r/BuyItForLife • u/Patp2352 • 1d ago
Review Kohler Sink - Stain/Rust?
Recently put this new sink in, and noticed it has these stains/spots. Kohler insists it's not rust, and we are able to clean it off, but it keeps coming back. Thoughts?
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u/mrmacedonian 1d ago edited 1d ago
Could be garbage stainless steel, could just be stuff on the surface.
I had this happen when we moved into this house. I found a white paper from NASA about acid treating stainless steel (edit: remembered 'stainless steel passivation') to dissolve any surface contaminants and allow the stainless to reform it's chromium oxide layer.
I will find the relevant articles and update, but I'll summarize the process for a home user without availability of harsh acids.
- Choose your acid - A popular choice is to order citric acid online in powder form, careful as it's pure and needs to be properly diluted. edit: I removed recommending barkeeper's friend because I could not find the paper or article that mentioned/supported using oxalic acid for passivation.
- Wear appropriate gloves. Make a paste by dumping a bunch of the powdered acid and adding small amounts of water until it turns into a paste. edit: Various sources recommend 10% citric acid concentration, I'm certain mine was significantly higher 😬
- Cover the surface with a decent amount. Wait 15-20 minutes, then scrub the metal following any lines or brush finish.
- Rinse the surface, dry it with a microfiber or lint-free paper towel.
- Let it sit for 1-2weeks; the surface slowly reacts with oxygen in the air to form the protective chromium oxide layer.
I had a 'bar cart' type thing from Sam's with a stainless surface. My parents left some things on it when they covered it for the winter, and in the spring there was a bunch of rust. I sanded it with wet sandpaper meant for car painting/finishing, then I followed the steps above. It worked so well I did the sink prior to going on vacation, and the tiny rust spots have not returned 1yr later.
Again, could just be bad stainless but I would hope Kohler would use better materials.
edit: article covering citric acid passivation of stainless steel alloys - https://ntrs.nasa.gov/api/citations/20140002809/downloads/20140002809.pdf
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u/Patp2352 1d ago
Interesting, will need to try this!
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u/mrmacedonian 1d ago
I just updated some of the language to be more precise and added the link to the white paper showing that Citric Acid was as effective as Nitric Acid, which you wouldn't want to use at home.
I removed the recommendation for Oxalic Acid as I couldn't find the supporting article so just use Citric since NASA's and my experience has been been good.
Best of luck, just be aware any scratches can and will reveal deeper layers of the metal which could expose new iron, so it might be a once in a while task.
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u/mcawsm4565 2h ago edited 2h ago
The above is good stuff but first remove the active corrosion (rust) by chemically cleaning, then abrading with nonferrous abrasives (clean scotch bright is good), and then chemically clean again- aerospace production engineer (MRB) and this is how we repair our CRES (corrosion resistant steel, aka stainless steel). An acid etch to remove free iron ions will create a more corrosion resistant surface but should be unnecessary assuming the CRES has appropriate Chromium levels. Since the rust is localized this is a reasonable assumption, the passivated layer was probably just damaged by a scratch or an extended exposure to a highly corrosive material. Essentially the idea is to remove the damage and clean the area so the chromium can get back to doing it's job. Chromium oxide is a wonderful and durable corrosion resistant passive layer that forms almost instantly provided the area is clean and relatively uncontaminated by "free iron".
Edit: some good resources to explain further because knowledge is power: https://astropak.com/wp-content/uploads/2014/07/the_passive_layer.pdf https://astropak.com/wp-content/uploads/2015/01/Comparison-Of-Passivation-Modalities.pdf
Note these are from astropak, a company specializing in cleaning and passivating materials so these are are going to be slanted towards their processes but they good a good job explaining what's going on simply with nice graphics.
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u/Churlish_Grambungle 1d ago
Definitely looks like rust. What do you clean it with? Barkeepers friend?
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u/Patp2352 1d ago
Yep, barkeepers. It comes off easy enough, but I never had this problems with my parents old Steel Queen sinks
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u/Churlish_Grambungle 1d ago
Yeah, that’s super weird. It looks like rust, but does it leave pitting like rust?
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u/Patp2352 1d ago
Doesn't seem like it? Using barkeepers, or even just scrubbing with the song more vigorously gets it off, but it will come back sooner or later
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u/pandabearak 7h ago
Looks like rust from another source. Did you do any work near that sink? Or possibly dump something in it where it collected in that corner? Or even cleaned a steel object that left shavings/dust there?
I’ve worked on jobs where we were grinding something, and the grinding dust is basically particles of regular steel, which then rusts. So you got to be real careful about metal dust.
Good news is that it’s probably no big deal with your sink. Sinks are generally in a “brushed” finish, which means things can get stuck in the grooves of the finish. Just scrubbing it out will generally leave the stainless metal clean and free.
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u/alwaysworking247247 1d ago
The best about kohler is the life time warrant but you’re supposed to have a metal grate on the bottom of the sink. You’re not supposed to have stuff scratch the sink.
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u/3hirty6ix 1d ago
Mind specifying the sink model? That looks like one I'm looking to purchase. K-5281-NA maybe?
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u/almostclueless 1d ago
Carbon steel can scratch stainless and leave iron behind leading to surface rust like that.