Do you always worry about your garden ornaments and outdoor sculptures rusting and deteriorating in the process? What if you could use a material that forms rust but protects the structure instead of destroying it? Yes, that kind of metal exists! It’s called Corten steel or weathering steel.
Corten steel is the name for the commonly seen ‘rusted’ steel alloy seen in both modern metal art and architecture. Its surface forms a protective oxide layer when exposed to the weather, keeping the metal strong and protected. This means it has excellent corrosion resistance as well as an attractive appearance.
The protective layer of Corten steel keeps on regenerating over years of exposure to weather. Over time, the steel forms a stable rust-like appearance. This iconic weathered look and rusty orange colouring make it popularly used in outdoor sculptures, metal garden art, rustic planter boxes, rustic garden edging, as well as in bridges and other large structural applications.
Would you like to use Corten steel in your next project? Read on to learn more about Corten steel, its rusting process, the pros and cons of using it, how to maintain it and other useful facts.
What Is Corten Steel?
Corten steel is a type of steel alloy designed to naturally generate a rust-like patina, while creating its own protective outer layer. Corten steel is the shorthand for weathering steel that creates a rust-like look after years of weathering, without the structural weakening associated with rust.
This product was originally designed to help build railroad coal wagons, and its success led to its use for outdoor sculptures and architecture. The rusting or weathering process of Corten steel is what makes it special. It does not prevent rusting, but it forms rust only on its outer surface for protection. The presence of chromium, copper and nickel improves the Corten steel’s weather resistance, allowing the development of a desirable patina.
Corten is known for its superior corrosion resistance (COR) and tensile strength (TEN), two distinct characteristics from which the name is derived. When exposed to weather, it forms a protective oxide layer of rust. The beautiful colour created by the natural rusting of the metal means that no paint has to be used to create rich, earthy looks in the metal that continues to grow every year. In addition, this layer of rust completely protects the raw steel underneath it.
What Is Special About Corten Steel?
When exposed to the environment, Corten steel forms a patina or an outer layer of rust because of oxidation over a long period. Instead of deteriorating the metal, the oxidised dark brown coating acts as a barrier, prevents any deeper rust penetration and protects the metal from further corrosion.
Every time the steel is rained on or endures any moisture, the rust layer thickens. After several years, the rust layer will stabilise and form a natural look that other metals need fake paint and finish to achieve. This barrier means you won’t need to do any upkeep for the outer rusted layer or the steel within, unlike other types of steel which need ongoing maintenance. The rust forming on the surface of Corten steel is a naturally rusted surface that changes in colour and pattern and ripens with age, giving the steel an aesthetically pleasing look. This means that when Corten steel is your material of choice, it makes it very easy to maintain outdoor metal art without deterioration. For that reason, Corten is a popular choice for garden edging, planters and other backyard fixtures.
What Is Corten Steel Made Of?
Corten steel is a copper chromium alloy steel that is added with phosphorus and nickel-molybdenum.
The two common types of Corten steel are Corten A and Corten B. Corten A is lower in carbon, manganese and silicon while being more phosphorus, copper and chromium dense. This composition makes it ideal for aesthetic fascias and outdoor sculptures. Corten B has more carbon and manganese in comparison, and has a lower percentage of phosphorus, making it ideal for heavy and load-bearing structures, commonly seen in the construction industry.
How Thick Is Corten Steel?
The thickness of Corten steel largely varies according to type. Corten A, which is typically produced as a coil or sheet, has a thickness ranging from 1 mm to 12 mm. Corten B, which is commonly produced as a plate, is thicker at about 15-50 mm thickness.
Pros & Cons Of Corten Steel
Corten steel is found around the world in various different applications because it’s extremely versatile. Corten’s unique benefits make it a great choice both functionally for construction, and visually for outdoor metal art and facades.
Although it’s not without its downsides, the sheer amount of Corten steel found in modern architecture and construction shows that the positives often outweigh the negatives.
Pros Of Corten Steel
Using Corten steel has the following advantages:
- Durability – Corten steel is a durable type of metal that can last for decades, depending on where it is and how it’s finished.
- Anti-corrosive Properties – The developing rust layer that forms over the Corten steel will help provide corrosion resistance.
