Slurry Seal

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Primary Resource

Before writing a specification for your slurry seal project, review the Recommended Performance Guideline for Emulsified Asphalt Slurry Seal (A105) provided by the International Slurry Surfacing Association (ISSA). This resource will help in design, testing, quality control, measurement and payment procedures for your project.


Note: It is important to keep in mind that ISSA includes recommended guidelines, not specifications. There are many important factors to consider after reviewing the A105, and your project may demand different processes and measurements from the included guidelines.

Helpful Guidelines

Use ISSA A105 and the following statements to inform decisions and provide support when writing a final specification for your slurry seal treatment:


  • Determine if any changes to the specifications as stated are required for the asphalt emulsion and aggregate per AASHTO/ASTM specifications.
  • State the storage limitations for the asphalt emulsion.
  • Determine if screening of the aggregate will be required.

Screen the material immediately prior to loading the truck mounted paver or mobile support unit. This way, there is no possibility of contamination when re-handling the material.

  • State the Type of slurry seal to be applied: Type I, Type II or Type III.
    • Type I is for low traffic areas.
    • Type II provides skid resistance, while being quieter and smoother than Type III.
    • Type III is typically used when a high skid resistance is required.
    • Note:  Many state specifications call out their own specific slurry seal aggregate types that are not exactly the same as ISSA’s.
  • Determine the application rate to be applied.
    • Note: A specific application rate must be defined based on the traffic level and expectations of the treatment.
    • General guidelines for application rate:
      • Specify at the higher end of the range for high traffic roads to provide more of a wearing surface.
      • Specify at the higher end of the range for very rough pavements, as the voids will require more material.
      • Specify at the lower end of the range for pavements with a consistent profile, or a smooth surface.
      • Specify at the lower end of the range to save money (which will lower the lifetime of the treatment).
    • Note: The roughness of the pavement being surfaced is a factor in the proper application rate (rougher surface requires more material to fill the voids).
  • Determine specific requirements for the spreader box, such as a fixed width spreader box or a variable width spreader box. Determine if a secondary strikeoff or drag will be used, or if it is up to the contractor.
  • State if the project requires a calibration in the presence of an inspector, or if a previous calibration suffice. If a previous calibration is used, state the time limitation (for example, calibration must have been performed with the same materials in the last three months).

Require a recalibration when material changes, conveyor seals, and/or emulsion pumps have been replaced.

Require the contractor to perform a calibration with the inspector on site, with the specific materials for the job. This step has a high potential for increasing the quality of the job.

  • State the specific instructions related to notification.

The agency can provide early notification by website, newspapers, signs and/or door hangers. The contractor can notify by signs and/or door hangers the day before and the day of the application.

  • Determine if a tack coat will be required.


    • Tack coat is required on extremely dry asphalt pavement surfaces, and all concrete and brick surfaces.

Speak with nearby agencies and local contractors to determine the normal practice in the area. Note that quality can be achieved on good asphalt surfaces either way, but the mix design must be prepared knowing if the pavement will receive a tack coat.

  • Determine if crack sealing will be performed before the application of slurry seal. If so, state whether it is part of the slurry seal contract, or a separate contract. If crack sealing is performed, state how much time must be allowed between the crack sealing and slurry seal operations.

Ensure crack sealing material is not excessive, as it can be picked up by the slurry seal paver tires and spreader box runners.

  • Determine if a test strip is required.
  • Determine if rolling will be required on the project.  Rolling is generally required on airports.

To increase the longevity of the slurry seal, roll parking lots, cul-de-sacs, and other pavements that will not receive regular traffic.

  • State specifically how the project will be measured for payment.
  • Determine if a pre-bid meeting will be held to discuss the specifications.

Additional Resources