Cor-Ten Steel paint methods for new & old metal

A. Hi, Lenford,
The actual situation isn't clear to me yet. If this is a failed Cor-Ten installation that you now wish to protect with powder coating, then what will need to be done will vary depending on its current condition.

If this is a new installation instead, can you say why you use are using Cor-Ten rather than conventional steel, which is both cheaper and for which suitable pretreatments already exist?

Maybe you speaking of a transparent powder coating to protect Cor-Ten without changing its rusty appearance?

Please clarify what you are up to. Thanks!

A. Hi again,
To the best of my knowledge Cor-Ten is deliberately designed to not be pretreated or coated, so no recommended pretreatment has been designed for it -- but the manufacturer still may have a recommended treatment.
If not, it's not very different from normal hot rolled steel in composition, so I would treat it as such and suggest a conventional 5 or 7-step zinc phosphate pretreatment before the powder coat. Good luck!

A. I found this on Modern Steel Construction

www.modernsteel.com/steelinterchange_details.php?id=283

Painting

The paint requirements for the COR-TEN steels do not differ from those for carbon steels. In locations where the outdoor environment is aggressive, the same quality paint systems found effective in protecting carbon steel are recommended for the COR-TEN steels. As noted earlier, environments which prevent proper oxide formation require the same surface protection against the effects of moisture as do carbon steel surfaces. Similar requirements apply where faying surfaces and bolted joints are involved, and where COR-TEN steel surfaces are likely to be in contact with other structural materials. To achieve the effectiveness of the protective coating selected, the stringent rules of surface preparation must be adhered to. While the designer must specify the paint system for the particular environment, the following are two examples of paint systems which have been found readily available and generally acceptable under most environmental conditions.

◦A one-coat system consisting of a high-quality air-drying rust-inhibitive shop-primer which is applied to a nominal dry film thickness of 1.5 to 2 mils.
◦A two-coat baked system consisting of 0.2 to 0.25 mils of a rust-inhibitive primer such as epoxy chromate followed by a top coat of synthetic-resin paint such as a polyester, acrylic or alkyd applied to a total dry film-thickness of 1.0 mils.
However, for prolonged exposure to water, the coating system should be upgraded to that of a tank lining.

More information can be found at www.ussteel.com. Alternatively, information about weathering steel can be found at/from Bethlehem Steel.

A. Hi,
While ideally things would be sandblasted and zinc phosphate coated before painting, that is surely a bit much for a high school project.

I would suggest scrubbing it with scrub brush ⇦ this on eBay or Amazon [affil links] and Spic and Span ⇦ this on eBay or Amazon [affil links] or similar detergent, then wire brushing and applying a rust converter ⇦ this on eBay or Amazon [affil links] to any areas of corrosion or heavy rust, then priming with something like Rustoleum Clean Metal Primer ⇦ this on eBay or Amazon [affil links] (which is okay for light rust), and finally finishing with something like Rustoleum Stops-Rust Enamel ⇦ this on eBay or Amazon [affil links] .

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey