Top 8 Proven Steps for Prime Coat over Wet Mix Macadam (WMM)

1. Scope of Prime Coat

Prime Coat is applied over a prepared Wet Mix Macadam (WMM) base prior to laying Tack Coat and Dense Bituminous Macadam (DBM). It stabilizes the base and prevents absorption of binder from upper layers.

2. Reference Standards

• MoRTH Specifications – Clause 502 (5th Revision)
• IRC: SP: 84 – Manual of Specifications
• IS: 8887 – Bitumen Emulsion

3. Materials Used

Cationic bitumen emulsion SS-1 or MS-1 conforming to IS:8887, approved by the Engineer with valid test certificates.

4. Equipment Required

• Self-propelled bitumen pressure distributor
• Mechanical broom or power sweeper
• Air compressor for dust removal
• Thermometer and spray gauge

5. Surface Preparation

The WMM surface must be clean, dry, and free from loose particles. Light water sprinkling may be done if dusty, followed by adequate drying.

6. Application Procedure

1. Ensure emulsion temperature as recommended.
2. Calibrate the distributor for correct spray rate.
3. Apply Prime Coat uniformly at 0.7–1.0 kg/m².
4. Avoid pooling, streaking, or overlapping.

7. Curing & Traffic Restriction

Allow the primed surface to cure for a minimum of 24 hours. No traffic or construction equipment shall be allowed during curing.

8. Quality Control & Inspection

• Check emulsion quality (IS:8887)
• Verify spray rate using tray test
• Confirm proper penetration and uniformity

After Prime Coat curing, proceed with Tack Coat Application followed by DBM Construction.