Weathering Steel FAQs

Weathering steel

Weathering Steel FAQs

Are weathering steel and cor-ten the same thing? Can weathering steel be painted? How long does it take for the patina to form? 

These are just a few of the questions about weathering steel we often receive. From its properties to best practices, learn more about weathering steel by reading the answers to these frequently asked questions. 

Are weathering steel and cor-ten the same thing? 

The terms “weathering steel” and “cor-ten” are often confused and used interchangeably because they are essentially the same thing. Weathering steel is the generic name while Cor-Ten® is the United States Steel Corporation’s trade name for atmospheric corrosion resistant steel. As Cor-Ten® became more popular, other producing mills began to develop their own atmospheric corrosion resistant steels (AKA weathering steels). ASTM created what is considered equivalent specifications to Cor-Ten® in most applications. The cor-ten equivalent ASTM specifications are ASTM A588, A242, A606-4, A847 and A709-50W.

How does weathering steel resist corrosion? 

The fundamental benefit of weathering steel is its ability to resist corrosion. When low alloy steels are exposed to moisture, air, and other elements, they have the tendency to rust. Overtime, this rust layer becomes porous and detaches from the metal surface. 

With weathering steel, the rusting process occurs in the same way, but the steel produces a stable rust layer, also known as the “patina.” This naturally-developed patina regenerates continuously when exposed to weather and produces a protective barrier that impedes further access of oxygen, moisture and pollutants. Essentially, weathering steel is allowed to rust in order to form a protective patina coating, which results in a much lower corrosion rate compared to other steels.

How long does it take for the patina to form? 

While many choose weathering steel because of its practical benefits, others select the steel for the appearance of its rusty, orange-brown patina. Architects and landscape designers are particularly fond of the texture and color weathering steel brings to structures and outdoor spaces. 

In its original state, weathering steel is silver in color like standard steel and develops the orange-brown color as the patina forms. The rate at which the patina forms depends on the environment the steel is in as well as various factors, such as humidity and proximity to bodies of water. In our experience, the patina forms quicker when the steel is exposed to more environmental cycles. Likewise, cold-rolled materials (18 GA sheets or thinner) form the patina quicker than hot-rolled materials (16 GA sheets or thicker). 

Can weathering steel be painted? 

While the corrosion resistant properties of weathering steel allow it to be used unpainted in structural and architectural applications, it CAN be painted. However, the surface requires proper cleaning, preparation and material to achieve a painted appearance. 

What type of welding rod or wire should be used to match the color of weathering steels?

For welding on corten/weathering steels, we recommend our Cor-Match™ products. Cor-Match™ is a weathering steel wire and electrode, which features excellent mechanical properties and serves as a weld metal that matches the corrosion resistance and the patina color of weathering steels. Cor-Match™ 80-CW is a composite, metal-cored electrode for FLAT AND HORIZONTAL welding of weathering steels while Cor-Match™ 810-W is a gas-shielded, flux-cored electrode for ALL POSITION welding of weathering steels. Learn more about our Cor-Match™ products here

Do you have more questions about weathering steel? Contact one of our experienced sales associates. As a trusted supplier of weathering steel, we are committed to providing customers with an exceptional level of service and making your buying experience easy.