Tar to rusty metal removes the rust???

Traditionally about this time of the year I take down the skylights and re-install the pipes for the woodstoves for the wintertime and before I leave the
roofing I check to see if any rust or patches for tar-cement or tar-paint is needed to the steel roof. Of all the roofing materials I seem to prefer steel roofs since they are strong and long lasting and pretty to look at.
Now I ran into something while tarring spots of the steel roof. I notice if rust appears and I put tar on that rust spot and return to that spot years later and peel away the tar that the steel metal is as if there had never been any rust at all. Perhaps I made a mistake in thinking that I had the same spot. So I need to confirm this claim before I put the claim to good use.
Unsubstantiated Claim: if you have galvanized sheet metal with some rust spots and if you coat that rusty spot with tar-cement or tar-coating and years later peel away the tar, you will find underneath shiny steel metal with no signs of any rust???
I put three question marks because I am not sure of that observation.
But if true then tar would be a means of reviving old steel rusted items.
And if the claim is true, I cannot think of the physics or chemistry as to why tar can remove all rust and leave shiny bare steel metal?
P.S. And today I did some tar patching and for the first time in my life was able to not get any on my fingers or hands or clothing or anything except the roof job. I attribute that to carefullness but also to the application of vaseline to my hands in case I did get some on that it would not stick. Also I bought a cheap 50 cent paint brush that I was going to throw away after the job. So that if one anticipates the job so as to not get any tar on them, then success is attainable.
Archimedes Plutonium, a snipped-for-privacy@hotmail.com whole entire Universe is just one big atom where dots of the electron-dot-cloud are galaxies
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I suspect that you are simply removing the oxides mechanically via adhesion to the asphaltum. Sort of like mud pack treatments to remove zits or other facial crud.

Adhesion.
Steve Turner
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Steve Turner wrote:

I suspect more is going on than just adhesion. If just adhesion then as soon as it drys to rusty steel and removed would unvail shiny steel. I have not performed that experiment.
I suspect that tar is some sort of solvent of iron oxide just as water dissolves sugar or salt. That when tar is applied to rusty steel it dissolves all the rust after a year of contact. That is what I suspect but all of this is speculation.
Archimedes Plutonium, a snipped-for-privacy@hotmail.com whole entire Universe is just one big atom where dots of the electron-dot-cloud are galaxies
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wrote:

Well, one problem with the adhesion theory is that rust does not adhere very well to itself, and adheres at least as well to the underlying metal. So rather than peel off the rust to bright metal, you would expect to find some rust in the tar, and a layer remaining on the metal.
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snipped-for-privacy@aol.com (Edward Green) wrote:

