COR-TEN Steel (Corten steel) cutting

So I’ve been doing research on Corten or COR-TEN steel for exterior rust appearance projects. Has anyone cut this on a plasma table? Anything to know or watch out for?

This girls video explains it a bit.

my last job we used tons of the stuff, flat stock round bar etc…

for all intents and purposes (for us anyways), it was worked, formed, welded and cut just like plain old a36.

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As @cmalooski1 said it should cut just like regular steel, it has a small amount of copper in it but I wouldn’t think it would be enough to require additional power to cut. Technically you are supposed to use a like welding wire/rod, however for most stuff 1/4" and under you can get away with regular wire as I think the theory is the weld will mix the alloys from the base metal with the weld metal. You may end up with slight dissimilar weld colour when it starts to oxide.

The one thing not mentioned in the video is that corten will continue to rust if exposed to running water, submerged etc. It needs a chance to form the oxide layer otherwise it behaves the same as mild steel.

If you want to kinda get the look at a reduced cost, get some root killer at Home Depot, make sure to get the kind that are crystals. It’s copper sulphate. Mix with water and spray on the metal, you can use heat too, to help bring out the colours.

This was done 10 years ago out of 11 gauge mild steel with the copper sulphate.
First two pictures are from 10 years ago

This is from a few months ago, there’s basically no deterioration

I live in the north east where it’s exposed to rain and snow.

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So after 10 years, no major rust through?

No. Looks about the same as it did 10 years ago, maybe a bit more “caulky” surface but no major flaking etc.

11 gauge will last a long time not exposed to salt.

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Well, we are on the coast in North Carolina, so salt is in the air to a certain degree. I have a project to enclose the lower deck and cover the block in steel panels. Nothing is structural, just for the look.

Is this the same stuff? It says it’s " Copper Sulfate Pentahydrate"

That’s a really cool look. Great weather resistance too. Nice for some art & architectural projects.

Thanks for all the replies.

I did some price checking locally on COR-TEN vs Std A36.

11ga A36 $74.00 4’x8’ sheet

11ga COR-TEN $220.00 4’x8’ sheet

Big price difference. It is cosmetic only, so the question is long-term reliability. If i treat the A36 on the back side with a Waterproof Coating, and let the exposed side go untreated until the desired patina is achieved and seal it, what kind of life span would you predict?

This is a quick Photoshop mockup idea. Before and after.

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With either metal I think the key to having it last long is not having it in direct contact with the soil, and have your downspouts aimed away from the wall. If you have it in direct contact with the soil it will constantly wick moisture and the oxide layer will not have a chance to form so it will continue to rust. There are some large buildings that were clad in corten but wherever water collected they rusted. It’s not like stainless.

OK now I see your rendering (looks good!). This is just my opinion, but I don’t think corten will gain you much in this case. I would use regular steel, if any of it is below grade I would paint both sides up to grade, use black so it hides if exposed. Then leave the rest to rust either naturally or if you want try the copper sulphate. You might want to get cold rolled to make your life a bit easier so you don’t have to remove the mill scale. If you are just going to let it rust naturally then hot rolled with mill scale will be fine, but where you grind will stick out for a bit while the rust forms.

I did try to clear coat mine, with an automotive clear coat. I’m not sure if it was because I failed to neutralize the copper sulphate or that the clear coat I used (meant to be used over a base coat colour) wouldn’t adhere to bare metal/rust, but it all peeled off a day after I sprayed it. So I would caution you to do some experiments on some test pieces to find a system that works for whatever method you go with.

If you use 11 gauge I think it would last a lifetime. Even without clear coating. Just be mindful of any place water will collect and paint that. Like if you use a square tubing for supports, and have any running horizontal. But again, 11 gauge is ‘stupid’ thick and in a vertical application like this, should last a lifetime.

If you go with the corten I would do the same, paint both sides of anything below grade, then I would leave it to form it’s natural patina and not add any coating to it. It will end up going darker though.

@TomWS yes that should be it. Just mix with water, as with any chemical read the warnings.
Here are some pictures from applying the copper sulphate
First two, applied with no heat

my notes say “light spray no heat”

I then applied heat to the metal with a rosebud tip, then sprayed, for a deeper red/brown. I’m no expert in this, I’m not sure if the heat is needed or if time would have done it as well.

You can also use vinegar, although not as red as the copper sulphate. This youtube channel has some examples.


Good information. I was planning on applying a black epoxy to the back and ground contact areas. The areas it does touch the ground will be gravel with mulch upto the gravel. The downspouts are all pipes in the ground to a central drain on the property.

I will need to play around with the rusting effect. I may go a bit less than 11ga, but want it to hold up long term, 10-15 years.

Thanks for the video link.