408 Prime Coat

Description (408.01)

Construction requirements for prime coats are included in 408. An asphalt material having low viscosity is required for a prime coat. This material is intended to penetrate a prepared granular surface prior to the placement of an asphalt concrete mixture. The purpose is to bind the granular particles together for some depth below the surface to provide additional stability.


Asphalt Material (408.02)

One of the following types of asphalt material can be used: 702.02 MC-30, MC-70, or MC-250 or 702.03 Primer 20.


Cover Aggregate (408.03)

Cover aggregate must conform to No. 9 size or gradation requirements of 703.05 or 703.06.


Weather Limitations (408.04)

Prime coat cannot be used on a wet surface.

Do not apply prime coat for asphalt concrete paving or surface treatment work when the air temperature is below 50 F or when the air temperature in the last 24 hours has been 40 F or lower.

Do not apply prime coat on stabilized or granular base courses when the air temperature is below 40 F.


Equipment (408.05)

Equipment requirements for the application of tack coat are the same as detailed in 407. These requirements include the use of tachometer, pressure gauges, and an accurate volume measuring device or a calibrated tank. A thermometer is required to monitor temperature of the tack. The spray system must by fully circulating and the spray bar must be adjustable both laterally and vertically. The Contractor must provide charts or other information that shows truck and pump speeds required to obtain the application rate.

The spreading of the cover aggregate, when required, can be accomplished by any approved method depending upon the specific job conditions. When sweeping is required, the brooms approved for use should produce a uniform surface without causing damage.


Preparation of Surface (408.06)

The surface to be primed should meet all requirements for the particular specification item (e.g., subgrade, aggregate base, stabilized subgrade, etc.). Irregularities in the subgrade, subbase, or base material in excess of specified tolerances must be repaired prior to priming. These include, but are not limited to, ruts, corrugations, and high and low areas. Mud, clumps of dirt, and other foreign material must be cleaned from the surface to be primed.


Application of Asphalt Material (408.07)

The specified application rate for the asphalt material is an estimated rate suitable for average conditions. Open textured surfaces may permit an increase, while dense surfaces may require a reduction in the estimated rate. The application rate should be such that the prime will be absorbed by the material within 24 hours.

The asphalt material must be applied uniformly over the entire width of the area to be primed. The distributor must meet the same requirements of 407.03. If excess material is applied, the Contractor should squeegee the excess from the surface. Any deficient or skipped areas must be coated.

Prime is shipped under ODOTs Asphalt Materials Certification Requirements as detailed in Supplement 1032. Weight tickets will be provided for the loads of asphalt material delivered to the project. A weigh-back ticket must be provided to accurately determine the quantity of tack used based upon weight. This weight will have to be converted to gallons based on the appropriate conversion factor for the tack. Although the distributor is required to have an accurate volume measuring device, payment must be made using the weight tickets.


Application of Cover Aggregate (408.08)

When traffic must use the primed area where the material has not penetrated completely, cover aggregate must be applied to absorb any excess material.


Method of Measurement (408.09)

Determine gallons (liters) from weight tickets or weighed partial loads (weigh-back). For weights or volumes that are questionable or unknown, a volume-measuring device is required before accepting the material. Cover aggregate is included in the bid price for the prime coat.


Documentation Requirements - 408 Prime Coat

1.      Measure and document air temperature.

2.      Document surface preparation (sweeping, cleaning) and condition of surface prior to the application of the prime coat.

3.      Document the temperature of material as delivered to the project.

4.      Document equipment used and conformance to specifications.

5.      Document the use of any cover aggregate.

6.      Document any issues with application (excess, deficiency) and actions taken to correct the issue.

7.      Calculate and document, for pay, number of gallons applied per 408.09, 408.10, and 109.01.

8.      Use form CA-FP-6 and other approved forms to document the tack application and calculations.