So I cant find anything about this and never had this problem before. We live in Las Vegas, and pretty much all walls that separate backyards are made of CMU retaining walls. We recently had some snow and since then we've had some white stains on our walls. Is it lime? Tried scrubbing it, even used some CLR cleaner (dont know if that was a good idea or not, but made sence at the time) But we cant figure how to remove the stains ourselves. I know its a problem around here with the stains, but never had the problem ourselves. Any suggestions would be helpful!