Re: Tar dissolves rust and is the best primer coat on steel

From: Joe Cummings (joseph.cummings_at_wanadoo.fr)
Date: 11/11/04 

Date: Thu, 11 Nov 2004 08:42:32 +0100

On Thu, 11 Nov 2004 01:47:35 -0600, Archimedes Plutonium
<a_plutonium@iw.net> wrote:

>A few years back I reported to the newsgroups that when I put tar
>coating on my steel roof and years later peeled away the dry hardened
>tar that the steel revealed was crisp and shiny bright with no sign of
>any rust.
>
>So last summer I went to further test this observation. I took a old
>rusty steel putty knife and immersed it into a can of roof tar and then
>set it outside on a drum so that given 6 months of hardening and then
>today I peeled the knife off the drum which allowed me to see the
>surface of the putty knife. It was mirror shiny metal of steel as if one
>polished steel. There was no evidence of any rust.
>
>So again, I believe what has happened is that tar dissolves rust on
>steel.
>
>But I need a chemist to write out the chemical reaction taking place.
>
>Is there another compound besides tar that dissolves rust on steel to
>use as an analogy?
>
>I think the important message of this discovery would be that all primer
>coats of steel that need protection should be a first coat of tar and
>then paint over the tar. Especially important for bridges.
>
>
>Archimedes Plutonium
>www.iw.net/~a_plutonium
>whole entire Universe is just one big atom where dots
>of the electron-dot-cloud are galaxies

        What I'd expect to see on a knife that was previously rusty
was some pitting where the rust had come away from the steel.

        Are you saying that the steel was actually "polished?"

        The only precedent for this is when soda-aluminium is used to
redeposit silver.

        Have fun,

        Joe Cummings