[TowerTalk] USTower anchor bolts rusting

[Donald Chester]

> I have found that Rustoleum paints are tough and really hold up well if
> enough is applied.  Either spray cans or spray gun applied.  For bare or
> HR steel, I start with a coat of red primer, then a coat of grey primer
> so holidays are visible, then two coats of the finish color, usually
> ...yellow for equipment. 
> I haven't tried aluminum paint in some time.  Certainly a lot cheaper
> than cold galvanizing.

If there is surface rust, Rustoleum "rusty metal" primer is designed for painting right on over the rust. Again, just make sure any thick or loose flaky layers of rust are sanded down, but don't  sand it all way to bright metal for best adhesion.  As I recall, it uses fish oil as a vehicle, which penetrates the rust and hardens just like aluminium paint does.  For bare shiny metal, use the regular primer.  With aluminium paint I have never used any kind of primer but just painted it right on the metal, whether bare or rusty.

Rusty metal primer also works well on wood, and is cheaper than good quality oil based primer.  I called Rustoleum and the technician agreed it should work OK on wood.  I got the idea from the time I accidentally dripped some onto my wooden porch floor and it dried for several days before I tried to remove it.  It had actually penetrated into the surface of the wood and was very difficult to remove and even then left what appeared to be a permanent stain, so I got the idea that it would  work a primer.  I painted an exterior wall using it, but it may have been only slightly better than regular wood primer, in the amount of time it took the top  coat to begin showing signs of failure, but it worked at least as well.

The problem with cold-galv is that it doesn't work like real galvanising.  Real hot-dipped is a layer of solid zinc, adhering in direct electrical contact to the steel, and the dissimilar metals set up a galvanic action, in which the zinc sacrifices itself in a corrosive environment to preserve the steel. With Cold-galv, the zinc particles are suspended in the non-conductive vehicle, just as in any other paint, which insulates the zinc particles from the steel, preventing galvanic action from occurring. With aluminium paint, the metal particles take the physical form of a thin flake, which protects the steel by more thoroughly isolating it from the corrosive elements, and does not depend on galvanic action.

Don k4kyv