I have a problem with trying to remove a cigarette ash stain from my balcony wall. A "friend" stubbed out his cigarette after smoking on my balcony and my attempt to remove the stain using a cloth and water just resulted in the stain becoming larger. Now it can be seen from a distance away and I cannot find any way to remove it. Does anyone have a suggestion? I had hoped that some heavy rain might help but months later the stain is still there.