How to Treat and Protect Corten Steel?

Corten steel — also known as weathering steel — has become a favorite material among architects, designers, landscapers, and metal artists. Its distinctive warm orange-brown patina, industrial look, and exceptional resistance to atmospheric corrosion make it both functional and aesthetic. Yet, despite its durability, Corten steel requires proper treatment and protection to develop its patina correctly and to ensure long-lasting beauty and performance.

In this article, we’ll explain what Corten steel is, why and how to treat it properly, and how to protect it from unwanted damage or stains. We’ll also share professional recommendations from Corten+, a leading provider of Corten steel treatment products, including our acid-free rust accelerator, descaler, degreaser, and protective sealer.

What Is Corten Steel?

Corten steel (short for CORrosion resistance and TENsile strength) is a special type of steel designed to form a stable rust-like appearance after exposure to the weather. Unlike ordinary steel, which continues to corrode until it disintegrates, Corten steel’s surface oxidation creates a protective layer that prevents deeper corrosion.

This protective layer, called patina, evolves over time and gives Corten steel its signature earthy orange-brown color. It is widely used in architecture, garden design, public art, and modern construction for its natural aesthetics and longevity.

However, achieving and maintaining this patina correctly requires proper preparation, controlled oxidation, and protection — three steps that make all the difference between a beautiful, lasting result and premature corrosion or surface damage.

Step 1: Preparing the Surface

Before beginning the oxidation process, the steel surface must be properly prepared. This preparation depends on whether the Corten steel is hot-rolled or cold-rolled.

Understanding Hot-Rolled vs. Cold-Rolled Corten Steel

The difference lies mainly in the manufacturing process and thickness:

Cold-rolled Corten steel is generally less than 2.5 mm thick and has a smoother finish. It’s often used for decorative panels, interior designs, and thin metal sheets.
Hot-rolled Corten steel is typically more than 2.5 mm thick and has a rougher, darker surface. It’s used in structural applications, planters, sculptures, and outdoor installations.

⚠️ Important: This thickness rule is only a guideline. To be certain whether your steel is hot-rolled or cold-rolled, always confirm the rolling process with your supplier.

Each type requires a different treatment before rusting can begin.

If Your Corten Steel Is Hot-Rolled: Remove the Mill Scale

Hot-rolled Corten steel is covered with a dark, bluish layer called mill scale — a byproduct of the manufacturing process. This layer prevents the steel from rusting evenly, which means it must be removed before applying any rust accelerator.

At Corten+, we recommend sandblasting (or grit blasting) the surface. This mechanical method removes the mill scale thoroughly, leaving a clean, slightly rough texture that’s perfect for oxidation.

However, if you don’t have access to a sandblasting machine, we offer a powerful alternative: our Corten+ Descaler (also known as Descaler in English). This product is specially formulated to chemically remove the mill scale safely and effectively.

How to Use the Corten+ Descaler

Spray the product evenly on the surface of the steel.
Let it react for the recommended time (see instructions on the bottle).
Rinse the surface thoroughly with water to neutralize and remove residues.

Because the Corten+ Descaler is a strong product, rinsing is essential to ensure the steel is perfectly clean and ready for the next step.

If Your Corten Steel Is Cold-Rolled: Degrease the Surface

Cold-rolled Corten steel doesn’t have a mill scale, but it comes with a protective grease layer applied during manufacturing to prevent premature rusting. This grease is extremely resistant and cannot be removed with ordinary household degreasers.

To ensure proper oxidation, you must use a special degreaser designed for Corten steel — such as the Corten+ Degreaser.

Why a Specialized Degreaser Is Necessary

The grease used on cold-rolled steel is highly tenacious because it protects the steel during storage and transport. Regular degreasers often fail to remove it completely, leaving behind residues that block oxidation and cause uneven rusting.

The Corten+ Degreaser is formulated to dissolve this type of industrial grease completely, leaving the surface perfectly clean and ready for rust acceleration.

Application Steps

Spray or apply the Corten+ Degreaser evenly on the surface.
Let it act for several minutes according to the product instructions.
Rinse with clean water and allow the steel to dry.