I don't think so. "Tar" (generically speaking here) is slow but very thorough at permeating porous materials, and rust is porous. Viscosity is high but surface tension is low. This also explains why you don't see the rust in the tar: the particles of rust are encapsulated. You would be able to see the rust if the tar was transparent and colorless.
It would be possible to do an experiment: take the tar which has theoreticlly peeled up the rust, dissolve it in hexanes or other light petroleum distillate, and filter. Look at what's left on the filter (if anything). Appropriate controls would be needed.
Steve Turner
Real address contains worldnet instead of spamnet
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Seems to me as if tar is the best medium or mode to design a Metal Primer Coat. In which you coat all iron bridges with the tar and paint over the tar.
Whether the tar dissolves rust itself or whether some acid in the tar matrix is the dissolvent leaves plenty of room to *design* a tar that is perfect for each metal primer coat. Some metals may need a higher dissolvent and thus a better designed tar.
The characteristic of tar in that it adheres to the surface of metals is the primary characteristic. And the secondary characteristic is the dissolving power of tar to eliminate any and all rust.
Before this observation, it was thought that tar is only a passive rust preventor. The new thing I am saying is that tar has a chemistry of not only passive rust prevention but has an active chemistry of actually dissolving rust. Whether that dissolvent is innately within the tar chemistry itself or whether it is some additive to tar.
I would hazard to guess that if a tar were designed for old automobiles as a primer coat that those old automobiles can last into the future indefinitely. And that any new car rolling off the assembly lines were given such a tar primer coating would also last indefinitely as long as the owner would occasionally peel off old tar that was coming loose and applied a new coating of tar.
But best of all, instead of steel bridges and steel statues lasting for only "centuries" as a normal lifespan, with tar primer coating I envision these steel structures lifespan to zoom up into the milleniums as a normal lifespan instead of mere centuries.
Some will complain that a paint job could never say match the beauty of a stainless-steel structure of the St. Louis arch. And that this arch will never rust. But it will rust, if I am not mistaken, for stainless steel eventually gets those pock mark rust spots. And that the stainless steel can also enjoy a huge expanded lifespan if it were given a tar primer coat. But people will complain that no paint on the surface of the tar can match the natural beauty of stainless steel. I would argue that if you found the correct "painter" could make the St. Louis arch even more beautiful than its present state.
Another great application is ship hulls. Now, I wonder if barnacles and all that other junk stuff that sticks to ship hulls, whether a teflon like paint coating would detter that stuff. And whether tar for submarines is the best coating for secrecy in detection. As well as preserving the steel.
Two Theories as to how Tar Works to dissolve Rust: (i) Tar chemistry is such that it is a dissolvent for iron-oxides (ii) some additive to tar such as sulfur makes for a slight pH acid which is the dissolvent
Archimedes Plutonium, a snipped-for-privacy@hotmail.com whole entire Universe is just one big atom where dots of the electron-dot-cloud are galaxies
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The real test would be if the previously rusted area remained rust free after the tar has been removed. Now that would be a discovery.
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Steve Turner made a good suggestion that it is probably a physical effect of transferring the loosely adhering rust from the steel onto the highly adhesive tar. However.....
Did you see any of the red rust in the black tar matrix of the peels? What was the name of the "tar" product you used? Was it molten tar? Was it tar dissolved in Turpentine/Kerosene? Was it a Tar/Lignin-sulfonate/water emulsion? The latter here could have induced a slow chem reaction and converted/sequestered the rust over time into a black iron chelate. Lignin sulfonates are commonly used in corrosion inhibitors.
But, let me know what product you used, since I'd like to try your procedure on steel vents and flanges. hanson
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You just saved the Golden Gate Bridge, among others, Plutonium!
Go, file for a patent!
(Mathew Orman may help you with that)
w.
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wrote:

ahahaha......ahahaha....... Helm, there in lovely Austria, from where and when you posted that, it was Saturday, at nine-15 in the night..... That makes it reasonably plausible that you are indeed a dog, as you advertise, & a clever one at that, since you may already have sniffed so much turpentine or related spirits, on this fine autumn evening, ....that it gave you the idea that this may be patentable...wow! Big Time! .... So, be nice to Archie and Orman and they may include you as co-inventor in the patent. BTW, go easy on the stuff or it will rust your dog brain & tar your vision.... Servus, Mensch, .....ahahahaha.......ahahanson
PS: Now, Archie, What was the name product name/label of the "tar" product you used? Was it molten tar? Was it tar dissolved in Turpentine/Kerosene? Was it a Tar/Lignin-Sulfonate/water emulsion? hanson
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Helmut Wabnig wrote:

The 104 year old "Government Bridge" or Arsenal Bridge between Davenport Iowa and Rock Island Illinois is coated with black tar... and evidently always has been. I was just across it and talked with some of the workmen putting on repairs to the tar protection- well, a week ago.
The "Black Gate Bridge" will nevertheless never be so honored as the Golden Gate Bridge.
Jim Buch
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wrote in message <snips>

