Asphalt grinding is necessary when overlaying a driveway or parking lot. Asphalt cracks with changes in temperature and use. Overlaying the asphalt adds a 1.5 to 2.5 inch layer over the top of the existing asphalt. Although this adds strength, it may create raised areas that will be tripping hazards or negatively affect drainage in the area. In these cases, the underlying asphalt must be ground down or removed before the overlay is added. There are a number of tools designed for use in asphalt grinding.