[Joe K]

Electrolysis works well to "convert" rust. But it converts red-rust - which can't be painted over - to black rust which can.

I don't have the chemical formula of the various rusts in front of me.

Many who do electrolysis will follow up with some sort of mechanical removal for the black rust. Generally it remains in pits and hollars and can still be a good foundation for paint - but it will be better and possibly more dimensionally true, if the black rust is removed with a quick bead-blast, wire brush, or even scotchbrite pad.

THEN one would do best to do a phosphate treatment by its various names. Ospho was mentioned, but I've used Phosphoric Acid Kleen-Strip "Prep & etch" which used to be sold under that name but now is sold under "concrete/metal prep." All of these are similar with Phosphoric Acid as a constituent.

Curiously, the Kleen-Strip product recommends a dilute (with water) application of their product. I use about 50-50 with warm water. And then finish up after an hour or two "sit wet" with another warm soapy water wash.

A gas is generated during phosphate application to the metal. Quite suffocating I suspect this is not good for one's lungs so you maybe best do this phosphoric acid step outdoors - or at least in a well ventilated area.

I have commented previously that electrolytic rust removal does a PERFECT job of converting rust for painting. Chemical perfection that is. The problem is it also offers afterwards a perfect "landing place" for chemical atmospheric oxygen to land and re-start the rusting process. Think of all those chemical bonds of iron just waiting for an oxygen molecule to come by so it can revert it to iron mine tailings.

It is considered by some that bead or grit blasting "covers" in mechanical impact these bonding sites. Similarly, Phosphoric Acid chemically fills them, and may fill them better working on the atomic level as it does.

One of the larger pieces I have cleaned electrolytically is a Worthington Steam Pump of smaller size. It sat in the bath for a week or so and I periodically changed location of the electrodes and added chemical to the bath. As it came out of the bath, I washed everything with hot water in a tub. THEN I applied Prep & Etch. And after sitting a few hours wet, then washed again with warm soapy water.

That pump body was not a high priority - so I let it sit in my shop - for over a year before it was painted. The shop is dehumidified in the summer, but otherwise the pump was not protected until it was painted. I could not detect any rusting to red rust and little change in appearance. It's now painted.

Right now I have a Model A wheel which was electrolytically cleaned, and then Phosphoric Acid treated. It's a black to dull grey in appearance now six months later. No red rust. I should get back to that before I lose ground.


Joe K