Archie makes reference to *galvanized* steel. It seems reasonable that sealing a rusty area for a while will allow the rust to be re-reduced by the Zn in surrounding areas. Any rust not in good electrical/mechanical contact with the Fe substrate gets yanked off by the tar when it is removed. Seems reasonable.
A more general application would be the protection of steel by the sacfificial oxidation of Zn in marine vessels. As you know, rapid progress in gunpowder and cannon are making current warships obsolete. I expect to see more "Ironclads" being built, and even full steel hulled ships! (Even though people say a steel ship can't float). Corrosion in metal ships will be a factor of much concern and worry to the Navy. I am sure any device or invention to counter it will be of much value and great utility to our navy.
Yours Allways, Tony.
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It is not that simple. The rust will not be re-reduced. That is only a hope. Fe once oxidized on the surface will remain Fe2O3, Fe3O4, FeO... rust. The purpose of the Zinc coating (galvanized, e-plated ,impact plated or in primers) is the same as you mentioned below: sacrificial. But once there is a naked spot, a thru-abrasion of the Zn layer which just slightly bigger than a pinhole, thru' the galvanized (Zn) surface, letting the naked Fe be exposed to H2O/O2 then the rusting sets in invariably. The sacrificial anode / cathode effect does not reach very far. In a perfect world Archie's Steel roof would main rust free as long as there is a single spot of sacrificial Zn left. But it unfortunately doesn't work that way because Uncle Murphy lives at the interface where everything that can go wrong ...will go wrong. In time the Fe corrosion even creeps on under the edges of the protective Zinc layer. Corrosion is an extremely complex surface(mono)layer phenomena and its theory is still by n' large a story where most practical advances in the art are experimental/empirical in nature.
However, the purpose of my posting on this is not pontification, for a change, but it is my hope to hear Archie sing and tell me the brand name of the tar product he used. Or is he the only one around who is in love with steel roofs? ahahaha.......ahahahahanson

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This is not new, tar was used as a means of preventing corrosion developing on many ferrous surfaces that weren't exposed to heat or direct sunlight. I used to see tarred machinery that was in long term storage before removable corrosion preventatives ( usually based on a water displacing fluid ( such as kerosine ) combined with a lubricant base grade and acidless tallow oil or lanolin ) were more economic. Some factories had hot baths ( steam ) to remove tar protection on equipment in storage.
Removing tar will also remove loosely attached paint and corrosion products, but it was known that tar also could keep steel bright. The problem was that all traces of the tar had to be completely removed before the metal could be treated with a permanent protective coating ( paint, electroplated metals, vitreous enamel etc.). The hassle of removing the tar wasn't worth the effort, and phosphating processes provided both better adhesion of paints and improved corrosion protection, and used hot alkaline cleaners to remove the temporary corrosion prevention coatings.
I suppose there were several advantages of tar ( flexibility, water exclusion, mops up oxygen, neutral to alkaline pH, low cost ) that allowed it to be used right up to the 1980s in applications from chain hoists and freezer chests. Another disadvantage was the physical fragility of the coating and the mess it made when handled, so tarred papers were sometimes used instead.

One of the common features of tars is that they slowly react with oxygen and will also bind some metal ions. Thick layers are reasonable impermeable to air and water, but eventually become brittle and crack, and corrosion then rockets along the tar/substrate interface, quickly causing extensive superficial corrosion.
Under certain conditions ( usually with light and heat ), tars will oxidise and crack quickly, and so they tend to leave bright steel behind when removed after being against the substrate for years. The problem is that the bright steel will quickly rust again, as the only protection the tar offered was by the exclusion of water and oxygen and binding of metal ions.
Many of the uses of tars as corrosion preventatives were constrained by the fact that if it cracked or separated from the surface it was intended to prevent, extensive superficial corrosion occuring. Sometimes the corrosion would be worse than if the metal had been left untreated ( usually pitting ) - requiring additional treatment.
If you are really interested, I suspect that a search of the metal treatment section of a library would identify sources of information on the use of tar.
Bruce Hamilton
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I used a product from http://www.rustbullet.com/ , it worked really well.-Jitney
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I used a product from http://www.rustbullet.com/ , it worked really well.-Jitney
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On 5 Oct 2003 09:16:38 -0700, snipped-for-privacy@yahoo.com (jitney) Gave us:
snip
Did you have to double post it, retard boy?
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On Sun, 05 Oct 2003 12:48:23 +1300, Bruce Hamilton

Have a look at the following:
"VOLATILE CORROSION INHIBITOR PAPER" (VCI-Paper)
Similar rust protection papers.....used for covering blanc metal parts.... Firma BRANGS + HEINRICH "Branorost-Papier"
etc etc
w.
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