Robinia street furniture: the council's calculation

Ferdinand Terlinden

1 day ago

8 min read

Robinia series · Choosing by use

Whole-life cost, maintenance, repairability and documents for a public tender

A bench or picnic table in robinia — also known as black locust, and often sold as acacia (Robinia pseudoacacia) — lasts around 30 years in ground contact, against about ten years for use class 4 pressure-treated pine. Robinia reaches durability class 1-2 (EN 350) and meets use class 4 (EN 335) just as it leaves the sawmill.

The consequence is financial: the furniture leaves the workshop finished and stays in service in that state, with the maintenance budget reduced to cosmetic cleaning and one-off replacements. The right unit of comparison becomes the cost per year of service, set out in “The price of robinia explained”.

~30 years against ~10

Service life of robinia in ground contact, without any preservative, compared with use class 4 pressure-treated pine.

Public bench with Corten steel ends and solid robinia slats, street furniture with no paint or treatment — Bench with Corten steel ends and robinia slats: the combination works because both materials weather on their own — the steel under its own patina, the wood by turning grey — and neither is ever repainted.

What does a local council really ask of its street furniture?

A technical services department's requirements come down to five points: last fifteen to twenty years, need no scheduled work, withstand knocks and graffiti, injure no user, and be repairable without tying up a team. The right indicator is therefore not the purchase price but the cost per year of service: purchase, installation and maintenance combined, divided by the number of years in service.

Public procurement adds its own constraints. The need is described in a tender specification — the document that defines what the contractor must deliver — and that document may not name a brand or a supplier. A council must also be able to obtain identical replacement parts years after the contract.

What is made in robinia for public spaces?

Robinia covers most outdoor furniture: benches and seating, picnic tables, litter bins, planters and raised beds, bollards and posts, barriers and railings, shelters and canopies, boardwalks and pontoons, seafront furniture. Children's play equipment falls under a separate standard, EN 1176, covered in the article on playgrounds.

Acacia Bois supplies materials and components rather than a catalogue of furniture: sanded posts up to 10 m as standard, up to 13 m and 40 cm in diameter as non-standard, boards, finger-jointed decking boards, shingles, end-grain wood pavers. Our public-space projects include bus shelters roofed with robinia shingles and seafront furniture exposed to salt spray.

Robinia (acacia) passenger shelter roofed with shingles, untreated timber furniture for local councils — Shelter roofed with robinia shingles: because the sawmill produces to order, the same pieces can be remade one at a time years later, without taking the structure apart.

Why robinia rather than treated timber or tropical hardwood?

Robinia meets use class 4 (EN 335) — permanent contact with the ground or fresh water — without chemical treatment. That removes two items: the preservative to be re-applied to cuts and machined surfaces, and the explanation owed to users about what has gone into a bench they touch. See “Robinia or pressure-treated pine (use class 4) – the comparison”.

The density of robinia, around 740 kg/m³, explains how well it takes knocks. European robinia also avoids drawing on tropical forest — ipe has been listed in CITES Appendix II since 25 November 2024 — and the supply chain is traceable: certificate FSC® C153588, chain of custody SGSCH-COC-011793, EUDR documentation (EU 2023/1115). See “Is robinia an ecological timber?”.

The picnic table: the textbook case for solid timber

A separate word on the picnic table, the item councils ask for most and by far the most abused in their stock. People stand on it, sit on the tops, put loads on it, drag it from one end of the lawn to the other, and it spends the winter outside. This is where solid timber makes the difference. A robinia top in a heavy section, in heartwood with the sapwood removed, does not warp, does not wear hollow under heels and does not break when a group sits on the same side. Nothing glued, nothing veneered, nothing painted: full section, in a timber of 740 kg/m³ that is about 50 % harder than oak on the Janka scale (around 7,560 N against 4,980 N).

The assembly matters as much as the material. Our tables and benches are bolted, not screwed, and that changes life for whoever manages them: a damaged top can be replaced without touching the frames, the stainless steel bolts are tightened a quarter turn after the first season, and the table can be dismantled to be stored or moved from one site to another. Graffiti or carving comes off with sanding, as on the rest of the furniture — see “Screws and fixings for robinia”.

Solid robinia picnic table with bolted cross-braced frame, top and seats in heavy sections

Solid robinia picnic table: top and seats in heavy sections, cross-braced frame assembled with through-bolts — the heads are visible on the rail. This is what allows a single top to be replaced, the bolts to be tightened a quarter turn after the first season, and the table to be dismantled and moved.

How does this furniture age, and what does its maintenance cost?

Within one to three years robinia takes on a silver-grey patina that takes nothing away from its durability — see “Greying and maintenance of robinia”. No product needs renewing: cleaning with soapy water is a matter of appearance, not preservation.

A scratched, carved or graffitied surface comes back with sanding: beneath the one to two millimetres removed, the wood is identical and its durability intact, because the resistance of the heartwood — the core wood — comes from compounds spread throughout its mass. A scratched composite board cannot be repaired, and a powder-coated section — stove-painted — needs repainting. Finally, parts can be replaced one at a time, as the stainless steel bolts come undone.

