CORTEN STEEL

for garden objects

High quality special steel

for garden objects

In Germany, the term Corten steel*) is used to describe weather-resistant structural steel on whose surface a barrier layer is continuously formed under the influence of weathering. This protects the components from further corrosion and provides the characteristic patina in earthy and warm tones. Corten steel has a longer than average life, does not require painting and is fully recyclable. We use only the particularly high quality steel grade S355J2W+N, material number 1.8965, which can also be bent and welded with the right filler metal.

*) The designation COR-TEN steel was composed of the first syllable COR for CORrosion Resistance and the second syllable for TENsile strength. COR-TEN steel was filed for patent in America in 1932. There are very many different types of weather-resistant structural steel in the world.

08A_117_KU_living_gardens_metal_Corten_steel_TERRESTA_Slider
Corten steel plant trough with typical rust red coloration

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CORTENSTAHL

Corten steel berosten

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User information METAL

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Further literature and references

Areas of application of corten steel

Corten steel is used in a very wide range of applications: for bridge structures, facades or guardrails. Popular examples are the guard rails on Italian highways. In recent years, corten steel is increasingly used for metal garden objects. The characteristic patina develops a certain life of its own and changes the structures and colors again and again. Last but not least, this property makes corten steel an ideal building material in modern garden and landscape design.

For incomparable quality: delivery condition "mill finish without mill skin

Commercially available corten steel sheet has a rolled skin on the surface due to the manufacturing process. This consists of a firmly adhering, blue-black layer of very hard iron oxides. The rolled skin is brittle and delays the formation of the stainless barrier layer desired in corten steel. In the first few months of weathering, the rolled skin then peels off bit by bit, revealing the “real” bare steel surface. The flaking rust-brown rolled skin is disturbing and unsightly.
Therefore, we practically process only the particularly high-quality Corten steel, where the rolled skin is pickled directly after production – before processing. This is more costly in terms of procurement and production, but you can simply see the high quality of our products thanks to the optimum primary products. Not only is the flaking of the rolled skin completely eliminated, but also the accuracy of laser cutting, bending and welding is much higher than for simple material with the hard and brittle rolled skin.

Patina development

During the production and processing of the raw steel panels on the surface is not yet formed patina. This develops only through natural weather conditions. The formation of the visually appealing surface begins after 2 to 3 weeks and is completed only after 1.5 to 3 years. Important in the formation of the barrier layer is the alternation between wet and dry weather. If there are surface areas that are not exposed to this weathering, the living patina of rust will not form there. To find out how to accelerate surface russeting thanks to our SUPER-ROST process, click here: SUPER-ROST process with SUPER-ROST pad

SUPER-ROST-Pad for fast rusting of corten steel surfaces
SUPER-ROST pad for fast pre-rusting

Color differences during pre-rusting

It is hard to believe, but perception cannot be fooled: Depending on the weather and environmental influences, a different initial rust coloration develops on the surface – with the same material from an identical production batch.
The main factors influencing rust coloration are temperature and relative humidity. Lower temperatures and high humidity result in a darker color. Different colorations after the first bursting become more and more similar as the weathering of the objects progresses. This different coloring is therefore not a defect or reason for complaint.

Corten steel surfaces in different shades of color

Black spots on corten steel

In the absence of air, the still young, rusted surface can turn black, for example, if it is packed for transport with a tight-fitting film. This coloration recedes after a few days under natural weathering, so it is not a defect or reason for complaint.

Corten steel_black_stains_garden_metal
Screen wall on which black spots have formed under foil.

Temporary black discoloration can also occur if dead leaves collect on the surface or if planting touches the corten steel surface over a long period of time. Again, after removing the leaves, the natural weathering will soon restore the familiar rusty surface.

Black discoloration on corten steel
Black spots due to plant remains

Impressions from vacuum cup on corten steel

When the raw boards are processed, they are gripped automatically at several production stations with the aid of vacuum suction cups and transported for further processing. Impressions of this can become visible after the first touching – sometimes less, sometimes very clearly.
These imprints, also called “crop circles” in expert circles, are caused by the fact that during the application of the SUPER ROST agent, the surface is disturbed by minimal residual particles adhering to the suckers. The imprint becomes visible only after formation of the first red rust patina after 12 h to 24 h. However, with natural weathering, the imprint disappears again. To speed up the process, the affected areas can be mechanically abraded a little and russetted again.

