Alright so this is my first time experimenting with this and it seems to be doing an amazing job so far. My biggest and most immediate question is- the black stuff left in place of the rust notably in the real deep pitted spots, is there any advantage to removing that stuff all the way down to clean bare metal before prepping/priming/etc? Or is it safe to leave it? I have heard completely opposite ends of opinions on this, looking for 100% fact. What's the "right" answer? Thanks in advance
The black stuff will wash away with soapy water. I'd clean it, if for no other reason than it is not "attached" to the metal.
I'm not talking about the loose coating of residue left on the surface, but the actual hard black material that the reaction turns the rust into. I've worked with chelators before (ie- evaporust, d-rust-it, etc) and they leave the metal the same way. It is supposedly an inert material that is mostly made up of the remaining carbon after the oxidized iron is removed/neutralized. It's still pretty well attached and would require wire wheeling/grinding/blasting to remove it
My experience is that the stuff washes away with soapy water, or in some cases with a pressure washer, leaving a plain grey steel finish. Give it a try, if it doesn't come off easily I'd leave it and prime/paint over it.
My experience has been the same as Mike51Merc,. I also use metal prep after de-rust sometimes, depends on the primer i'm using. De-rust, clean with soap and water, blow dry, etch, clean with soap and water, blow dry, wipe with rag and prime. Hope this helps
I cant say for sure but here is some additional info; I have used electrolysis for years to clean the rust out of motorcycle gas tanks, off firearms and off of other metal parts. Depending on what you use for an electrolyte (and what salts are in the tap water used) the hard black deposits are most likely sodium carbonate compounds. Sodium carbonate compounds are not magnetic and while they do a fair job of keeping air away from the surface, they wont stop rust re-development. The sodium carbonate compounds are not the same as the black finish left by EvapoRust, metal restore, etc; that black coating is a carbon rich layer, that does to some extent, wipe off. I have found it can be minimized by treating parts for shorter periods or using a diluted mix. I have painted directly over the sodium carbonate compounds left on metal after electrolysis and cant find an example in my stuff where the paint failed due to the compounds lifting. I do however make sure that everything gets a quick wire brush by hand before cleaning for paint/coating/anodizing. I have painted directly over EvapoRust treatment, only after washing and rinsing the item, and havent had any paint failures.
Hmm good info all thx I generally etch and then prep with solvent just to be extra safe before priming. Using epoxy primer this time around. This is my first pre- '60s build and taking it pretty seriously. Maybe too much lol. I'm on a really tight budget for this project so I built a pretty large tank and doing the electrolysis on the doors, fenders, hood, trunk, bumpers, etc. The shell will end up being mediablasted. first door out The one door I have in there is the first major part I've done it on and it seems to have done a great job aside from the black spots. I'm about to pull it out for the final time now and get to work on getting it ready for the next steps
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