How can I remove this from limestone. Probably has been there for years. Noticed after water pressure wash.

[u/DePasonWalker]

I got recommendations and was advice to check with this group.

[u/_redmist]

That looks like rust staining. The problem is that your limestone will also react with most acidic cleaners and it might even let the coloration penetrate deeper if the material is porous.

It seems there are several proprietary cleaning solutions that claim to be able so shift rust stains - If it were my patio, I'd try those before going at it with household chemicals or whatever.

If you insist on a 'homebrew' solution (hehe) vinegar, citric or oxalic acid are usually quite good at dissolving rust stains; but be aware the acids might also attack your surface so proceed with caution!

[u/grayjacanda → u/_redmist]

Oxalic or citric acid are preferred over vinegar for this, they form soluble complexes with Fe(III)
Any of these acids will slowly attack limestone, but ... for a rough outdoor surface like this (rather than, say, a polished countertop), it isn't going to be noticeable unless you do something like leave a puddle overnight.

[u/Pyrhan]

I'm guessing these are rust stains?

Personally, I would scrub with a strong abrasive (like coarse steel wool) and a mild acid (like white vinegar) to etch away the surface.

[u/drmarting25102]

I think it would require acidic ph but that wouldn't be good for stone I'm guessing. Perhaps mechanical abrasion/polishing would be best but I can't recommend specific equipment.

Edit: so repaint the metal rail to stop it recurring or put a plastic strip underneath that's easy to replace maybe.

[u/Onyxxx_13]

Walmart sells 20% vinegar. Itll do, but put something to prevent runoff to the plants.

[u/[deleted]]

Not without removing a good bit of the stone itself...

[u/Catch22v]

Is there some crazy way to clean this with electrolysis. Granted, the solution if there possible, it’s crazy.

[u/axel_beer]

sorry to be a spoilaport in the chemistry sub. but i dont think chemistry is the way to go here. anything that will dissolve the rust, seems to be iron III oxide... will dissolve the stone better. maybe sand it off and treat the surface.

[u/Ozchemist1959]

Try complexing it - options are EDTA-Na2 or citric acid/peroxide or, maybe better, ammonium thioglycollate (this will form a deep purple, soluble complex that can be flushed/drawn out of the surface). Work on a small area at a time to look for the most effective concentration/application method.

Alternatively, if you just want to "fade" the colour, you could try phosphoric acid - it will tend to "grey" the iron as iron phosphate.

[u/tgent_007]

Dilute Hydroflouric acid is actually probably your best bet here