What Is Prime Coat?

A prime coat in construction refers to the initial layer of bituminous emulsion or asphalt applied to a prepared base before the placement of asphalt pavement. This crucial step serves several purposes in road construction. Firstly, it enhances the bond between the underlying surface and the subsequent asphalt layers, promoting better adhesion and durability of the pavement. Additionally, a prime coat helps to seal the surface, preventing moisture intrusion and ensuring a stable foundation for the asphalt. By creating a uniform and well-bonded substrate, a prime coat contributes to the overall longevity and performance of the asphalt pavement, making it an essential component of the construction process.


(Acceptance Criteria: Ref. Section 502 of MORT&H


The work is consisting of applying a single coat primer of approved quality Produced by refinery, the primer used shall be bitumen Cationic emulsion (SS1)complying IS: 8887, the particular grade to be used for the work shall be gotapproved by the Engineer. The prime coat will be done only in good weathercondition.


For this primer distributor of capacity 4 MT’ shall be used. This distributing unit, so called as primer tanker is facilitating self-propelled pressure distributor forspraying the material uniformly at the rate of 7 to 10 Kg/10 Sq .m under normal temperature and pressures. Sometimes few small patches near junctions or narrow space where the primer tanker is not reachable, for those areas sprayingof primer shall be done manually after approval of the engineer.

Preparation of Road Surface

Make clean the top surface of wet mix macadam by engaging labors with wirebrush and all organic contents shall be blown up by using compressed air. The surface to be primed will be swept clean, free form dust and will remain dry.

Application of Primer

The primer will be sprayed uniformly over the dry surface using a self- propelledsprayer with the distribution bar. The sprayer proposed to use is having a self- heating arrangement, with spraying bar with nozzles having constant pressure system and is capable of supplying primer at 7 to 10 Kg / 10 Sq meter and attemperature 20°C to 60°C, so that distributor will spray uniformly unbroken spread of primer. Some times during summer we will come across the surface tobe primed will found, so dry or dusty in that case damp the surface with waterlightly and uniformly because the dry or dusty surface will cause freckling of primer. All these exercises prior to priming will be done as directed by the Engineer.
The primed surface will be allowed to cure for 24 hours minimum or even more as directed by Engineer, so that the primer will penetrate in to the base of wetmix macadam layer. In case the primer is not absorbed beyond 24-hours afterapplying then we will spray sand over the surface to blot the excess primer. Wewill take care that there will not be over priming or any pools of excess primerleft any part of the surface, which will be swept-out over the adjacent surfacebefore spreading sand.