Once this cleaning step is done, your Corten steel is now ready for oxidation.

Step 2: Accelerating the Rusting (Oxidation) Process

This step is where most mistakes happen. Many people try to speed up the rusting process using acid-based products, thinking it will help Corten steel develop its patina faster. While acids do create rust quickly, they also destroy the protective properties of Corten steel — leading to uncontrolled corrosion, perforation, and long-term damage.

The Problem with Acid-Based Rust Accelerators

Acid attacks the steel surface, initiating a corrosion process that never stops. Even if the steel looks rusted on the surface, the acid continues to penetrate and degrade the metal underneath. Over time, this can lead to holes, structural weakness, and irreversible damage.

Moreover, acid-based treatments are dangerous to handle, requiring protective equipment and often a neutralizing “stop bath” afterward to halt the chemical reaction. This adds complexity, cost, and risk to the process.

Why Choose the Corten+ Rust Accelerator

This is where Corten+ makes a real difference. Our Corten+ Rust Accelerator is 100% acid-free. It triggers a natural oxidation process without damaging the steel or endangering the user.

Key Advantages:

Acid-free and non-corrosive: It protects the integrity of the metal.
Safe for users: No toxic fumes or corrosive reactions.
No need for a stop bath: The process is self-limiting and controlled.
Cost-effective: Because you don’t need multiple complementary products, the Corten+ system is up to three times cheaper than acid-based alternatives.
Fast and uniform results: It promotes even rusting across the surface.

The Corten+ Rust Accelerator mimics natural weathering conditions — but in just a few hours instead of several months.

How to Apply the Corten+ Rust Accelerator

Preparation: Make sure the surface is completely clean and dry after descaling or degreasing.
Application: Spray the Rust Accelerator evenly across the surface. Avoid applying in direct sunlight or in very windy conditions.
Reaction: Within a few hours, the surface will begin to turn orange as the oxidation starts.
Observation: Over the next 24–48 hours, the patina develops into a rich, natural rust tone.

Depending on your desired shade (light orange, deep orange, or darker brown), you can apply additional coats until the desired color is reached.

Because the product contains no acid, you don’t have to neutralize or rinse it afterward. The oxidation process stops naturally when the metal surface stabilizes.

Comparing Acid-Based vs. Corten+ Oxidation Systems

Feature	Acid-Based Accelerators	Corten+ Rust Accelerator
Chemical Composition	Contains acids	100% acid-free
Corrosion Risk	High — corrosion continues over time	None — oxidation is self-limiting
Safety for Users	Dangerous, toxic fumes	Safe, non-toxic
Requires Stop Bath	Yes	No
Long-Term Effect	Damages steel	Protects steel
Cost	High (requires multiple products)	Lower (single-step solution)
Appearance	Artificial, irregular rust	Natural, even patina

It’s clear that Corten+ provides the safest, most durable, and most economical solution for achieving a beautiful Corten finish.

Step 3: Protecting the Surface

Once your steel has reached the desired rust color, the next step is protection. This step is crucial, especially for outdoor applications like planters, fire pits, façades, and garden sculptures.

Why Protection Is Necessary

Even though Corten steel is weather-resistant, the rust layer can still release rust run-offs when exposed to rain or humidity. These brownish-orange drips can stain nearby surfaces such as stone, concrete, marble, tile, or wood. In addition, if someone brushes against a Corten surface, the rust powder can transfer onto clothes, leaving stubborn stains.

To avoid these issues, it’s important to seal the surface with a suitable Corten sealer (also known as a varnish or protective coating).

The Benefits of the Corten+ Sealer

The Corten+ Sealer was specifically developed for Corten steel. It forms an invisible, breathable, and waterproof layer that protects both the metal and its environment.

Main Benefits:

Prevents rust run-offs and stains on surrounding materials.
Protects clothing and skin from contact stains.
Locks in your preferred patina color.
Stops further darkening of the rust over time.
Easy to apply — spray or brush-on formula.
Durable and long-lasting.

How the Color of Corten Steel Evolves Over Time

After treatment, Corten steel’s color naturally evolves over the months. Initially, it appears bright orange, then gradually darkens to deep brown-orange as the patina matures. This process can take up to one year in natural weather conditions.

