I made the very bad decision last summer to water two of my plants out on the front porch, not thinking about the possible effects of doing so. Sure enough, when picked up the plants, I had a big rust stain on my porch. I was pretty upset about it, because I did not know what would get it out. I went to a local hardware store and asked what to use to get rid of an outdoor concrete stain, and I got about half a dozen different answers. It was not a pleasant journey, to say the least!
The first thing that was recommended to me was some type of a cleaning solution that actually stunk to high heavens. The man who sold it to me swore that it would clean any outdoor concrete stain, and now I'm starting to think he was just having a good laugh! It spread the stain around a bit, and made it less dark, but it certainly did not get rid of it, and again, the smell made it completely not worth the money that I spent. So then I was on to the next product.
I went to another store where a sales lady swore by this chemical solution that came in what looked like an old-style gasoline can, which I thought was a bad omen from the outset. She told me to wear long rubber gloves and goggles when I used it, and not to let it sit for too long, again, not good signs. I put it on the porch, and it may have just been me, but it looked like it started to smoke a little bit, and I swear that it ate away some of the concrete on that area of the porch. The outdoor concrete stain, however, was still there, and bold as ever!
I was over at my grandmother's house one day, talking about the outdoor concrete stain, and she happened to overhear me. She called me into the dining room and said she had a really simple solution to my problem, and that was using vinegar. “It'll take it right out!” I thanked her for the advice but kind raised my eyebrows to my aunt as I was leaving. She smiled, and we left the room. Well, guess what— the vinegar worked, and finally, I had my old porch back. Needless to say, my grandmother had a bouquet of flowers sent to her as well!
An outdoor concrete stain can be a hard thing to get rid of, and believe me, I have tried just about every trick in the book. I will say, however, that using vinegar did the trick for me, and that was on a rust stain. I would imagine that if using vinegar can get out rust, it will likely be able to get rid of any type of stain.