Too much bituminous binder used during the construction of seal coats and surface treatments is one of the most common defects. Excess binder exudes upward onto the pavement surface and is the origin of the black and frequently sticky surface condition referred to as flushing, bleeding, or fattening up and which can lead to a loss of skid resistance. Figure 1-3 shows an example of a flushed seal coat surface.

Every element in the finished highway (width, alignment, profile) satisfies both engineering and aesthetic demands, and yet the surface is the most obvious part of the structure. A poorly designed and constructed seal coat begins its service life with a blemished appearance and a surface that may have flushed so badly that it will exhibit a loss of skid characteristics. Consequently, the finished surface satisfies neither the artistic nor the basic engineering requirements that the public has a right to expect. This manual will provide guidelines on determining the correct binder application quantities.

The application of insufficient binder leads to a loss of aggregate, because not enough binder has been applied to cement the aggregate particles into place. Sometimes the surface on which a seal coat or surface treatment is applied is so open or porous that a large portion of the binder soaks into it. Not enough binder remains on top to hold the aggregate, and it can be easily dislodged by traffic.

In general, the use of too little binder occurs less frequently than the application of too much.