Problems with electrolytic derusting

[Yorkshire Sam]

I recently made an electrolytic derusting bath and have used it a couple of times with pleasing results. Normally for a heavy encrustation I have left the tool overnight and it worked marvelously. Just did an old quite badly rusted Stanley plane body and finished off removing the crud with a small brass wire brush, and to my surprise it not only took off all the rust crud but most of the paint too! While the surface it left would be great if I wanted to repaint ( ie totally restore to like new ) this was not the aim. There are still some patched of the original paint adhering ( but not a lot) ...
The electrolyte I am using is a 10% solution of washing soda. Was this a case of too strong solution, too long in the bath, rust under the paint? Could anyone shed a light on what might have gone wrong here?

 

[RogerP]

I've found that rust under the paint is the usual cause of it flaking off.

The percentage of soda in the water is not critical, it's only to make the water conductive, and I've not found leaving stuff in the bath, even for several days, does any harm.

 

[Spindle]

Hi

Definitely corrosion under the paint, it doesn't have to be much at all, the electrolysis will convert it and break the bond to the surface finish. The longer you electrolyse the further under the paint the action will progress if there is corrosion to support it.

10% is a stronger solution than I use but it shouldn't make any difference to the reaction, as Roger says, the purpose of the soda is to make the water into a better electrolyte. I use a teaspoon to a gallon, any more is just a waste of soda.

Regards Mick

 

[Yorkshire Sam]

Thanks for that guys. I have only recently started doing this, so still learning. Many thanks