- Highly Resistant To The Weather – The prolonged exposure of Corten steel to harsh environmental and weather results in the formation of rust that acts as a protective coating. It prevents corrosion and deterioration of the material by allowing rust to dry quicker and thicker and then developing a beautiful patina.
- Protective Self-regenerating Surface Layer – The layer protecting the surface develops and continues to regenerate when subjected to the weather.
- Distinct Rust-like Appearance That’s Great For Aesthetics – Corten steel or weathering steel often blends well with the environment, and its appearance even improves with time. Its distinct appearance makes it ideal for many types of sculptures, architecture, or landscaping work.
- Low Maintenance Requirement – The rust formation seals the surface and creates a protective layer. It also reduces the amount of glare that’s common on standard metals. As a result, the amount of maintenance needed becomes reduced. You only need to clean and inspect Corten steel products or structures. Cleaning means rinsing the rusted surface with water to remove any natural debris or contamination.
- Cost-effectiveness – Corten steel may be more expensive than mild or ordinary steel to initially purchase, but you will spend less money on maintaining it; making it more cost effective in the long run.
- Environmentally Friendly – Corten steel is an environment-friendly option that’s sustainable and recyclable.
Cons Of Corten Steel
Below are the drawbacks to using Corten steel.
- Retention Traps – The disadvantage of using Corten steel or weathering steel is that it’s not 100% rustproof. If used in buildings and water accumulates in its pockets, these areas may have higher corrosion rates because continuous damp or wet conditions prevent the oxides to crystallise. The potential to trap moisture means you should be careful how you hang metal wall art outdoors.
- Staining – The initial surface weathering of Corten steel may cause rust staining on nearby surfaces. This can be avoided by using designs that drain loose rust products onto neighbouring surfaces. Choosing the right metal art design will help mitigate this risk.
- Compatibility With Climates – Corten steel is not compatible with all climates. It is sensitive to humid climates. In these areas, the protective patina may not form properly, and the steel may continue to corrode.
- Welding Technique – Welding Corten steel requires similar precautions as when welding mild steel. It can be welded manually and mechanically, but the difference is the need for a special filler material to produce the weathering steel weld in some cases. To get identical mechanical properties in the weld and in the base material, suitable welding consumables and welding conditions must be used.
Cost of Corten Steel FAQs
Corten steel is more expensive than common steel. Its cost depends on different factors, like the dimensions of what you want to buy.
How Much Does Corten Steel Cost?
The cost of Corten steel on average is between $35 and $70 per square metre. However, the cost of Corten steel depends on a variety of factors, including the amount, length and weight of the steel you’re buying. The greater the dimensions are, the higher the price is.
Is Corten Steel Expensive?
Yes, Corten steel is more expensive than other common grades of steel. Depending on the application, pieces fabricated from Corten steel can cost between 50% and 300% more than mild steel. However, the unique appearance of Corten means many people are willing to pay a premium to get the aesthetic they prefer.
If Corten steel is out of your budget, there are some Corten steel alternatives that may also be suitable for your project.
Corten Steel & Rusting FAQs
How Long Does Corten Steel Take To Rust?
Under normal conditions, and if the surface is alternately wet and dry, the patina forms and matures within 18-36 months. Some weathering steel can even form a patina between 6 months and 1 year. However, the entire process can take between 4-10 years.
Patina forms consistently when the Corten steel is subjected to alternating wet and dry periods. The rusting or weathering process depends on the aggressiveness of the environment into which the Corten steel is placed and the frequency of the wet and dry cycle.
How Can I Speed Up Corten Steel Rusting?
The more frequent the wet and dry cycle is, the quicker Corten steel will rust. To quicken its natural ageing or rusting process, more frequent wet and dry cycles are needed. Spraying saltwater or a mixture of salt solutions mixed with vinegar and peroxide onto Corten steel also hastens the process. It should then be allowed to dry, and the process should be repeated until rust forms.
Does Corten Steel Stain Concrete?
Yes, Corten steel can stain concrete. The carbon runoff from its surface, particularly during the early stage of weathering, can stain concrete, stucco, paint and stone surfaces. It takes a few years of exposure to stabilise the material’s rust condition. After the initial reactive period, the steel will cure, mature and self-seal with little to no carbon runoff. To avoid staining altogether, consider alternatives to Corten steel instead.
Can You Keep Corten Steel From Rusting?
