Hi Gene

Are the pieces for inside or outside?

I have mostly used Corten(a-588 i think) for my rusting projects, but that was mostly to passify the customer. Although there are no guarantees, I have steel that has been sitting out in my yard for six years that, except for the finish, doesn't look much worse than it did when i threw it out there. I think the question is how long do you want it to last and is there a structural integrity issue to worry about. If 20 yrs and pure eye candy is the answer, then just making sure there is no place for water to pool up might be enough to use good old mild steel. Particularly in dry climates. If your next to the ocean, corten might not even be enough protection. I personally have had more worries brought up with regard to the runoff rather than the erosion of the steel.

Jake

Jake Balcom
Mettle Design
Lincoln, NE

Hi Gene,
Once I read about your rusting formula of salt+vinegar, I wanted to test it out, so I did in a piece of work the customer wanted a rusty finish on. The metal surface was cleaned and I applied the solution. First stages of rusting showed next day, and with a second application the rusty look intensified to a beautiful orange.Had to put it to dry even in the sun, because salt being hydroscopic the rust kept somehow moist. After it dried well, I wiped the surface, blew air on it and proceded to fix the finish with a clear coat of marine varnish as I had done some many other times on other jobs. Did it at noon to take advantage of lowest relative humidity, and higher temps. All was going ok,but late in the evening the surface was nearly dry to touch, and I noticed it was cool and sweaty so to speak. Next morning there were wet rusty spots all over the place where the varnish had sort of being displaced. Had to dry well again,wipe clean, and put about six more coats on during the following days. Gee, I hope now it all seems well sealed, that some microscopic amounts of moisture and salt don`t keep on rusting under and pop out through the varnish. In my experience, beautiful finish, but probably a formula for summer time when relative humidity is low. This is my guess, and input is appreciated. Have you had that problem too? Nelson.

Well, as Neil Diamond said, "rust never sleeps." When you use a salt/vinegar solution to rust steel, you are applying chemicals to the surface that attack the steel and oxidize it. Fine, but then what? The steel keeps on rusting, is what. So, what to do about it?

First, you have to stop the rusting action completely if you don' twant it to continue. This, frankly, is nearly impossible. You can neutralize acids, thereby leaving a salt. You can rinse off the salt, leaving wet rust. Then you dry the rust, but you still have a surface that is ripe and ready to continue rustin gat the drop of a hat or even high humidity. Why is it so prone to further rusting?

The rust molecule is several times bigger than an iron molecule. If you have one square foot of steel and then rust it, the surface is now more like ten square feet of moisture-gathering surface, and is nice and "toothy" to hold that moisture. Since steel has a pretty good thermal conductivity, when the air cools the steel cools almost immediately. As it does, moisture condenses onit from the air. The rust soaks up that moisture, holds it and feeds on it to make more rust. So you have to keep the surface impermeable to air if you want to keep the water out of the rust and stabilize it. This means a coating thatis absolutely impermeable to water or water vapor. About the only thing that really fits that bill is a high-quality automotive paint. Clear coats, unfortunately, just don't have the durability nor the impermeability of pigmented paints. So they fail after a relatively short time.

Remember I talked about how the rust molecule is way bigger than an iron molecule? That's the problem with applying any finish over rust - the rust continues to grow, popping the finish right off the surface or crazing it so water incursion happens. That's just physics and you can't really beat it, no matter how hard you try. Forget all the hype about special finishes that stop rust - they don't, in my experience. They may slow it down a lot, but they simply cannot stop it. Sooner or later, the rust always wins.

The only solution I know to have a rust finish that will hold up and not rust further in my marine environment is to do the following:

Prep the steel by sandblasting then spray it with a couple of coats of 95% zinc primer, followed by an intercoat primer like red oxide. When the red oxide primer is thoroughly dry, apply a couple coats of urethane-enhanced automotive acrylic enamel in a color that matches rust. When those coats are dry, apply two or three additional coats of the same paint but with a flatting agent added and dry-spray them to get that fuzzy, rusty look. Properly done, most people cannot tell this painted finish from natural rust, but it will last for years with no degradation and no rust trails on everything underneath it.

Ahhh....my old friend and enemy....RUST...

To fight the rust is to fight the natural order of things....All leads to decay....You must become one with the rust, appreciate its beauty and ignore the pitting. To fight the rust is to court madness and despair....

OK....no more wine and I'm off to bed...

Happy rusting!!

Peter

I have also used a solution of vinegar and salt to get rust, but the recipe I used also adds hydrogen peroxide. I use it on outside pieces when I first finish them so the client doesn't have to wait for the rust look. I have also used a commercial rust patina on inside pieces and clear coated them with acrylic. Several bar stools I made still look exactly the same after 2 years (this is in Arizona, so there isn't much humidity). I have made some Raven sculptures (for outside) that I gun blued and then coated with the same acrylic and they are rusting through the clear coat. I spoke to a gun smith and he suggested a clear coat made by Dura Coat that can be applied over the gun bluing. Has anyone tried that? Lin

Corten is not too difficult to get hold of - there are plenty of worldwide stockists who can sell large and small quanitities (in some cases, even offcuts). These people might be able to help you or certainly should be able to point you in the right direction..

Corten Steel Supplier