What is the correct temperature range for heating bitumen mastic?

The mastic should be heated to between 180°C and 200°C, and must never exceed 200°C.

What is the minimum roof slope required before laying mastic?

A minimum slope of 1 in 100 is recommended for flat roofs to ensure proper drainage.

How should joints between successive work bays be handled?

Joints must be overlapped by at least 75 mm and carefully merged using hot mastic to ensure a watertight seal.

Which IS code governs the material specification for the bitumen mastic itself?

The material should conform to IS 3037 (Specification for bitumen mastic for waterproofing of roofs).

IS 4365

: 1967

Code of practice for the application of bitumen mastic for waterproofing of roofs

CurrentSpecializedCode of PracticeArchitectural · Waterproofing and Damp-Proofing

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This code specifies the procedures for preparing surfaces and applying bitumen mastic for waterproofing roofs. It details heating limits, laying techniques, and the treatment of construction joints to ensure a durable and watertight roofing layer.

Code of practice for the application of bitumen mastic for waterproofing of roofs

Quick Reference Values

Heating temperature of bitumen mastic180°C to 200°C

Minimum slope of roof base for drainage1 in 100

Minimum overlap for construction joints75 mm

Typical application thickness10 mm to 20 mm (often in two layers)

Practical Notes

Ensure the concrete base is completely cured and bone-dry before applying primer and mastic to prevent trapped moisture from causing blisters.

Continuous stirring of mastic in the cooker is required to prevent localized overheating; never exceed 200°C as the bitumen will coke and degrade.

If applying mastic in multiple layers, ensure that construction joints are staggered to prevent continuous weak planes for water ingress.