 on the mossy, greenish areas, and you let it sit. And it takes a while, but it will kill that moss. It will kill mildew. It will kill lichen, all those green growths that look really bad. It will kill them, and then the rain will, like, wash that away. But it's not the kind of thing where you just do it once, and it instantly gets brighter like you might. Oh, no, it's upkeep.