I am (very slowly) renovating houses on the side to turn them into rentals - future retirement income. On my current project house, a pump type soap dispenser began to leak on the edge of the kitchen sink soon after I bought the house. I ignored the soap scum and pulled the sink for reuse after I reconfigured the kitchen. Half a year later, I was ready to reinstall the sink and I tried to clean the soap scum off and there were half a dozen rust spots (about 3/16 dia) in the stainless under soap scum. I knocked the red rust down when cleaning the sink but now I am left with black spots (that I suspect will return to red rust if they get wet). I have considered trying to buff the spots (pits?) out with a scotch bright pad on my right angle die grinder. Anyone have experiance with trying to buff rust out of stainless? How deep might I need to buff?
You will need to remove all the pitted area and then you will need to polish the ground/sanded/scotchbrighted area to at least a reasonable facsimile of the existing sink finish.
Or a quick and dirty way is to use a "stainless passivater" which is usually hydrochloric acid - the stuff I use is about 20%, which will remove the corrosion. However, my experience (mostly on boats) is that the shinier the finish the more "stainless" it is.
You can probably do this with an electric drill with some sort of spindle to hold the buffing pads if it is a one time project.
Bruce-in-Bangkok (correct email address for reply)
Since stainless steel doesn't rust the marking should only be on the surface. In that case you won't need to buff very deep. Of course the metal isn't very thick so there's still a slight chance of breaking through. There's also a chance that what you think is rust isn't and it goes all the way through. I don't know about the US but here in UK 2nd hand SS sinks are so plentiful you can't give them away. I picked up one from my local tip for =A33 ($5) recently.
The "rust" is caused by rubbing off the protective coating that forms from the non-ferrous ingredients in stainless steel, chromium or some sort of oxides it forms, for instance. What is exposed is the tips of iron particles, which are now free to rust. Also, the "stainless steel" does contain some carbon. These carbon particles can also be exposed by grinding, polishing, etc.. They are black. So, what you need to do (and this is what another poster talked about, is to eat up those protruding iron and carbon particles so they just aren't there any more. Then the "black" goes away since that carbon particle isn't there any more , and the rust can't form because that iron particle isn't there any more, either. Then, after you have applied the whatever-it-is passivating solution, I guess the chrome oxides or whatever, reform and protect the surface. So the deal is to come up with a chemical that will eat up the bad guys without killing you. No amount of polishing will solve your issue, it'll only get worse as you uncover more and more of the above mentioned bad-guys.
There's a lot more to it than that. I'm afraid I already built you a watch, and I don't even know what I'm talking about! If I got some of this wrong, please,anyone, correct me. This is just my take on the subject and going through this process several times over the last many years. Every time I think I understand, then some new problem comes along.
Personally, I use oxallic acid for this purpose. And I think the stuff I get (can't find it right now) is something like "Barkeeper's Friend Stainless Steel Cleaner" which you can get at most grocery stores. Just check the label to be sure in contains oxalic acid.
"Passivating" is both and art and a science, as I see it. Google it to see what I mean.
One last thing, for future reference: NEVER use abrasive materials on stainless steel that have already been used on "regular" steel. They WILL have some iron particles imbedded in them that will transfer to your stainless stuff.
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