Corten steel: the complete guide

Corten steel is a low-alloy steel designed to withstand the weather without paint or galvanising. Exposed to rain, air and sun, it develops a dense, tightly bonded oxide patina of deep orange-brown that greatly slows the progress of corrosion into the core of the metal. Rust eats away at ordinary steel; the Corten patina protects it. The whole paradox of this material, and all of its beauty, lies in that reversal.

Corten goes by several names. COR-TEN is the historic trademark registered by the American steelmaker US Steel; it gave the material its everyday name, written Corten steel, Cor-Ten steel or simply Corten. Engineers call it weathering steel, and sometimes self-weathering or self-protecting steel. The name itself holds two promises: CORrosion resistance and TENsile strength, the steel’s resistance to being pulled apart.

In Europe, Corten steel falls under the EN 10025-5 standard, which governs structural steels with improved atmospheric corrosion resistance. The most widely used grades are S355J0W and S355J2W, close to COR-TEN B, along with their phosphorus-enriched variants, S355J0WP and S355J2WP, close to COR-TEN A. In the United States, the ASTM A242 and A588 standards designate steels of the same family: A242 corresponds to COR-TEN A, A588 to COR-TEN B.

Its composition explains everything. The base is that of a structural steel, iron and a little carbon, to which small amounts of copper, chromium, nickel, phosphorus and silicon are added. These alloying elements change the very nature of the rust: instead of a porous layer that flakes away and keeps laying the metal bare, they encourage a thin, compact oxide bonded to the surface, which water and oxygen find harder and harder to pass through.

This is what sets Corten steel apart from ordinary steel. Mild steel left outdoors has to be painted, galvanised or powder coated, or it will eventually corrode right through. Corten needs no coating at all: its protection comes from its own surface, and its colour is not paint but a record of its exposure to the elements. For a piece of Corten steel furniture, that honesty of material is already a luxury.

THE DEFINITION IN THE STANDARD

The EN 10025-5 standard (NF EN 10025-5:2005, the French transposition of EN 10025-5:2004, as cited by the French Wikipedia) defines weathering steel as a steel to which phosphorus, copper, chromium, nickel or molybdenum have been added to increase its resistance to atmospheric corrosion, through a ‘self-protecting layer of oxides on the base metal’ formed under the influence of atmospheric conditions.

What is Corten steel used for? Edging, planters, fire pits, façades

In the garden, Corten steel serves first as edging: a blade of sheet steel that separates a bed from a path and holds back the soil without buckling. Then come planters and bottomless planters, fire pits and fire tables, fountains, screens and decorative walls. Beyond the garden, it clads façades, carries bridges, lines major roads and serves sculpture. Its warm tones sit naturally with planting, and it outlasts timber in a suitable setting. Nine ways to use it are gathered in Corten steel garden ideas.

Planting brings structure, water creates calm and fire draws people together. Explore Corten steel pieces by the role they will play in your garden.

Start with the purpose: planting, water, fire, log storage or screening. Product pages list dimensions, options and equipment. Our material guide explains weathering steel and its patina.

The composition of Corten steel comes down to a few tenths of a percent. On a base of iron and carbon identical to that of a structural steel, EN 10025-5 sets ranges for copper, chromium, nickel and, for the grades known as WP, phosphorus. These additions, minute at the scale of a sheet, decide the nature of the rust and the hold of the Corten patina. The table gathers the ranges of the four most common grades, maximum values unless a range is shown; they describe the standard, not a Cortenys piece, and the exact composition of a sheet appears on its inspection certificate.

The role of each alloying element

• ·Copper and phosphorus encourage a thin, adherent oxide in place of the porous rust of ordinary steel.
• ·Chromium and nickel densify that layer and help it stay stable through the wet and dry cycles.
• ·Silicon and manganese are those of any structural steel; carbon stays low, which preserves weldability and folding.
• ·Vanadium, which thyssenkrupp lists only for COR-TEN B, is a common micro-alloying element in structural steels.

Corten A or Corten B: what is the difference?