Attention sign

Note: The appearance of impressions caused by vacuum cups on the pre-rusted surface does not entitle the customer to make a complaint.

Sucker imprints (= crop circles) after the first rusting of Corten steel.
Sucker prints (= crop circles) after the first berosten
Corten steel rusted through when installed incorrectly
Normal steel instead of Corten steel rusts through quickly outdoors.

Corten steel classified as ecological material

Weatherproof structural steel can be classified as an ecological material. It has an above-average service life, does not require painting and is fully recyclable. Corten steel has minimal amounts (less than 1%) of high-grade copper and chromium firmly bound into the metal, making the material – similar to stainless steel – almost infinitely durable and preventing rust-through.

Attention sign

Note: Decorative elements or cheap planters are often offered in the hardware store with the designation “Edelrostoptik”. Behind it, as a rule, is normal steel. It can rust through after only a few months in the garden and become a danger to pets and insects.

Is corten steel or structural steel harmful to health in the garden?

Time and again, the question arises as to whether weather-resistant structural steel is harmful to health due to the alloying components copper and nickel. If you understand how corten steel “works”, you will see that the concerns are unfounded. The corten steel rusts and then forms a solid barrier layer with the alloy components. These therefore do not enter the environment. Therefore, corten steel is as harmless as stainless steel, which is used, for example, in the kitchen and hospital.
Problematic is the use of ordinary and cheap structural steel in the garden, which is often used for decorative objects from the hardware store. The structural steel gradually dissolves. In the process, the alloying components copper and nickel are also released and can be ingested, for example, by insects, pets and also humans. The dissolved oxidation products of steel (=the rust), on the other hand, are harmless and act as a fertilizer.

Removal of deposits on patio slabs/natural stone

Rusty deposits, e.g. caused by drain water, can be removed more or less successfully with a suitable rust remover. The cleaning success essentially depends on the following factors: Base material, frequency and quality of cleaning, and suitability of the cleaning agent.

Cleaners based on phosphoric acid can be used with good success on acid-resistant floor coverings. In the case of slight contamination, household remedies such as common salt in combination with citric acid powder (= ascorbic acid) and water are also suitable. Do not use acidic cleaners on concrete-bound floor coverings; only tannin-based cleaners should be used. Since the surface turns reddish-purple during treatment, it is essential to ensure proper application to avoid consequential damage. In all cases, test the effect of the cleaner on the surface using a small sample area!

Corten steel sealing

To reduce rusty deposits and “protect” corten steel, there is the possibility of sealing the rusty surface, once the desired stainless surface with the appropriate protective layer has formed. The sealant acts like a classic layer of varnish and must be repainted again and again as needed (e.g. annually). For more information on rust sealing, see ROST-PROTECT®.

Corten steel with ROST-Protect, sealant
Sealed corten steel at a water bowl AQUA BOWL

Keep snails away with corten steel

Areas with corten steel forms an almost insurmountable obstacle for snails. The reason: corten steel contains a small amount of copper (<1%). If the snail creeps over the corten steel, the snail slime oxidizes the copper. This creates an irritating substance that causes the snail to immediately turn away. For safety from undermining by snails, the tapes should be tied at least 10 cm deep in the soil.

Corten steel protects from snails
Effective slug barrier: slugs avoid corten steel.

Tender text for GaLaBau, for landscape architects and planners

” Flat steel rolled. Made of weather-resistant structural steel/Corten steel Corten B ASTM A 588, grade S355J2W+N. Material no. 1.8965 according to EN 10025-5 with acceptance test certificate. Surface optically pre-rusted on the visible sides.”

Sheets and blanks

If you need blanks, sheet metal cuttings, blanks or even individual sheets in corten steel – also optically pre-rusted – we can offer these very cost-effectively in many cases, as we buy corten steel in large quantities. Even smaller steel distributors and many locksmiths buy their corten steel requirements from us. Ask also for corten steel without rolled skin. The material is produced in by the major steel producers exclusively for Gartenmetall®. You can find a price list and more information here: SHEET METAL BLANKS

Everything important at a glance.

CORTENSTAHL

Corten steel berosten

Information material

User information METAL

Tender For base material

Further literature and references