bitumen mastic for tanking and damp-proofing
1987 Edition

According to IS 5871, the bitumen used in mastic should contain 15% to 17% soluble bitumen by weight. The bitumen must be heated to temperatures between 170°C and 180°C before mixing. Aggregates are heated separately to 190–205°C, and mixing occurs without exceeding 205°C. The final mastic should exhibit a semi-fluid consistency at approximately 180°C, allowing it to be easily compressed into a uniform, compact layer. The aggregate gradation must include particles passing 75 microns (42–52%), between 75 and 212 microns (3–10%), between 212 and 600 microns (15–25%), and between 600 microns and 2.36 mm (7–20%), with no particles retained above 2.36 mm. This gradation ensures a dense, flexible, and impermeable mastic suitable for damp-proofing applications.

For effective preparation per IS 5871, aggregates and fillers are blended and heated to temperatures ranging from 190°C to 205°C. Separately, bitumen is heated to between 170°C and 180°C. The heated bitumen is then combined with the hot aggregates in a mechanically agitated mastic cooker, ensuring the temperature does not surpass 205°C during mixing. The cooker should discharge the entire batch within 30 minutes. At around 180°C, the mastic attains a semi-fluid state that can be easily compressed by trowels into a consistent, compact layer. This method maintains uniformity, prevents overheating, and preserves the quality and workability of the mastic.

IS 5871 recommends using fine aggregates such as natural sand, crushed limestone, or crushed hard rock, blended with mineral fillers. These materials should be properly graded and heated to 190–205°C before the addition of bitumen. The bitumen itself is heated separately between 170°C and 180°C. The combined materials are mixed mechanically, not exceeding 205°C, to produce a semi-fluid mastic suitable for forming compressible, compact, and uniform layers for waterproofing.

Yes, IS 5871 allows for bitumen mastic to be pre-produced in factory conditions, cast into blocks, and transported to project locations. These blocks should be broken down into manageable portions on-site, then reheated and remixed before application. The mastic, when heated to about 180°C, should maintain a semi-fluid consistency that is easily compressible with trowels. Sampling procedures require collecting pieces from a minimum of six randomly selected blocks to ensure quality. This approach facilitates quality control, ease of handling, and maintains the mastic’s performance during application.

Conformity to IS 5871 is determined by verifying that the bitumen mastic meets specified composition and physical property requirements, including bitumen content and gradation of fillers. The bitumen must satisfy parameters such as softening point, penetration, and ductility within defined ranges. Performance tests for water impermeability, adhesion, and durability under standardized conditions are also essential. Sampling and testing procedures, as referenced in IS 334 and IS 4911, must be followed. Products consistently passing these evaluations are deemed compliant with IS 5871 standards.