What is the difference between Type 2 and Type 3 felt?

Type 2 has a jute-based hessian fabric, while Type 3 has a stronger, more durable glass fibre base (Clause 4).

What is the standard roll size for bituminous felt?

Rolls are typically 1 metre in width and 10 or 20 metres in length (Clause 7.1).

How is the pliability of the felt tested?

A strip of felt is bent 180° around a 25 mm mandrel at 10°C. It must not crack or show signs of detachment of the coating (Clause 10.7).

Which grade of felt is suitable for an exposed roof surface?

Grade 2 (mineral surfaced) felt is required for exposed applications, as the mineral granules protect the bitumen from sunlight and weathering (Clause 4.1).

IS 7191

: 2018

Bituminous felt for waterproofing and damp-proofing - Specification

CurrentFrequently UsedSpecificationMaterials Science · Roofing Materials

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This standard specifies the requirements for manufacturing, performance, and testing of bituminous felts used for waterproofing and damp-proofing. It covers various types (jute or glass fibre base) and grades (self-finished or mineral-surfaced) intended for applications like roofing, basements, and other structures.

Specifies requirements for different types of bituminous felts used for waterproofing and damp-proofing.

Quick Reference Values

Standard roll width1 m

Minimum mass of Type 3, Grade 2 felt (glass fibre, mineral surfaced)3.4 kg/m²

Minimum breaking strength (longitudinal) for Type 3 felt200 N/50 mm

Minimum breaking strength (transverse) for Type 3 felt150 N/50 mm

Maximum water absorption for Type 3 felt1.0 percent by mass

Pliability test temperature10 ± 1 °C

Heat resistance test temperature85 ± 2 °C

Practical Notes

Ensure the correct grade of felt is used: self-finished (Grade 1) for underlying layers and mineral-surfaced (Grade 2) for exposed top layers to provide UV protection.

Always check for the ISI certification mark on the product rolls to ensure compliance with the standard.

Store rolls vertically on a clean, flat surface to prevent distortion and damage before application.