Rusting Antique Cast Iron Statue

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Hello All
I refinished a cast iron sculpture that has been outdoor and rusting. It is over 100 years old. The finish that it had was a primer and paint with a faux finish to make it look like aged copper (verde patina look). This finish was done about 15 years ago and was getting pretty rusty. I was hire to redo it. The client wanted to get back to being able to see the metal and not the layered paint that was covering it. I sand blasted it and used non-acidic pewter-colour patina with subtle dark and light highlights, then clear coated it (all products were from sculpt nouveau).
Withing 2 weeks it was rusty! I am not sure what went wrong as their products are really good and it looked so beautiful when I finished with it.
I am now going to abandon the patina approach and go back to the primers and paints.
I am walnut shell-blasting it and then doing two coats of epoxy primer, then automotive paint, in the pewter colour, as a base, and the highlights and lowlights, then clear coating it with a 2 part clear.

Does anyone have thoughts on what I did wrong to begin with and/or advice on my next approach? This time I have to get it right. I have put so much time and effort into this project, I want it to work.

Any thoughts and feedback are welcome
Cheers


Rich Waugh's picture

When you sandblast or grit

When you sandblast or grit blast the surface of the iron is multiplied several times due to the billions of tiny pits created by the blasting. With that much surface area, it is going to rust within mere hours if not sealed somehow. I recommend immediately spraying it with 95% zinc cold-galvanizing paint. The brand I like best is Galvacon, but there are others as good. The important thing is to get stuff that is 90-95% zinc powder in a binder vehicle, and not some junk that calls itself "zinc-rich." The good stuff is nearly as good at preventing rust as hot-dipped galvanizing and is a terrific primer for subsequent paints.

For the top coats, if you want to use automotive paints, then you'll need to use what is called an "intercoat barrier primer" between the galvanizing and the automotive color. This will prevent the hotter solvents of the auto paint form lifting the galvanizing. Follow the instructions from the manufacturer and you should be fine. My preference is Ditzler acrylic enamel with the DXR-80 urethane additive, but the price will appall you. Suck it up and pay the fee and you won't have to deal with this again for twenty years.


johndach's picture

Rusting Antique Cast Iron Statue

Another source of some GREAT finishes is POR15.com They have catalyzed Urethane and other finishes and treatments. I have used their Urethane clear coat on sprayed metal coatings with good results. I will say that the clear coat was unbelievably difficult to remove once hardened. It evidently is used a lot in the marine industry for "bright work" and other items. Pricy but tough....

As to the "re rusting" of the piece you worked on..... From my understand, iron rust can "penetrate" the metal to a rather great depth. I am a bronze worker more that steel/iron but I have used some of the phosphoric dips to convert the iron oxide to phosphoric oxide (the coating on the black tools) to stop rusting before coating. Seemed to work well. I also do work via spraying on melted zinc or aluminum/zinc alloys for rust control. Zinc coatings so often make for problems, when using other finish coatings, as such coatings HAVE to be made to coat/hold/standup when applied over zinc. Zn is reactive and this can be a problem it overcoats are not specifically made to overcoat zinc.

John Dach
john@MLCE.net
web site: http://www.MLCE.net