Corten A corresponds to the WP type of the standard, S355J0WP and S355J2WP: a phosphorus content of 0.06 to 0.15 %, flat products of small thickness, an even patina sought in architecture, and particular care in welding. Corten B corresponds to the W type, S355J0W and S355J2W: ordinary phosphorus, guaranteed impact toughness at 0 °C (J0) or at -20 °C (J2, K2), a calling for structures and loaded works. Both weather in the same way; the letter says nothing about the colour. A common confusion swaps the two: it is the WP type, and so Corten A, that is enriched with phosphorus.

The history of Corten steel begins in the United States in 1933. US Steel developed it for railway wagons: a steel able to face rain and frost without maintenance. For nearly three decades, Corten remained an engineer’s metal, devoted to rolling stock and industrial structures. It was asked to be tough; nobody yet thought of looking at it.

In the early 1960s, architects seized on it. The John Deere headquarters, designed by Eero Saarinen and completed in 1964 in Moline, Illinois, was one of the first buildings to leave the metal bare: rust became the façade. Sculptors followed. Chicago’s monumental Picasso, unveiled in 1967, is made of COR-TEN; Richard Serra made weathering steel his material of choice; Antony Gormley’s Angel of the North has stood on a hill in Gateshead, England, since 1998. In France, the Musée Soulages in Rodez, designed by RCR Arquitectes, clads its volumes in Corten steel.

From railway lines to museums, Corten won over architecture and art. What remained was to bring it into the garden and the home with the same exacting standards. Too often, Corten steel garden furniture still amounts to little more than a folded sheet, delivered grey and left to the whims of the seasons. Cortenys chose the opposite course: treating Corten as a noble material, with the design, precision and finishing expected of luxury furniture. A different idea of Corten steel furniture.

Corten steel grows more beautiful with age, provided it can breathe. Its patina builds up in cycles: rain or dew moistens the surface, sun and wind dry it, and each alternation tightens the oxide layer a little further. It is this succession of wetting and drying that makes the patina protective. Corten kept permanently damp, buried or sitting in standing water never forms that stable layer, and goes on corroding.

In the open air, raw Corten steel moves from the grey of bare steel to a vivid orange within a few days or weeks, then darkens through rust and burnt sienna to a deep, velvety matt brown. The patina reaches equilibrium within a few months to a few years, depending on the climate, the orientation and how often it rains: a garden in a maritime climate matures it faster than a sheltered patio under dry skies.

Once stabilised, the Corten patina never stops living. It heals over a scratch of its own accord, shifts in tone with the seasons and slowly gains in depth. That is why Corten structures exposed for several decades are still admired today. A piece in Corten steel never goes out of fashion: it weathers, wearing the passing years rather than enduring them.

Does Corten steel really rust?

Yes, and that is its strength. The Corten patina is rust, but a stable, thin rust bonded to the metal, which protects the core of the steel instead of eating it away. As long as the piece can dry between two showers, this layer renews itself and closes over small scratches. It therefore needs neither paint nor rust treatment.

This protection has one condition, which the engineering guides repeat: the alternation of wet and dry. A surface that stays wet forms no adherent patina and corrodes at the rate of ordinary steel; a patina damaged again and again, by knocks or harsh cleaning, ends up shortening the life of the piece.

Can you speed up the Corten patina?

Many pages promise a patina in a few hours, with salt water, vinegar or an activator. The French Wikipedia points out that a rust accelerator often works against the long-term stabilisation of the material, and the chlorides of salt water are exactly what the patina fears. The healthy accelerator is nature’s own: frank cycles of wetting and drying, rain rather than shelter. At Cortenys the question does not arise: the signature patina is initiated and guided in the workshop, then inspected piece by piece before delivery. And never a pressure washer on a young patina.

A guide worthy of the name must also address the limitations. Corten steel has its own, and they are well known. It is precisely in the way they are handled that an exceptional piece stands apart from a mere sheet of rusted steel. Here are the disadvantages of Corten, and how the House answers each one.

