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

IS 4365: Scope Key Points & Specifications

Scope Overview (Clauses 3.1 to 3.3)

• Design Information (3.1):
  Designer must gather:

  • Roof height & access
  • Hoisting facilities
  • Plant/material positions
  • Roof slope & special features

• Construction Details (3.2):
  Include in drawings/specifications:

  • Roofing areas & details
  • Degree & direction of slopes
  • Thickness & number of bitumen mastic coats
  • Base description (concrete, timber, etc.)
  • Thermal insulation type/thickness
  • Unusual surfaces (metal, glazed)
  • Key form for adhesion on vertical/sloping surfaces
  • Special surface finishes (solar reflective, tiles)

• Time Schedule (3.3):
  Waterproofing contractor must be notified early for scheduling.

Important Specifications & References

• Use revised specifications for:

  • Industrial bitumen
  • Paving bitumen
  • Bitumen felts for waterproofing
  • Testing methods (penetration)

• Refer to Code of Practice for Damp Proofing & Waterproofing for design details.

Maintenance (Clause 7.1 Highlights)

• Well-laid bitumen mastic roofs need minimal maintenance.
• For removal, soften with hot bitumen mastic before careful removal.
• New joints must observe lapped joint principles with at least 75 mm width softened perimeter.

Example: Bitumen Mastic Thickness & Coats (Typical)

flowchart TD
    A[Design Stage] --> B[Gather Roof Data]
    B --> C[Prepare Drawings & Specs]
    C --> D[Include Bitumen Mastic Details]
    D --> E[Schedule Waterproofing Work]
    E --> F[Construction & Application]
    F --> G[Maintenance & Repair]

Summary: IS 4365 mandates comprehensive detailing of roofing areas, slopes, bitumen mastic thickness, base types, insulation, and special

IS 4365: Key Formulas, Tables & Specifications for Materials

1. Bitumen Mastic (Clause 2.1)

• Must conform to IS 3037-1965 (Specification for bitumen mastic for waterproofing roofs).
• Bitumen mastic thickness and number of coats depend on roof type and slope (see Clause 3.2c).

2. Bonding Materials (Clause 2.2)

• Use blown bitumen (IS 702-1961) or residual bitumen (IS 73-1961), or their mixture.
• Penetration of blown bitumen ≤ 45 (IS 1203-1958 test).
• Select bitumen based on local temperature and roof gradient.

3. Construction Details (Clause 3.2)

• Include drawings with roofing areas, slopes, thickness of bitumen mastic, base type (concrete, timber, etc.).
• Thermal insulation type and thickness specified.
• Special surfaces (metal, glazed) require particular attention.
• Provide keys on vertical/sloping surfaces for adhesion.

4. Timber Surfaces (Clause 4.6.5)

• Metal reinforcement layer nailed securely to timber surfaces with slope >10° for bitumen mastic keying.

Summary Table: Bitumen Penetration Limits

flowchart TD
    A[Roof Surface] --> B{Type of Base}
    B -->|Concrete| C[Apply Bitumen Mastic]
    B -->|Timber| D[Fix Metal Reinforcement]
    D --> C
    C --> E[Apply Bitumen Coats]
    E --> F[Apply Thermal Insulation]
    F --> G[Apply Surface Finish]

Note: Refer IS 4365 clauses and related IS codes for detailed thickness, slope, and coating specifications.

IS 4365: Necessary Information for Bitumen Mastic Roofing Design

Key Information for Designers (Clause 3.1 & 3.2)

• General Design Details:

  • Roof height from ground & access
  • Hoisting facilities on site
  • Locations for plant/material storage
  • Staging intervals if laid in stages
  • Roof slope
  • Special/unusual features

• Construction Details:

  • Roofing area & detailed drawings
  • Slope degree & direction
  • Bitumen mastic thickness & coats number
  • Base description (concrete, timber, hollow blocks, etc.)
  • Thermal insulation type & thickness
  • Unusual surfaces (metal, glazed)
  • Key form on vertical/sloping surfaces for adhesion
  • Special surface finishes (solar reflective, tiles, screed)

Maintenance (Clause 7.1)

• Well-laid roofs may not need frequent maintenance.
• For removal:
  • Soften with hot bitumen mastic, avoid hammer/chisel.
  • Use lapped joints when joining new to old mastic.
  • Remove old mastic to half thickness over ≥75 mm width.

Typical Roof Penetration Treatment (Fig. 8)

• Layers:
  • Metal collar all around
  • Neat/plastic bitumen grout
  • Metallic reinforcement all around
  • 20 mm bitumen mastic in two coats
  • Screeding bitumen felt underlay

Summary Table: Necessary Information Checklist

This ensures comprehensive design, detailing, and specification aligned with IS 436

IS 4365 Waterproofing Treatment: Key Considerations & Specifications

Key Points from Clause 3.2 (Details of Construction)

• Drawings: Show roofing areas, slopes, and details.
• Slope: Degree and direction critical for drainage.
• Bitumen Mastic: Specify thickness & number of coats.
• Base Description: Concrete, timber, hollow blocks, etc.
• Thermal Insulation: Type and thickness if used.
• Special Surfaces: Metal, glazed surfaces require attention.
• Key Forms: Vertical/sloping keys for adhesion.
• Surface Finish: Solar reflective, tiles, screedings, etc.

Clause 4.1: Primary Function

• Bitumen mastic must form a continuous waterproof layer.

