METHODOLOGY FOR PRIME COAT

 

PRIME COAT

Scope

Work shall consist of application of single coat of low viscosity liquid bituminous material to a porous granular surface preparatory to the superimposition of bituminous treatment of mix. The primer shall be low porosity type bitumen emulsion complying with IS:8887 of suitable grade.

Preparation of Surface

Dried WMM surface, complete in all respect i.e. surface evenness, grade, lines and levels, shall be considered for priming. The surface to be primed shall be made clean and free from dust or segregated materials with power broom and/or blower. Hand brooms will also be used in location where sticky clay type material has coated the surface. Surface shall also be free from ruts, loose material or any other minor irregularities. Minor depressions potholes developed on the surface shall be patched by priming. When the completed WMM surface remains unprimed for long period indicating the presence of unbounded aggregate in certain locations or it is too much dried causing stresses in mechanical bonding or may cause freckling of prime material, the surface shall be rolled after sprinkling water to produce proper mechanical bonding.

Application of Primer

Primer shall not be applied when WMM surface is wet or during dust storm or when the weather is foggy, rainy or windy. Also when temperature in the shade is less than 10°C, prime coat shall not be applied.

Primer shall be applied with the help of self-propelled presser distributor equipped for spraying the material uniformly at the rate of 6 to 9.0 kg per 10 m2. Manual spraying of primer shall be avoided as far as possible except in unavoidable circumstances. Temperature of the primer material at the time of spraying shall be in a range of 20° C to 70° C to permit the primer to be effectively sprayed through the jets of the spray bar and to cover the WMM surface uniformly.

Curing

After application of primer coat surface shall be allowed to cure for a minimum of 24 hours or till all the volatiles have been evaporated from the surface. It shall also be ensured that the penetration of primer has taken place in to the WMM surface.

If primer at any place is not found to be fully absorbed, sand will be spread over the surface to blot the excess primer, any pools of excess primer left on  part of the surface shall be cleaned out over the adjacent surface in advance spreading sand.

No vehicle shall be allowed to ply on the primed surface except for laying next course. Prime coat shall be applied on the primed surface before laying next course.