Each limit has its chapter: sea, pool and winter, wood, stone and other metals, maintenance. The protective varnish answers most of them; it greatly reduces run-off without ruling it out, so a light or porous floor is still best protected.

The price of Corten steel is read at two levels that have almost nothing in common: raw sheet, sold by the square metre or by the kilo by steel suppliers, and the finished piece, which pays for the design, the fabrication and the patina. Here are both reference points.

Price of raw Corten sheet per m² (dated readings)

Prices read on 27 September 2026 on the websites of three French steel suppliers and cutting services, for bare sheet. They move with the price of steel, the format and the quantity: they set an order of magnitude, nothing more.

From sheet to finished piece: what you pay for

The price of Corten steel depends on the thickness of the sheet, the dimensions, the complexity of the cutting, folding and welding, the patina finish, any varnish and any bespoke work. Varnish adds a step, not a guarantee: even varnished, Corten steel can still mark a pale floor. Raw sheet sold by the square metre has nothing in common with a finished piece of furniture: design, fabrication, applied patina and inspection make up most of its value. The price of each Cortenys piece is shown on its product page or given on request; bespoke work is quoted individually.

Why more expensive than ordinary steel? Copper, chromium and nickel have a price, and the welds call for a matching filler metal. The engineering guides speak of a slightly more expensive steel, whose premium is offset by the absence of a paint system. Our article Corten steel price sets out, item by item, what you pay for; bespoke work is quoted individually, and professionals have a dedicated contact.

Ordinary steel rusts in depth: its rust is porous, flakes away and keeps exposing fresh metal, hence the need to paint or galvanise it. Corten steel, by contrast, forms a compact patina that slows corrosion and does away with any coating. It is also more expensive, and its welds call for a matching filler metal so that the patina stays even.

The difference lies neither in mechanical strength, comparable to that of an ordinary S355 steel, nor in weight, which is identical, but in the chemistry of the surface. Against galvanised steel, stainless steel or aluminium, Corten steel stands apart by a protection born of itself and a colour that is not a coating.

Corten, galvanised steel, stainless steel or aluminium: the comparison

Corten or powder-coated aluminium for garden furniture?

The House offers both materials to the same design. At equal thickness, aluminium is about three times lighter than steel, which counts on a terrace or a balcony. Powder coated in a RAL colour, it keeps a stable colour, never runs onto pale ground and fears neither sea spray nor pool water: it is the House’s answer for the coast and for direct contact with water. Corten steel offers what aluminium does not have: a living patina, a depth that changes with the light, a presence of raw material among planting and stone. The Nereida cascade fountain and the Elio round fountain exist in both versions; planters, fountains, water basins and log stores in aluminium are gathered on the luxury aluminium outdoor furniture page.

Corten steel near the sea

With caution. Sea spray deposits chlorides that prevent the Corten patina from stabilising and keep corrosion going. Right on the coast, the House recommends its powder-coated aluminium pieces, which do not rust. Further back, a varnished piece, rinsed regularly with fresh water, can be considered: we assess it with you, case by case, knowing that even varnished it can still leave rust stains on a pale terrace.

An engineer’s reference point sets the risk: the British guidance advises against weathering steel for bridges within 2 km of the coast, unless the salinity of the air stays below class S2, that is, under 300 mg of chlorides per square metre per day to EN ISO 9223. In a garden, there is no single distance: the prevailing wind, the lie of the land, the height and the vegetation count as much as the metres. Our article Corten steel near the sea helps you place your terrace.

Corten and other metals: galvanic contact

Two different metals in contact, in rainwater, form a battery: that is galvanic corrosion. The civil-engineering guides recommend avoiding connections with galvanically dissimilar components, such as zinc-plated screws or galvanised parts, and specifying weathering-grade bolts. In furniture, stainless steel fasteners are common practice; aluminium is isolated from Corten steel by a gasket or a spacer wherever there is water. At Cortenys, the fasteners and fittings of each model are chosen piece by piece.