Robinia end-grain wood paver surfacing in a public space, weathered timber — End-grain wood paving: the surface greys and scratches, then comes back with sanding — the resistance of the heartwood does not depend on the state of the surface.

Over fifteen years of service	Untreated robinia	Pressure-treated pine, use class 4
Service life in ground contact	around 30 years	around 10 years
Preservative to renew	none	cuts and machined surfaces re-treated
Graffitied or scratched surface	local sanding, identical wood beneath	local sanding, impregnated sapwood at the surface
End of life	untreated wood, can be used as firewood	treated wood waste, dedicated disposal route

How is robinia installed in public spaces?

Installation determines service life more than the species does. A post set in concrete gets a sloping concrete collar, never a hollow that would hold water at its foot; a post base — the metal part that connects the wood to the slab — raises the post a few centimetres and is preferable on a slab or on asphalt.

Robinia is an acidic timber, with a pH of around 4.5: stainless steel fixings are essential, in A4 grade by the sea, and pre-drilling is always required — see “Screws and fixings for robinia”. Anti-theft fixings are chosen in the same grade. On furniture people touch, the edges must be broken, chamfered or rounded, and the surfaces sanded: otherwise such a dense timber produces splinters.

What can be supplied in support of a public tender bid?

Acacia Bois provides the FSC® C153588 certificate and the SGSCH-COC-011793 chain-of-custody certificate — which follows the wood from the forest to the customer —, Romanian forest traceability from the SUMAL system, EUDR documentation, the ISO 9001:2015 certificate and actual transport data, from which a consultancy can build its own environmental calculation.

When it comes to drafting the tender specification, buyers' practice is well established. In the EU, Directive 2014/24/EU allows buyers to specify performance and requires “or equivalent” wording: a technical specification may not name a brand, an origin or a process that would favour one supplier, but it may be written by reference to standards or in terms of performance. In the UK, the Procurement Act 2023 follows the same logic. Requiring natural durability class 1-2 to EN 350 and use in class 4 without chemical treatment therefore describes a performance that several species can achieve. This note describes a practice; it is not legal advice.

Where is robinia not the right choice?

The purchase price of robinia remains higher than that of use class 4 pressure-treated pine, for both raw material and finished products: the argument only holds in a whole-life cost calculation. Long straight lengths are rare, as robinia grows crooked on trees harvested at 25-30 years old, 15 to 30 cm in diameter; beyond 4 m in sawn section, you have to go to finger-jointed timber, short pieces glued end to end.

The variation in appearance is real: colour, grain, knots and surface checks — shrinkage checks with no structural consequence — differ from one piece to the next. For twenty strictly identical benches it gets in the way, and the only answer is stricter grading, and therefore a higher price. Composite or powder-coated metal offer a uniformity that robinia will never match.

Key points

· Robinia reaches durability class 1-2 (EN 350) and use class 4 (EN 335) without chemical treatment: no product to renew.

· Cost per year of service is the right unit for purchasing: around 30 years in ground contact against about ten for use class 4 pressure-treated pine.

· Picnic tables are made in heavy solid sections and bolted: replaceable top, bolts that can be re-tightened, a table that can be dismantled and moved.

· Graffiti or a scratch comes off with sanding, and parts can be replaced one at a time thanks to removable stainless steel bolts.

· A tender specification can require durability 1-2 (EN 350) and use in class 4 without treatment: that is a performance, not a brand.

· Limits: higher price than pressure-treated pine, long straight lengths rare, variation in appearance.

Frequently asked questions

Does robinia street furniture stand up to graffiti and vandalism?

Robinia takes knocks well: its density of around 740 kg/m³ stops a seat from denting under a kick or a skateboard. As for graffiti, bare wood absorbs paint like any porous surface, but the repair is simple: local sanding removes the paint and one to two millimetres of material, and the wood underneath keeps the same durability, since no surface treatment plays any part in its protection.

Should an annual maintenance budget be set aside for robinia furniture?

No preservation maintenance is needed: robinia meets use class 4 (EN 335) without treatment, so there is neither preservative nor finish to renew. The useful budget line covers something else: an annual visual check of the fixings, re-tightening of the bolts after the first season, and cleaning when footfall justifies it. Applying a penetrating oil to keep the honey colour is an aesthetic choice, to be redone every two to three years, not a technical requirement.

Can robinia be specified in a tender without discriminating against bidders?

In the EU, Directive 2014/24/EU prohibits technical specifications that name a brand, an origin or a manufacturing process that would favour or exclude suppliers, unless the need cannot otherwise be described, and then only with the words “or equivalent”. It does, on the other hand, allow specifications to be written by reference to standards or in terms of performance. In the UK, the Procurement Act 2023 follows the same logic. Describing natural durability class 1-2 to EN 350 and use in class 4 without chemical treatment follows this second route. It is standard purchasing practice, not legal advice.

Can we get identical batches and replacement parts years later?

Yes: our sawmill in Teiu, Hunedoara County (Romania), produces to order, not from stock. A batch comes from the same lot of logs, with the same sections, and the drawing stays in production: a slat, a leg or a planter board can be reordered identically five or eight years after installation. One caveat, though: the colour of a new piece will not match that of a set that has already turned grey, and the difference takes one to three years to disappear.