If your hardwood floor is warped, stained, or squeaky, or has large gaps between the floor boards, then your floor is due for a re-finish. Make sure your hardwood floor is at least inch thick before sanding. Otherwise you could end up sanding the sub floor. If your floor is too thin then consult a flooring pro to discuss your options. Unsure whether you should go for the re-finish? Try this test: Pour a few drops of water on the floor. If the floor soaks up the water upon contact, it's a sure sign that the wood fibers are exposed and your floor needs a re-finish.