Welding Corten steel

Corten steel is welded with the ordinary processes, MIG/MAG or TIG, like a carbon steel. For the weld to weather like the sheet, the filler metal must resemble it: the guides recommend a filler with at least 0.4 % copper, together with other alloying elements, or chosen to EN 1090-2; a single-run fillet weld, up to 8 mm leg length, can be made with an ordinary carbon-manganese filler, dilution being enough to match it. The treatment of the welds at Cortenys is described in the chapter on the craft.

Can you cook on Corten steel?

Corten steel is a structural steel, not a steel designed for food contact, and a patina is not a cooking surface. In a piece designed for cooking, the Corten hearth takes the fire, and the cooking is done on the elements designed for it. The Cortenys Vulcain BBQ pairs a wood fire with a cooking ring. Our fire tables are designed for the flame and for gathering, not as cooking surfaces. The uses of each model are shown on its product page.

Children, pets, hands and clothes

A stabilised patina does not stain clothes: the oxide layer is resistant enough for that, and Corten street furniture proves it every day. A young raw sheet, on the other hand, can mark hands and pale clothing, especially when damp. Cortenys pieces arrive patinated, and varnished they mark far less, though transfer is not ruled out; their edges are crisp and finished. Around a hearth, children and pets keep their distance until the piece has cooled; in full sun, like any dark metal, Corten gets hot.

Very simply. An unvarnished piece needs no paint and no treatment: just remove the leaves, soil or debris that would hold moisture, and rinse with clean water if needed. Avoid wire brushes, as well as abrasive, chlorinated or rust-removing products. A varnished piece is cleaned with a simple wipe of a damp sponge; even varnished, it can still mark a light or porous floor, so protect the floor beneath it.

The maintenance calendar

The table sums up, for a raw piece and for a varnished piece, the steps published in our article Corten steel care.

Should you seal or varnish Corten steel? Raw or varnished

Outdoors, it is not necessary: the patina protects the metal on its own. Varnish is a choice. It fixes the colour, gives it a light satin sheen and greatly reduces marks on the ground without ruling them out: on a pale terrace or beside a swimming pool, we recommend adding small feet, spacers or a drip tray. Indoors, it is mandatory at Cortenys: the protective varnish is applied in the workshop to every piece intended for the home.

Raw, meaning without varnish but always delivered with the Cortenys signature patina, Corten steel keeps on living: its colour deepens and tells the story of your garden’s climate. Varnished, it stays fixed in the state chosen in the workshop, denser, with run-off greatly reduced. Choose raw for a bed, gravel or a lawn; varnished for a pale stone terrace, a poolside or an interior, always with the floor protected, since even varnished Corten steel can still stain it. The protective varnish page details the finish.

At Cortenys, every detail of Corten steel furniture has been rethought: the thickness, the weld, the patina. Sheet thickness is chosen model by model, from 1.5 to 3 mm, always shown on the product page, according to what the piece must carry and the line it must hold, so that volumes stay taut and edges crisp. Welds are treated as part of the design, clean and discreet. Nothing is produced in advance: every piece is made to order, then inspected before it leaves the workshop.

Designed in France and crafted in Europe by a partner manufacturer, our pieces carry no logo, no plate and no signature: the House is recognised by its lines and its patina. Where the market sells sheet metal, Cortenys composes pieces, gathered into two collections: the Classics and the Cortenys Creations. Every piece is guaranteed for two years. Delivery is free, to your door; pieces arrive ready to install, and the House does not provide on-site installation.

From garden to home, Corten at Cortenys takes the form of luxury furniture: Corten steel planters and bottomless planters for open ground, fountains, water walls and water bowls, water basins and reflecting pools, fire pits, fire tables, outdoor fireplaces and a BBQ, log stores, decorative walls, lanterns, light bollards and letterboxes. Lighting, tables and an armchair carry the same design language into the home, where every piece receives the protective varnish; even so, we recommend protecting the floor beneath it.

Architects, landscape designers and interior designers find in Cortenys a partner for bespoke work and Corten steel street furniture: dimensions, thicknesses and finishes are studied project by project. For those who recognise an exceptional piece at first glance, this is Corten as it should always have been.