Seal coat is a layer of sprayed-on asphalt, followed by a thin layer of aggregate, particulate material that can be composed of sand, gravel, crushed stone, slag, recycled concrete or geosynthetic substances. The resulting surface is durable, flexible and weather-resistant. A seal coat can extend the life of an existing pavement structure by sealing cracks and preventing moisture entering into the underlying layers.

Seal coat illustration

Illustration: Seal Coat

Seal coat photo

Photograph: Seal Coat

A. The asphalt is applied at a rate appropriate for anticipated traffic and other factors. The thickness of the asphalt is carefully selected to maintain proper consistency and adhesion over the expected range of temperatures.

B. The aggregate is spread over the fresh asphalt. A roller presses it into the asphalt to firmly bind it to the surface. Any remaining unbound aggregate is swept off the roadway. The aggregate size may vary based on cost, availability, desired ride quality and other factors.