After aggregate is placed on the asphalt, rollers orient the aggregate in its flattest dimension and seat it firmly into the asphalt binder.

A pneumatic roller is recommended for all seal coat and surface treatment work. A steel-wheeled roller is not recommended because the flat, steel drum will tend to crush the aggregate, especially on the high spots. This is particularly true when lightweight aggregate is used. In addition, if the old pavement is rutted, a steel-wheeled roller will tend to bridge over the ruts failing to seat the aggregate firmly in the low spots of the wheel paths.