Monday, August 6, 2012

Rusting Perfectly Good Metal

Back in the day I remember seeing old buildings with metal roofs that were rusting and thinking how cool they looked. There was something about them that reflected an aura of gentle aging, of the graceful passing of time. Today, with a little help from chemical science, we can speed things along and have that 'aged in time' look in an afternoon. Corten was the first 'rusting' metal alloy that I remember and was quickly accepted as the material of choice for guard rails on highways throughout the nation. The logic of the Corten metal is to combine dissimilar metals into an alloy that produces a kind of self sealing finish, a rust that stops rusting.  A stabilized rust. It took a few years but that same technology has moved into the construction mainstream. The relatively high cost of this type of metal has helped to popularize cold rolled steel as a viable 'rusty' alternative. Allowed to weather in nature (or 'rushed' with the use of added corrosive materials) it produces a more organic patina than the very uniform look of Corten type alloys. The natural look of rusted cold rolled steel and it's greater cost effectiveness made our choice easy. Because of our climate (dry) and the wall wainscot installation (dry) we needed to speed Mother Nature along by pre-rusting the raw metal before installing it on the building.

Here comes the 'smarter than' part. You would think that just spreading on some muratic acid or vinegar would produce the desired effect. Wrong. Again, we are in a hurry here, time is money and all that. The process of cold rolling steel is itself an issue. The pressure necessary to produce the product seals the metal surface from the quick action we would hope for. Add to that the small amount of oil that is used to keep the cold rolling process running smoothly and you have another layer of protection against the immediate 'ravages of time' effect we are trying to produce.


New, untreated corrugated steel

In the past I have used a biodegradable but industrial strength soap to hurry along the etching effects we look for on galvanized metal, but with this material it seemed relatively ineffective. I had heard from others that sand was a key to help abrade the surface to receive the corrosive effects of the acid.  First I sprayed the surface with diluted muratic acid, then sprinkled on some sand, and with a medium soft floor broom proceeded to rough up the metal surface. This worked fairly well but I still had to spray on a second coat of acid and do more brushing to get anywhere close to the surface patina I was looking for.  

Prepped with Acid & Sand

I next tried to use salt instead of sand and/or in conjunction with sand to speed things up. This worked fairly well but the early patina produced by this mix was not particularly attractive. Still not satisfied with the effectiveness of my attempts at instant rust, I went against my stubborn maleness and asked somebody who knows. Barry Stromberger of "The Slag Works" has been working in metal and metal patina for most of his not insignificant years. He had the answer, ferric nitrate: "Just mix with water in the correct proportions  and (after the initial roughening of the surface), spray it on and watch it go".


Perfectly Rusted Wainscot


 I love this stuff. If you have properly prepared the surface, with little effort you can  produce a gorgeous and natural looking rust patina that will range in color from a kind of yellow gold (short duration) through a very organic red, all the way to chocolate brown (just let it sit). Once you are satisfied with the rust tone, rinsing with water stops the action, or close enough. The reality of cold rolled steel is that in a wet environment you will have continued rusting. In our exterior wainscot  installation and semi arid climate this should not be a problem. The galvanized corrugated roofing we have used in the past is typically 26 gauge whereas the steel corrugated material is 22 gauge, much heavier to withstand the the reality of its use.


                         This is one time where 'instant gratification' has paid off handsomely.


17 comments:

  1. You say "Just mix with water in the correct proportions and (after the initial roughening of the surface), spray it on and watch it go".

    How about a clue to the "correct proportions"?

    ReplyDelete
  2. I would also like to know the correct proportions. This is so awesome and great news!

    ReplyDelete
    Replies
    1. I left a reply under as an additional comment, Don

      Delete
  3. I too would love to know the correct proportions. I have 50 panels sitting on the lot waiting for mother nature to do its work. Way too slow.

    ReplyDelete
    Replies
    1. I left a reply under comments, Don

      Delete
  4. Unfortunately, "the correct proportions" is a moving target. I tried to show my own frustrations with the process in a later post 'rusty metal plant stand'. Many things go into making the metal rust the way we like. I am no rust expert nor did I mean for this post to imply that.
    Issues to watch for; surface preparation of the metal. Oily, new metal is the worst. I used soap and sand with a stiff broom to 'prep' before I expected to get even rusting. If the metal surface isn't right the 'rusting' agent won't bite.
    Temperature seems to be a factor, if it's cold the process doesn't work as well.
    I used ferric nitrate but muratic acid or even vinegar works to expedite the process. Ferric nitrate and muratic acid are corrosive and potentially dangerous. Try different dilutions and wear gloves and protective eyewear.
    Trial & error, creative problem solving. Smarter Than The Wood.

    ReplyDelete
    Replies
    1. Donald
      Where are you getting your cold rolled Panels ? Im in Southern Oregon and it all seems
      to come from the southwest. Im doing a wainscot like yours, great look.
      Cheers
      Michael

      Delete
  5. Hi
    Nice post. Most of the times i never spend a most of the time on any posts. But i really like you post and i read your post. Thank you for sharing and keep posting a more post on new topics

    ReplyDelete
  6. Where can someone obtain ferric nitrate? We are trying to rust corrugated roofing to use behind a picture inside our home. We have tried everything we can find, but still no rust, as we live in high desert, so it is hard to keep the panels wet. I would really like to try ferric nitrate to see if it works! :-) Thanks!

    ReplyDelete
    Replies
    1. I think your best bet is the internet. I get mine from a friend. Good luck, Don

      Delete
  7. Thanks for sharing that information to everyone, especially to those who have roof concerns. I know that, through your expertise and experience, many roofs will be strengthened in your area.

    Iko Shingles

    ReplyDelete
  8. Did anyone treat the metal after they reached the desired rust to help protect the metal from "rusting" through? I'm currently letting mother nature have a turn at our panels but was looking to protect it once I achieved my colors.

    ReplyDelete
  9. Hi Donald - I'm hoping to replace some old brick on the lower half of my 1967 tri-level with corrugated metal. I found your article when I googled rusty corrugated metal. Could you post a comment on how to install the metal? Do I need to remove the brick (would prefer to)? Thank you for sharing your knowledge!!
    Jacquelyn

    ReplyDelete
    Replies
    1. Sorry, but I just received this question today. Normal installation requires only standard metal roofing screws. Removing the brick would make installation a lot easier but fastening into the mortar could work. You should be considering what to use as a separation between the metal and your siding material above. We typically use 1 1/2" fir or larch installed at a slight pitch to shed water. Good luck, Don

      Delete
  10. Any ideas about about " old rusted truck " look where there is color ( turquoise ) along with the rust?

    ReplyDelete
  11. Great post!I am actually getting ready to across this information,i am very happy to this commands.Also great blog here with all of the valuable information you have.Well done,its a great knowledge.
    Metal Roofing Contractors in Chennai

    ReplyDelete
  12. Nice article. it is very interesting and informative. thank you for the sharing this valuable one.
    Car Shed Roofing in Chennai
    Terrace Roofing in Chennai

    ReplyDelete