Explanatory note: interface treatment

Interface treatment is the preparation of the surface between two pavement layers (for example, between a granular base and a bituminous layer, or between an old and a new bituminous layer) to give a good bond. The surface is first swept clean and then sprayed with a prime coat on granular bases or a tack coat on bituminous or concrete surfaces. A good interface bond prevents slippage and delamination, helps the layers act together as one structure (reducing tensile strain at the bottom of the bituminous layer), and stops water entering between layers. Interface treatment is done just before laying, with the correct rate of spray (prime coat 0.6-1.0 kg/m2, tack coat 0.20-0.30 kg/m2) and sufficient curing/breaking time.