Skate wax is needed to help any abrasive surface become more skate friendly. Add a small dab of skate wax to a painted curb and you're set for a way smoother grind. For non-painted curbs and most surfaces where you'll be sliding and grinding, you need to add more wax to really get the slide consistent. Skateboard wax adds a small coat of slidey wax that makes most surfaces skateable. It's' the opposite of surf wax, which is used on the board to help your feet grip.