Regular preventive maintenance (PM) is essential to achieving the design life of your hot mix asphalt (HMA) pavements. Experience has shown that a thin HMA overlay is among the most cost effective PM surface treatments available, combining high levels of service with long life and modest cost. There are many HMA mixes that can be used for a PM overlay, depending upon the conditions. In every case what is needed is a surface course of uniform thickness that can be laid and compacted to maximum density so as to provide an impervious surface over the pavement structure. For more information on HMA overlays for PM treatments see our Standard Practice for the Use of Hot Mix Asphalt Overlays in Preventive Maintenance Activities. and our technical documents on "Smoothseal"