Ada County Highway District

Chip Seal The Process

Why is it Done?

As part of the maintenance program, crews chip seal street surfaces (including new streets) to protect from water and weather damage and to keep them in good condition. A chip seal application to a road or street has many positive benefits:

  • Maintains the existing pavement in its present condition by delaying further aging due to water and sun - this is equally important to new streets
  • Changes the texture of the road for skid resistance
  • Supplies minimal additional strength to the pavement
  • Provides a moisture barrier
  • Gives better resistance to studded tires
  • Corrects existing pavement problems by sealing cracks

Read more in our "Why Do We Chip Seal?" news article.

How is it Done?

  • Prep Work
    • The road surface needs to be properly cleaned of debris and any holes patched.
  • Asphalt Application
    • An asphalt distributor truck starts by shooting one lane at a time with hot liquid asphalt to assure an even application. The asphalt used is applied at a temperature between 140 and 180 degrees Fahrenheit. After cooling, this asphalt remains slightly flexible to maintain its hold on the rocks.
  • Rock Application
    • The chip spreader, follows as close behind as possible with a rock application, preferably within one minute. The asphalt must be fluid so the rock will be embedded into the asphalt. The rocks are an aggregate crushed to a special specification for size and cleanliness
  • Rolling
    • A rubber-tire roller is used to set the rock into the fresh oil. This is done in order to press the flat sides of the rock down and produce a tighter chip seal. It takes two to four passes of the roller to set the rock.
  • Second Lane
    • After the first lane has been shot, covered with rock and the rolling has begun, the equipment starts the second lane. The process is repeated.
  • Sweeping
    • Sweeping is done at the completion of the chip seal process to remove surplus rock from the surface. Sweeping is done as soon as possible after the asphalt has set up, normally within three to seven days.
  • Fog Seal
    • ACHD follows each chip seal with a fog seal which helps retain any remaining rock, control dust, and provide a clean canvas for new pavement markings. Fog sealing also adds life to a chip seal. This is a separate process that follows sweeping by up to three weeks


Read more in our "How Does ACHD Chip Seal?" news article.

Find out about the when and where in our  "When & Where Does ACHD Chip Seal?" news article.

Photograph of maintenance crew

For additional information:

ACHD Main Line: 208-387-6100
Adams Division 208-387-6325
Cloverdale Division 208-387-6350
Or contact us at: Tell Us

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