We recommend installing our Coin Grid-Loc Tiles over a solid, flat surface such as concrete, plywood, asphalt, or the like. If your subfloor is not perfectly flat, that is ok. If you have mild slopes in your garage, that is ok, but if there are major peaks and divots throughout your floor, you may have to level it. The tiles will not properly interlock if there is a peak where the tiles will interlock. When there is a divot, the tiles may not stay together well if they interlock over the divot. Any pressure may cause the tiles to separate.