Corten steel oxidation can be prevented with an anti-rust coating or by sealing it to keep the atmosphere from contacting the metal surface. However, since its unique rusting process is the reason for choosing Corten steel, it is more cost-effective to opt for an alternative if this isn’t desired.
Sealing & Maintaining Corten Steel
Sealing prevents further deterioration of Corten steel. When sealing metal art, it must receive a minimum of one or two coats, depending on factors like its location and thickness. The Corten steel changes colour and appears darker during each application. Once it’s sealed, it won’t weather anymore.
Can Corten Steel Be Sealed?
The rusting process seals the Corten steel. However, to prevent further corrosion and rust stains from getting on other surfaces, Corten steel can be sealed using polyurethane or Everbrite. This gives it a darker, more durable finish. Polyurethane is a common type of metal sealant. It’s available in both a semi-solid form for joint sealing and in a liquid form for sealing large surfaces of metal.
How Do You Maintain Corten Steel?
Corten steel products need little to no maintenance. You can clean Corten with water to remove debris or prevent further corrosion with a sealant. To prolong their life, Cortel steel products should be in an area where they can quickly dry after rain.
There’s also no treatment needed for Corten steel products. New Corten steel comes without its rust patina. Weathering steel pieces will form the protective rust layer based on their environment. If you place it outside, rust formation will start after a few weeks to months.
Learn more about how to maintain outdoor metal art.
Corten Steel & The Environment FAQs
Corten steel is not only economical and long-lasting. It’s also an environmentally-friendly material.
Is Corten Steel Sustainable?
Being durable, Corten steel is a sustainable choice. It requires relatively low energy levels during its manufacture. Corten also requires little to no maintenance, and its corrosion resistance performance is 8x higher than ordinary steel. This means that you can use it 8x longer than a common steel, without the need to paint it.
The average lifespan of Corten steel is over 20 years, and it can last for many decades. With the length of time it can be used for a project, Corten steel can reduce the need for raw materials, as well as other expenses like construction, painting and maintenance.
Is Corten Steel Recyclable?
Yes, Corten steel is easily recyclable. It is made from pre- and post-consumer recycled steel and is also recyclable itself. Once its useful life ends, you can take it to any workshop or factory for casting metals to be repurposed. The recoverable percentage when recycling steel is close to 100% and it does not degrade when recycled. Reusing it minimises waste and is environmentally friendly.
Is Corten Steel Safe For Vegetables?
Yes, Corten steel is safe for vegetables. You can safely grow vegetables in Corten planters by lining the planters’ interior with food-grade waterproofing coats or materials.
Among Australian Corten steel suppliers, Corten steel planters come ready to use. You may also have them fabricated and installed in your garden. Corten steel is an ideal garden material because it can last for decades. It can last long even in dirt and soil with next to no maintenance required.
Its natural earthy colours are also perfect in a vegetable garden, providing contrast to the green vegetable colour. You can fit Corten steel even in tiny spaces because it’s thin. Shaping it in any way you want is possible, since steel is easy to laser cut and fabricate.
Where Can I Buy Corten Steel In Australia?
You can buy Corten steel from various steel suppliers around Australia. You can get residential and commercial metal art, property signs and privacy screens that are made of Corten steel from Kanyana Engineering in Western Australia.
Corten Steel Metal Art
Looking for stunning laser cut Corten steel for your indoor or outdoor spaces? Kanyana Engineering are the local experts in custom metal art, creating stunning and unique designs to suit every home. We also create custom commercial metal art for businesses and organisations. Choose from a range of wall art and fence topper designs, or request something completely unique from our talented team.
View our metal art designs here or contact Kanyana Engineering to find out more.
This article is published in good faith and for general informational purposes only. Kanyana Engineering does not make any warranties about the ongoing completeness and reliability of this information. Always seek specific advice on your metal fabrication project to ensure all variables are taken into consideration.
Graham Dawe is the Managing Director and Works Manager of Kanyana Engineering. With decades of experience in the metal fabrication industry, he is dedicated to keeping Kanyana at the forefront of the sector’s technological growth. Looking beyond the process itself to holistic, integrated CAD, CAM and MRP solutions, Graham believes Australian manufacturing has an enduring place on the global stage. In Kanyana Engineering’s state-of-the-art workshop in Mandurah, WA, Graham delivers an exceptional standard of work for commercial, industrial and government clients alike.