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4.7 Selecting a Prime

The application of a prime and secondary treatment is the preferred option for sealing a basecourse, presenting lower risk and longer potential life span than the direct application of an initial seal.

It is typical practice to prime all newly constructed granular and stabilised/modified pavements prepared for sprayed seal or asphalt surfacings. For asphalt pavements, although desirable, a prime is not always necessary where the total thickness of asphalt is in excess of 100 mm.

It is not always possible (due to traffic management constraints) to divert traffic around the area of pavement under construction while the prime cures. In such instances an initial seal may be used as the initial treatment instead of a prime. Where an initial seal is being considered in place of a prime and secondary treatment, the risks and consequences of a failure should be taken into account particularly on roads with high volumes of traffic.

Concrete pavements and timber surfaces such as bridge decks should also be primed to assist and provide an adequate bond between the pavement surface and sprayed seal or asphalt treatment. This applies in particular to conditions where a strain alleviating membrane interlayer (SAMI) is to be applied over a concrete or stabilised surfacing prior to placing an asphalt overlay.

Priming is most effective during warm and dry conditions. Care should be exercised when undertaking priming during cooler and damp conditions. Low temperatures may extend curing time while damp conditions can prevent penetration of the primer into the base and increase potential for run‑off of the uncured primer. Primer washed off the pavement during this curing stage can cause pollution of waterways and environmental hazards (EPA Victoria 2002).