There are three very important variables to keep in mind when heating asphalt pavement:
How Long Does it Take to Properly Soften the Asphalt?
As a general rule it should take approximately 8 minutes to properly heat the asphalt. Three variables effect the heating time: Weather Conditions (wind & temperature), Material (liquid content, aggregate, size, color, & age), Moisture (has it rained recently?)
How Deep Has the Asphalt Been Softened?
It is critical that the asphalt is softened to such a depth so that the repair will be an integral part of the existing pavement. A minimum of 1 1/2 to 2 inches of softening must be achieved.
How Hot is the Surface of the Asphalt Once the Proper Softening Depth Has Been Achieved?
THIS IS VERY IMPORTANT! Once the temperature of the asphalt has exceeded 425 degrees, the rate of oxidation (evaporation of oils) is accelerated. The application of an asphalt rejuvenator helps to offset this oxidation. At approximately 500 degrees the asphalt actually starts to burn rendering it useless and guaranteeing the failure of the repair. Simply raking off the burnt asphalt will not remedy the situation because a portion of the existing heated asphalt must be left untouched so that the restoration can be rolled into a heated existing surface.