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Posted by D Sherman [72.47.153.24] on Saturday, February 25, 2012 at 17:19:04 :
In Reply to: Also....If You Want The Very Best Rust Proofing... posted by Marty [50.68.51.62] on Friday, February 24, 2012 at 13:28:11 :
All the bridges used to be painted with red lead. As I understand it, the red lead actually combines chemically somehow with the iron and the oil to make a rust-resistant coating, so it's not just a pigment. It does seem to have very good adhesion. You find old painted ironwork where the top coat has disappeared and the red lead primer is slowly weathering and getting thinner, but I've never seen it peel off, which is more than I can say for any modern paint. The railroads usually top-coated their bridges with a flake aluminum paint, which is still very good for steel exposed to sunlight. The aluminum flakes reflect the sunlight and protect the resin underneath.
I've used zinc paint with good results on the rusty patches of old corrugated iron roofing and it's held up surprisingly well considering how much weather it's exposed to. It has a very rough texture that would probably be great for adhesion of a top coat, but tough to get a shiny finish over.
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