I have an unfinished basement (can never be finished). Mine isn't moldy and is old. Why would the basement be moldy? Now, mine is musty smelling but I attribute that to the fact that half of it is crawl space. If you can, wash the mold off (I would wear some type of respirator) with a bleach water solution and then paint the walls with that Kilz stuff. What kind of walls do you have down there?