What will work best to try to remove it would likely
depend on what the stain is. For example, if it's rust
colored, I'd try one of the CLR type rust removers.
If it's something oil based, then a detergent type
cleaner. One of the concrete cleaners could be a choice as well.

I'd be careful with those chemicals. Limestone, like marble, is a form
of calcium carbonate and acid will (slowly) dissolve it. I would suggest
to call the workers (and their boss) back and have them fix things.
Hopefully final payment has not yet been made.


I haven't done it myself but my dad used to use ground limestone to
"clean up " limestone tombstones.

He would sprinkle the lime "dust" onto the stone and then brush it off
with a hard fiber bristle brush. The powered lime seemed to wick up
some of the stands.