To understand how sealcoating works, it is necessary to understand the nature of the asphalt pavement itself. Because of its excellent waterproofing, flexibility, and adhesive properties to bind and hold the aggregates in the pavement, asphalt has been used extensively for paving and road construction. Prior to the advent of asphalt as a paving material, roads were constructed by spreading graded aggregates over a road bed. These roads worked well as long as the stones remained in place and stayed dry. Naturally, these roads needed constant repair. Stone would shift under the traffic and the road’s load carrying capacity was severely damaged when it rained. The stone would absorb water, swell and lose its strength. But spraying asphalt on the surface overcame this problem somewhat. Asphalt paving technology gradually evolved and today the vast majority of all roads are constructed using asphalt as the binding material for the aggregates. Due to its waterproofing properties, asphalt protects the aggregates from absorbing water, thus preserving their strength and load-carrying capacities. Today’s asphalt pavement is a mixture of stone aggregate and mineral filler combined with 4.5% to 12% (average of 6%) asphaltic binder (asphalt cement). The strength of an asphalt pavement is directly related to the pavement design from the ground up. The asphalt pavement people see is only the "roof," so to speak, of the entire pavement. This "roof" covers a bed of graded stone aggregates of varying depths according to ground conditions as well as traffic requirements. This base of aggregate is what really carries the load of the traffic. The same theory applies to off-street parking lots or drive-ways. A firm resilient surface that provides a roof over the stone base will keep the pavement bed dry. It is important to have an elastic characteristic in this pavement so that it can expand and contract and still remain intact.