Damp-proofing Treatment (Clause 4.6.4) — Typical Details:

General Recommendations:

• Ensure proper slope (minimum 1:80 to 1:100) for drainage.
• Apply bitumen mastic in multiple coats for durability.
• Use compatible base materials and prepare surfaces clean and dry.
• Coordinate waterproofing schedule with construction to avoid delays (Clause 3.3).

flowchart TD
    A[Roof Surface] --> B[Prepare Base (clean, dry)]
    B --> C[Apply Bitumen Felt Underlay]
    C --> D[Apply Bitumen Mastic (2 coats)]
    D --> E[Apply Skirting on Walls]
    E --> F[Add Surface Finish (optional)]
    F --> G[Ensure Proper Slope & Drainage]

Summary: IS 4365 emphasizes detailed design, proper surface preparation, correct thickness & coats of bitumen mastic, and integration with construction scheduling for effective waterproofing.

IS 4365 - Methods of Laying and Workmanship (Clause 5.5 & related)

Key Specifications & Workmanship Details:

• Insulation Bedding (5.5.5a):

  • Insulation boards laid over vapour barrier bonded with hot bitumen.
  • Boards laid breaking joints, immediately covered with isolating membrane and bitumen mastic.
  • Seal exposed edges by turning vapour barrier 150 mm over insulation edge, sealed with bitumen mastic.

• Junctions Between Bays (5.5.5b):

  • Hot bitumen mastic must overlap edges of existing bays for fusion.
  • Contaminated edges cleaned with hot bitumen before joining.

• Skirting & Upstands (5.5.5c):

  • First coat adhesion critical; form a splay on exposed bitumen mastic to shed water.
  • Metal flashing may cover exposed parts, but splay remains essential.

• Angles (5.5.5d & e):

  • Internal angles: solid fillets laid in two coats, last coat warmed and cleaned before filleting.
  • External angles: maintain full bitumen mastic thickness.

• Metal Keys (5.5.5f):

  • Metal lathing fixed on wooden kerbs or timber surfaces to provide mechanical key.

• Pipes Penetration (5.5.5g):

  • Bitumen fillet formed around pipes; metal reinforcement placed vertically against first bitumen layer.
  • Top layer built over reinforcement; metal collar fixed with bitumen grout.

Setting Out (Clause 5.3):

• Check gradients, slope directions, surface condition before laying.
• Bay sizes chosen for operator control during laying and rubbing.

Illustrative Table: Typical Bitumen Mastic Thicknesses

flowchart TD
    A[Surface Preparation] --> B[Set Out Bays]
    B --> C[Lay

IS 4365: Inspection & Quality Control for Bitumen Mastic Roofing

Key Inspection Points (Clause 6.1):

• General roof condition
• Surface regularity & underlay correctness
• Cleanliness of remelting plant
• Mixture temperature: 180℃ to 200℃
• Use of fine inert dust to aid mixture removal
• Repair of all 'blows' (defects)
• Uniform thickness & finish smoothness
• Removal of bitumen tailings
• Correct decorative pattern

Quality Control Specifications:

• Jointing: Use lapped joints; soften existing mastic perimeter to half thickness, at least 75 mm wide.
• Thickness: Typically 20 mm bitumen mastic in two coats (see Fig. 8 for pipe penetration detail).
• Base Preparation: Concrete, hollow blocks, timber, etc., must be clean and suitable.
• Slope: Ensure proper slope for drainage as per design.
• Temperature Control: Maintain bitumen mastic temperature strictly between 180℃ and 200℃ during application.

Typical Layering for Pipe Penetration (Fig. 8):

Summary Diagram (Mermaid.js):

graph TD
  A[Roof Slab] --> B[Screeding Bitumen Felt Underlay]
  B --> C[20 mm Bitumen Mastic (2 Coats)]
  C --> D[Metallic Reinforcement (All Round)]
  D --> E[Neat Bitumen or Plastic Grout]
  E --> F[Metal Collar (All Round)]

References:

• IS 3037: Specification for Industrial Bitumen
• IS 2: Rounding off guidelines
• British Standard CP 144: Mastic Asphalt Practices

Ensure all work follows these inspection points and specifications for durable, waterproof bitumen mastic roofing.

IS 4365 - Maintenance of Bitumen Mastic Roof Covering

Key Points from Clause 7.1 (Maintenance)

• Periodical maintenance is generally not required for a well-laid bitumen mastic roof.
• When removing or breaking through the roof during alterations:
  • Avoid hammer/chisel or blow lamp to soften.
  • Apply hot bitumen mastic around and over the area to soften it.
  • Remove softened bitumen carefully.
• For jointing new to existing bitumen mastic:
  • Use a lapped joint.
  • Soften the perimeter of existing bitumen to remove half its thickness over a width ≥ 75 mm.

Treatment Detail (Fig. 8) for Pipe Penetration:

Additional Specifications:

• Do not use the roof until the bitumen mastic has cooled to ambient temperature.
• Avoid damage from tools during maintenance.

Summary Table: Maintenance Recommendations

flowchart TD
    A[Alteration Required] --> B[Apply hot bitumen mastic around area]
    B --> C[Softened bitumen]
    C --> D[Careful removal]
    D --> E[Joint new bitumen mastic]
    E --> F[Soften perimeter (≥ 75 mm, half thickness)]
    F --> G[Lapped joint formed]

This ensures durability and watertight integrity during maintenance and repairs.