rated class 2 (durable): a very good level for a European timber, and the chestnut trade claims it for use class 4.

In the field, the difference is measured in years: a sweet chestnut stake lasts in the region of 15 years in ground contact, a robinia stake about 30. As raw material, sweet chestnut costs 15 to 40 % less; per year of service, the sum is reversed – especially once you count the labour of replacement.

Mechanical properties: robinia is in a class above

A density of about 740 kg/m³ against 640 for sweet chestnut, markedly higher bending strength (126 MPa against 71), and a hardness that makes the difference: on the Janka scale, robinia reaches about 7,560 N against about 3,010 N for sweet chestnut – about two and a half times as hard. (In the French Monnin test, NF B 51-013, robinia scores about 9.5 against ~2.9 for sweet chestnut.) Robinia allows slimmer sections for the same strength, withstands impacts better (grape harvesters, livestock) and holds its fixings more firmly. Sweet chestnut, lighter and softer, is easier to handle and machine – and it splits remarkably well, which is what made its name in cleft palings.

Criterion	Robinia	Sweet chestnut
Natural durability (EN 350)	Class 1-2	Class 2
Use class 4 without treatment	Yes – the only European hardwood	Claimed, more debated
Stake in ground contact	~30 years	~15 years
Density at 12 % moisture content	≈ 740 kg/m³	≈ 640 kg/m³
Bending strength	≈ 126 MPa	≈ 71 MPa
Tannins (run-off staining)	Virtually none	Heavy – black stains possible
Splitting (cleft palings, stakes)	Difficult (hard, lively timber)	Excellent – its traditional strength
Raw material price	Higher	15 to 40 % cheaper
Supply chain	Romania (dense stands)	France (Brittany, the South-West, the Cévennes)

Tannins: the point that makes the difference on a façade

Sweet chestnut is a very tannic timber: with the first rain, its tannins migrate and leave brown-black streaks on render, stone and pool copings – to the point that dedicated "tannin-blocking" products exist. Robinia contains almost none: its extractives (robinetin, which gives it its durability and yellow colour) stay in the wood. For cladding, for a fence alongside a light-coloured wall, or around a stone terrace, this is often the deciding criterion.

Finger-jointed robinia cladding being installed: with no migrating tannins, the render and plinth stay clean.

Where sweet chestnut remains a good choice

Let's be honest: sweet chestnut has real arguments. Its price, first of all, and its dense French supply chain – Brittany, Périgord, Limousin, the Cévennes, Corsica – which allows very short supply chains there. Then its lightness and the ease with which it splits and machines: a cleft sweet chestnut paling remains an excellent product, and for any above-ground use – palings, screens, balustrades – the durability gap matters much less: it is contact with the soil that widens the difference. Finally, France does have a real robinia resource – around 220,000 ha – and French sawmills already make good use of it. It simply isn't enough for the volumes and long lengths we deliver all year round, which is why we source from the large, dense stands of Romania.

Sanded robinia cleft palings, in the roll and installed: on sweet chestnut's signature product, the two species run close.

Key points

· Robinia: durability class 1-2 (EN 350), the only European hardwood in use class 4 without treatment – ~30 years in the ground against ~15 for sweet chestnut.

· Clear-cut mechanical properties: ≈ 740 kg/m³, markedly higher bending strength and about two and a half times the hardness (Janka ~7,560 vs ~3,010 N) – slimmer sections, better fixing hold.

· Tannins: sweet chestnut bleeds (black stains), robinia hardly at all.

· Sweet chestnut keeps the advantage on raw material price (15 to 40 % less), lightness, easy splitting and a local supply chain in France.

· Compare the cost per year of service, not the purchase price.

Frequently asked questions

Is sweet chestnut a use class 4 timber?

The sweet chestnut trade claims use class 4, and EN 350 rates it durable (class 2). In practice, in permanent ground contact, a sweet chestnut stake lasts in the region of 15 years, against about 30 for robinia, rated class 1-2. For above-ground use (cladding, furniture), on the other hand, sweet chestnut is perfectly at home.

Why does sweet chestnut stain façades?

Because it is rich in water-soluble tannins: rain carries them out and they oxidise into brown-black streaks on render, stone and concrete. It is an aesthetic issue, not a durability defect – but it is hard to put right. Robinia, with virtually no free tannins, does not cause these streaks – an advantage also covered in our pergola guide, where the question arises above a stone terrace.

Cleft palings: sweet chestnut or robinia?

Cleft sweet chestnut is the traditional paling – the chestnut paling familiar across Britain: light, easy to split, part of the landscape. On this particular product, however, the price gap has narrowed: a sweet chestnut paling is far from cheap, and our robinia cleft palings made from sawn stakes sit at the same level. The choice therefore comes down to service life, which is markedly longer with robinia – a real advantage by the sea or on dunes, where replacement is expensive. The choice by use is set out in our article "Robinia fencing and cleft palings – choosing by use".

Is robinia really twice as durable as sweet chestnut?

In ground contact, yes, that is the order of magnitude observed: about 30 years against about 15 for comparable stakes, sapwood excluded. Above ground the gap narrows – both species then last for decades – and the choice depends rather on mechanical properties, tannins and appearance.

Further reading

Reference guide: "Robinia outdoors – the complete guide".

See also: "Robinia or pressure-treated pine (use class 4) – the comparison" (the other major comparison) · "Robinia fencing and cleft palings – choosing by use" · "Round, sawn or split stakes – which to choose (sapwood and durability)".

Our products: Round stakes · Cleft palings · Large posts · Agricultural posts.

Contact: Torn between the two for a specific project? Describe the use and the exposure: the sawmill will tell you honestly which to choose.

Disclaimer. Non-contractual article, provided for information only (photos and drawings included). Robinia is a natural material: the values given are orders of magnitude and may change without notice; in case of discrepancy, only the product’s technical data sheet and the general terms of sale apply. Always check the regulations that apply to your project.

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