Well hellsssssssssss bellsssssssssssssssss so good to know. I'm gonna try this outside on my saltillo tile. Our pool area has brick all around it and brick going to the pool house but our patio is all saltillo and it gets alge on it something terrible. I hate saltillo and wish I had never put it outside because of this very reason. We usually scrub it with acid/soap mixture and it take a lot of scrubbing. Vinegar is much cheaper if it will work. Thanks Betty........glad you got yours clean.