what kind of mask needed for working around mold and mildew?

While most will say the "passive" dust mask is sufficient, many people have severe allergic reactions to mold and mildew. That said, I would personally feel fine with a 3M two strap face mask. Others would benefit most from an activated charcoal cartridge type respirator when working around organic vapors and particulates. They are more expensive and the cartridges have a limited work life but, your best guess is not as good as reading the MSDS material on the packaging to see what is most recommended.