Corten Steel -- Q&A, Applications, Problems

A. Hi Gary. The runoff continues, and is a definite problem when buildings are put on concrete with no allowances for it. But whether it's enough to be a staining issue on the balance of your sign is harder to know. I suspect that if the sign is not absorbent, it's not going to be a problem.

Regards,

A. A slightly acidic, iron chloride solution should work. Take a 5-gallon plastic pail, add some rusty steel scrap, 3 gallons of tap water, some salt and a gallon of hydrochloric (muriatic) acid. Let it react until the fizzing slows down, then apply to the sculpture with a paintbrush, polypropylene bristle broom, or similar. If dripping would be a problem in the location, use a polyethylene dropcloth. Let dry overnight, then hose off.

A. Hi Maria. I think a low grade of stainless steel, perhaps a 4xx, will work. Try soda blasting [soda blaster on eBay or Amazon [affil links] it for evenness and to remove any passivation, then maybe wiping with diluted vinegar ⇦in bulk on eBay or Amazon [affil links] a few times over the course of a few days, then neutralizing with baking soda [in bulk on eBay or Amazon [affil links] and a hard rinse.

Corten / weathering steel is only "better" in that it has very little expensive ingredients in it so it's very affordable. If the project can afford stainless steel, my bet is there will be far less staining.

Regards,

A. For people whose outside Corten sculpture is staining the patio below...I would suggest that you go with the flow (of rust off the Corten)...and stain concrete to a color as close to the Corten color as you can find...and then let the Corten be...as to sealing Corten...IMHO it defeats the purpose of the material...to create an oxidized layer that, supposedly, prevents further oxidation...speaking of which...how can it really prevent that if that rusty junk keeps flowing off? Isn't it, slowly, but continually oxidizing?...if you have to seal the Corten you are better off just painting "regular" steel

A. Lanolin based oil ⇦ this on eBay or Amazon [affil links] . May have to repeat every 6 months depending on exposure to weather.

A. Hi Mario. We appended your inquiry to a thread which, if not offering a universal silver bullet, at least tells you what other people have been doing. But if you want it gray like normal steel, why use Corten? All clear coatings will deter rust, but none will permanently stop it. Good luck.

Regards,

Hi, Tim. Major national roofing companies will do this, but we can't offer brand or source suggestions ( huh? why?), sorry. Please google 'metal roofing supplier'
Regards,

She's cold steel, but she's "smokin hot", Willemine :-)

Regards,

A. To obtain a quick patina on Cor-ten you can try to use some sulfuric acid ⇦ this on eBay or Amazon [affil links] or hydrochloric acid ⇦ this on eBay or Amazon [affil links] . You will have a rusty surface within a day :-)
Careful when applying!

A. Hi Jim. You seem to be the perfect person to answer the question immediately above yours if you have the time.

1. One reason stainless steel isn't used almost everywhere is cost. It's usually about 18% chromium and up to to 12% nickel, and those metals are quite expensive compared to iron/steel. Corten is "almost" plain steel, just a bit extra of some pretty standard ingredients in steel making, totaling under 3%. So its cost is closer to plain steel than to stainless steel. The best description may be "weathering steel".
2. It's welded like steel but with proper rods, and there are warnings that the weld zone may not patina like the rest unless some special things are done.
3. Like other steels, the approximate weight is .284 pounds per cubic inch.

Good luck with the article.

Regards,

A. Hi Dave. Corten is essentially steel, with a couple of percent of alloying materials -- so whatever that means in terms of fire rating :-)

Regards,

3M Spray Adhesive
#90

on eBay or

Amazon

(affil links)

A. Hi Larry. Corten is essentially steel. There is little difference in composition. So I would suspect that soda or bead blasting is probably fine; you don't want to try to glue to rust. The right solvent for cleaning the plastic probably depends upon the type of plastic, but I think acetone ⇦ this on eBay or Amazon [affil links] Warning! highly Flammable! would work if you don't overdo it (the acrylic may be soluble in acetone). There are lots of adhesives ⇦ this on eBay or Amazon [affil links] but I don't like to say one is better since any of them should be fine.

Regards,

A. Hi Lee Ann. My understanding is that Corten is quite similar to plain old mild steel, so I don't think it work hardens, and advice about machining mild steel probably applies to Corten. Yes, I think it's easily drilled and doesn't require exotic drill bits.

Regards,

A. Hi Deanne. We appended your question to a thread which may answer it for you. Please see the 'Achieving even rusting' subheading; it suggests abrasive blasting. If you were to use soda blasting or dry ice blasting, it should be safe with little or no cleanup. Good luck.

Regards,

A. The "pattern" of rusting is highly subject to environmental conditions. Blotches can come from spills of various sorts, vertical streaks from dripping water, etc. It's also generally not a totally uniform process.

If those are steel plates supporting those plaques, then what is shown in the photos is about what I'd expect after a year or two of sitting outside. You can take action if you don't like the way it looks, but if the question is just between "is this normal?" and "is something goofy happening?" I would go with "normal".

If those are stainless steel plates, you have a major problem and they should be cleaned up and passivated immediately.

A. Hi Annie. The earth is 5% iron, so the dirt already has rust in it; your plants will be fine. As an aside, to help people understand what Corten is about: although stainless steel would rust much less than plain steel, it is way more expensive, and looks very different ... so it's impractical for a lot of applications.

But people have known for a long time that the rust on plain steel is hygroscopic, fluffy, and poorly adherent, which leads to continuing rust and corrosion. So the researchers at US Steel asked themselves whether it was possible to make some fairly small adjustments to the formulation which would be quite inexpensive and which would have little effect on the properties of the steel itself, but which would improve the adhesion of the surface rust and reduce its porosity in order to substantially slow down the rusting ... Corten or "weathering steel" is the tweak that they came up with.

Regards,

Thank you very much indeed Ted.

A. Hi Donna. Your questions require engineering work and are not easily dispatched -- which is not to say that experienced tradespersons can't play it by ear to a workable answer; they do so all the time.

Although corrugated roofing panels of the thinnest gauge commercially available will be quite strong against bending, a moderate wind will exert a good force on something 17 foot long x 24 inches high. But if you put in 5 support posts, so the span is 4' 3", it will probably prove practical. The steel posts will last longer and work better if set in concrete than if driven directly into the ground.

Regards,