Rust stains are readily removed by application of dilute phosphoric acid. Phosphoric acid won't burn the concrete as muriatic can do. A phosphoric acid based product called CRC is readily avilable at hardware stores. It can also be used to clean A/C coils and screen room enclosures made of aluminum.
If the phosphoric doesn't work on the rust- use the muriatic- just dilute it a little- pour it on- work it with a stiff broon and hose it off. You can reapply if necessary. Coca Cola won't remove rust from porous concrete IMHO.
Cindy go to this website: MyCleaningProducts.com they carry a product called Rusterizer for $15.97 and it is completely organic. This stuff really works...Good luck!
what about good old forgotten about naval jelly? last time I asked where it was at the hardware store, the kid said it would be with lotions or baby products...say what!
Bar Keepers Friend comes in a can like comet,will take rust off of any thing. wet concrete and sprinkle on and make paste and leave on for hour or so and rinse off
I 2nd Berta's suggestion to remove rust stain from anything -- porous or non-porous surface. Rust doesn't stand a chance against Wink. Erased deep rust stain from carpet almost as easily as it worked on porcelain.
@ Sandy, the product is ZEP Sweeping Compound put in on and leave as long as possible. We had a contractor's car leave big oil spots in our drive way and then there were some old ones and it came right up. There is a wheel cleaner by Casterol(can purchase at auto parts store) that will loosen the oil if it still hangs around. Good luck.
CP