Corten® Frequently Asked Questions

No, Corten® Roofing and Siding products are sold as is due to its natural rusting/weathering quality. 

*Please Note: A606-4/Corten/Bare Steel should not be used on any roof under a 3:12 pitch due to standing water on a weathering steel product.

Corten® Disclaimer

COR-TEN® is a trademarked name owned by U.S. Steel.

COR-TEN® steel is becoming more popular by roll formed product end-users. Its unique look and naturally oxidizing finish make it especially desirable for many architectural projects. Weathering steel, best-known under the trademark COR-TEN® steel, is a group of steel alloys which were developed to obviate the need for painting, and form a stable rust-like appearance if exposed to the weather for several years. Weathering steel has increased resistance to atmospheric corrosion when compared to other steels. COR-TEN® resists the corrosive effects of rain, snow, ice, fog, and other meteorological conditions by forming a coating of dark brown oxidation over the metal, which inhibits deeper penetration and negates the need for painting and costly rust-prevention maintenance over the years. In simple terms the steel is allowed to rust and that rust forms a protective coating that slows the rate of future corrosion.

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Bare Cold rolled steel is used as a less expensive option to A606 Type 4 ( Commonly referred to as Corten®).
Bare Cold Rolled is widely manufactured for a variety of different purposes including metal roofing and costs less.
Both of these panels are completely different. However, they look similar in appearance.
After installation and exposure to normal weather the surface of the panel develops a gorgeous rustic finish and texture. Cor-ten® contains copper, chromium, manganese, and nickel which makes this material more expensive. Cor-ten® resists the corrosive effects of rain, snow, ice, fog, and other meteorological conditions by forming a coating of dark brown oxidation over the metal, which inhibits deeper penetration and negates the need for painting and costly rust-prevention maintenance over the years. Corten® will last longer and would be more desirable in harsh climates.

This panel will continue to rust.

The original Cor-Ten received the standard designation A 242 ("Cor-Ten A") from the ASTM International standards group. Newer ASTM grades are A 588 ("Cor-Ten B") and A 606 for thin sheet. All alloys are in common production and use.

It is also recommended that you read the recommendations and cautions which can be accessed by clicking on a profile from the home page.

Both A588 and A606-4 are weathering steel specifications and have similar chemical compositions that meet the ASTM G101 of 6.0 or higher on the atmospheric corrosion-resistance index. The difference in our products is:

A588 is available in steel plate and starts at 3/16” thickness and increases up to 5” thickness. A588 is a high strength low alloy plate used for structural applications such as buildings and bridges.

A606-4 is used for thin sheets and has thicknesses up to 3/16”. We stock A606-4 in flat sheets, coil, and panels.

A606-4 and A588 steel arrives UNRUSTED and will rust with naturally exposure to the weather.

There is no definitive answer to this question. It depends on the environment and the way in which it was installed. Many projects using bare cold rolled and corten products were installed in excess of forty years ago and there are no problems. It is likely that the panel will last at least two to three times as long as wood shingles. Corten will have a longer life-span than bare cold rolled steel. One of the most common problems is using a light gauge steel in a 24GA to 29GA range. Using a heavier gauge steel is the most important thing you can do to make your roof last. There is no warranty for either bare cold rolled or Corten, but there are a number of things that you can do to increase life span of the product.

Nothing. This material will rust on its own if left exposed to the weather. Getting the material wet will increase the speed in which it rust.

Use a heavy gauge steel in a 20GA or 22GA.
Keep the roof free of debris and falling objects.
Have a minimum slope of 3 in 12.
Prevent moisture and debris entrapment. It is not a rustproof material. If water is allowed to accumulate in pockets, those areas will experience higher corrosion rates, so provision for drainage must be made.

Weathering steel is sensitive to climates with exposure to salt laden air. It is possible in these types of climates that the protective patina may not stabilize, but instead continue to corrode.

In general do NOT use dissimilar metals with Corten.

Galvanized, Galvalume®, and zinc should NOT come into contact with Corten.

Stainless steel is compatible with Corten.

DO NOT USE RUSTED ROOFING IN THESE CLIMATES:
Climates with exposure to salt.
Climates in which the material will be subject to excessive moisture.

Corten steel requires alternating wet and dry cycles to form a properly adhered protective layer. Areas that have salt laden air, high rainfall, humidity, or persistent fog are typically not the proper environment for Corten and even less so for Bare Steel.

A606-4 (aka Corten®)
Corten never completely stops rusting. The weathering process occurs after the panel is installed. It eventually decreases and from that point on the finish acts as a protective coating for the base metal.
This protective coating essentially stops the corrosion. Laboratory analysis of the rust film have shown that the alloying elements in the steel, particularly copper, chromium, and nickel produced insoluble compounds that clogged the pores at the rust/steel interface, thereby ending the regeneration.

Yes, rust runoff will likely stain the surrounding areas.

Both, coil and flat sheets, can be used to roll form into panels. Since proper equipment is required to load/unload coils, for individuals looking to roll form panels in the field using a portable roll former or mobile roll forming machine, we recommend ordering flat sheets - since flat sheets can be fed into the machine manually. Always make sure to follow proper safety and lifting protocols when manually handling material.

Flat sheets (also referred to as flat stock) are construction materials usually purchased for design and build projects. Unlike a common pre-formed metal panel, there are no specific installation instructions. Installation of flat sheets will vary depending on your specific need. We recommend consulting with the designer or engineer of your project to determine the best installation method.

A metal’s gauge refers to its thickness, which greatly affects its resistance. Since flat sheets can be used in a variety of applications and are considered a design and build product, we recommend consulting with the designer or engineer of your project to determine the gauge required.

You can weld weathering steel using the same flux combinations so that the tensile strength of the deposited weld metal (welding rod or wire) is consistent with the tensile strength of the base metal (weathering steel). Typical tensile strength of based metal (weathering steel) is 68-78 KSI. We would advise only welding A606-4 or A588 together. Welding to other metals can lead to a dissimilar metal reaction with A606-4 or A588.

If you choose to clear coat the material, do it after the A606-4 has a good rust/patina set into the steel. If you do it prior to a good rust/patina, then it is very likely your clear coat will take off the rust.

If you add a clear coat to the A606-4 material it will likely change the surface color due to the additives in your clear coat.

We do not have a specific recommendation on clear coatings. We recommend you check with your local paint supplier and get theirrecommendation as they are the coating experts.

Screws are furnished in a Stainless Steel/Painted Koko Brown

Metal roofs in a galvanized, Galvalume®, or painted finish are normally 24GA to 29GA.
However, with Bare Cold Rolled or Corten products never use a gauge lighter than 22 GA.
The thicker gauge makes it more difficult for the material to rust through.

It is recommended to use a high temperature underlayment. We do not sell underlayment. Contact an expert in underlayment for further details.

Yes, trim and flashing is available in a 22 Gauge in either bare cold rolled or A606 type 4 ( commonly referred to as CorTen ). Also 48" X 120" flat stock is available.
There are standard details and sketches on this page. If what you need is not listed just draw a sketch and E-mail or fax it and it probably can be made.

7/8" Corrugated
The width of the panel is 37". On a roof there is 32" of coverage and on a wall there is 34 2/3" of coverage. Square footage is based upon 36".

1/2" Corrugated
The width of the panel is 26". There is 24" of coverage. Square footage is based upon 24".

R Panel & Western Rib
The coverage is 36". Square footage is based upon 36"

There are no warranties for products made from Bare Cold Rolled or A606 Steel.
In addition upon placement of order it is required that you initial a brief statement that refers to " No Warranty "
Click for a copy of the document that will need to be initialed.