However, some users prefer to freeze the color at a specific shade — for example, keeping the light orange tone rather than allowing it to darken further. The Corten+ Sealer lets you do exactly that: once applied, it stabilizes the color and stops the oxidation process at your chosen stage.

How to Apply the Corten+ Sealer

Wait until the steel has developed the desired rust tone.
Make sure the surface is completely dry.
Apply the sealer evenly using a sprayer, roller, or soft cloth.
Let it dry according to the manufacturer’s instructions.

The surface will become water-repellent while keeping its natural matte appearance. Unlike conventional varnishes, the Corten+ Sealer does not create a shiny or artificial look — it preserves the raw beauty of the metal.

Practical Applications: When and Where to Treat and Protect Corten Steel

Corten steel can be used in many contexts, but the treatment process can vary depending on the environment and the object.

1. Garden and Landscaping

Corten steel planters, borders, and fire pits are popular choices for modern outdoor designs. However, these items are directly exposed to rain and soil moisture, which can accelerate staining. Applying the Corten+ Rust Accelerator followed by the Corten+ Sealer ensures controlled oxidation and long-lasting protection against rust drips on terraces or paving stones.

2. Architecture and Facades

Architectural façades made of Corten steel must maintain a uniform appearance over large surfaces. In this case, professional surface preparation (sandblasting or descaling) is crucial to avoid uneven patina. After oxidation, the Corten+ Sealer helps preserve the chosen tone and prevents uncontrolled aging.

3. Artistic and Decorative Pieces

Artists often use Corten steel for sculptures or wall panels. Because these works are sometimes installed indoors, they require special attention: rust particles can easily stain walls and floors. The Corten+ Sealer prevents this, keeping the artwork clean and safe to display in any setting.

4. Furniture and Interior Design

Corten steel tables, lamps, and decorative elements are increasingly popular indoors. Since these pieces won’t naturally rust, you can use the Corten+ Rust Accelerator to create a uniform patina, then seal it with the Corten+ Sealer to prevent rust transfer and maintain a clean finish.

Step-by-Step Summary

Step	Purpose	Product to Use	Notes
1. Preparation	Clean and ready the surface	Corten+ Descaler (hot-rolled) or Corten+ Degreaser (cold-rolled)	Essential for even rusting
2. Oxidation	Accelerate natural rusting safely	Corten+ Rust Accelerator (acid-free)	Produces uniform, authentic patina
3. Protection	Seal and stabilize the finish	Corten+ Sealer	Prevents stains and locks color

Why Choose Corten+ for Your Corten Steel Treatment

Corten+ is more than a product brand — it’s a complete treatment system for Corten steel. Each product is designed to complement the others, ensuring a professional, safe, and long-lasting result.

What Makes Corten+ Unique

Acid-free technology: 100% safe for steel and users.
Professional-grade performance: Used by architects, landscapers, and artisans worldwide.
Complete solution: From cleaning to oxidation and protection.
Fast international shipping: Thanks to a global logistics network.
Cost savings: Fewer products, faster application, and no neutralization required.

When you choose Corten+, you invest in quality, safety, and durability. Our products are designed specifically for the unique needs of Corten steel — unlike generic acids or degreasers that can do more harm than good.

Final Tips for Corten Steel Care

Never use acids on Corten steel — they will permanently damage it.
Always clean the surface thoroughly before oxidation.
Apply products in dry weather and avoid high humidity or direct sunlight.
Wear gloves to prevent fingerprints from affecting oxidation patterns.
Allow enough drying time between steps for best results.
Seal your steel if it’s exposed to rain, clothing contact, or nearby surfaces that might stain.

By following these steps and using Corten+ products, you can ensure that your Corten steel projects — whether decorative, architectural, or functional — will retain their beauty and integrity for years to come.

Where to Buy Corten+ Products

All Corten+ products — the Descaler, Degreaser, Rust Accelerator, and Sealer — are available on our official website. We ship quickly and safely worldwide, ensuring that you receive your products wherever your project is located.

Explore our full range and discover how Corten+ can help you treat, protect, and perfect your Corten steel with confidence.