Code of practice for damp-proofing using bitumen mastic

IS 7198: Scope - Key Points & Specifications

Scope (Clause 2.1):

• Design must follow basic info as per IS 3067-1966 for efficient design and construction of bitumen mastic tanking.

General Considerations (Clause 6.1.1):

• Ensures proper design methodology and construction practices are followed.

Thickness & Laying Method (Clause 8.5):

• Construction joints:
  • Warm edges of laid mastic with hot asphalt.
  • Remove dust/dirt by cutting with a metal trowel.
  • Pour fresh mastic before surface cools.

Mixing Method (Clause 7.1):

• Follow IS 5871-1970 for mixing bitumen mastic.

Typical Structural Form (Fig. 4)

Summary Table: Thickness & Laying

flowchart TD
    A[Working Platform] --> B[Lean Base Concrete]
    B --> C[Bitumen Mastic Angle Fillet]
    C --> D[Cement Sand Protective Screed (5 cm)]

For detailed design and construction, refer to IS 3067-1966, IS 5871-1970, and IS 7198 clauses above.

IS 7198: Key Specifications & Guidelines for Damp-Proofing Design and Construction

1. Applicable Structures (Clause 1.2)

• Reinforced concrete, prestressed concrete, plain concrete (special cases)
• Dense concrete, blockwork, plastered brick or stone masonry
• Structural steel with other materials

2. Damp-Proofing for Walls and Floors Above Ground (Clause 6.1.2 & 5.2)

• DPC shall cover full thickness of walls (excluding plaster) or base of cavity walls.
• No setback for pointing; must be continuous with bitumen mastic layer in adjacent floors.
• Vertical DPC may be provided on the inner surface where necessary.
• DPC height: minimum 150 mm above ground level.

3. Surface Preparation & Laying (Clause 6.1.1.6)

• Keep surface dry during laying.
• Follow IS 3067-1966 for laying bitumen mastic.
• Maintain dewatering until bitumen layers harden and structure gains strength to resist hydrostatic pressure.

4. Typical Arrangement (Fig. 2)

flowchart TB
    A[Periphery Wall (Hollow)] --> B[Damp-proof Course (Full Thickness)]
    B --> C[Bitumen Mastic Layer in Floor]
    C --> D[Lean Base Concrete]
    D --> E[Floor Concrete]

Summary Table: DPC Specifications

This ensures effective damp-proofing integrated with structural elements.

IS 7198 — Materials Key Points

1. Bitumen Mastic:

   • Must conform to IS 5871-1970 (Specification for bitumen mastic for tanking and damp-proofing).
   • Mixing method as per Clause 7.1 follows IS 5871-1970.

2. Design Information:

   • Basic design data should comply with IS 3067-1966 (Clause 2.1).

3. Construction Joints (Clause 8.5):

   • Edges of laid mastic warmed with hot asphalt.
   • Remove dust/dirt by cutting with metal trowel.
   • Fresh mastic poured before the joint surface cools.

4. Typical Structural Form (Fig. 4):

   • 5 cm thick cement-sand protective screed
   • Bitumen mastic angle fillet
   • Lean base concrete
   • Hard working platform (rubble soling, rammed earth)

Summary Table: Bitumen Mastic Properties (from IS 5871-1970)

Construction Joint Preparation (Clause 8.5)

flowchart LR
    A[Existing Mastic Edge] --> B[Warm with Hot Asphalt]
    B --> C[Cut & Remove Dust/Dirt]
    C --> D[Pour Fresh Mastic Before Cooling]

References:

• IS 5871-1970 for bitumen mastic specs and mixing.
• IS 3067-1966 for design data.
• Use protective screed and proper base layers for durability.

IS 7198: Allowable Loads Summary

• Clause 4.1: When bitumen mastic is not properly compacted to prevent extrusion, the maximum design load should not exceed:

  [ \boxed{ 6.5 \text{ kgf/cm}^2 } ]

  at maximum atmospheric temperature.

• Proper compaction is critical to ensure mastic integrity and allow higher loads.

• For design, refer to IS 3067-1966 Clause 2.1 for basic information on load considerations.

Key Points:

Practical Advice:

• Ensure proper compaction of bitumen mastic to maximize allowable load.
• For design loads beyond 6.5 kgf/cm², verify compaction quality and consult IS 3067 for detailed design data.

flowchart TD
    A[Bitumen Mastic] --> B{Properly Compacted?}
    B -- Yes --> C[Allow Higher Loads]
    B -- No --> D[Limit Load to 6.5 kgf/cm²]
    C --> E[Design According to IS 3067]
    D --> E

This ensures safe design respecting IS 7198 provisions.

Location of Damp-Proofing Treatment (IS 7198)

Key Specifications:

• Walls and Floors Above Ground (Clause 6.1.2):

  • Damp-proofing must cover the full thickness of walls, excluding plaster.
  • For cavity walls, apply at the base of the cavity.
  • No setback for pointing is allowed.
  • Must be continuous with bitumen mastic layer in adjacent floors.
  • Provide a vertical damp-proof course on the inner wall surface if necessary (see Fig. 2).

• Height Above Ground (Clause 5.2):

  • Damp-proof course (DPC) should extend to at least 150 mm above ground level.

• Load Limitation (Clause 4.1):

  • If bitumen mastic is not properly compacted, max design load ≤ 6.5 kgf/cm² at max atmospheric temperature.

Typical Arrangement (Fig. 2)

graph TB
    A[Periphery Wall (Hollow)] --> B[Damp-proofing across full thickness]
    B --> C[Continuous with Bitumen Mastic on Floor]
    C --> D[Floor Concrete]
    D --> E[Lean Base Concrete]

Summary Table

This ensures effective moisture barrier preventing rising damp and water ingress.

IS 7198: Preparation of Surface and Site for Damp-Proofing

Key Specifications & Requirements

• Damp-proof course (DPC) height: At least 150 mm above ground level (Clause 5.2).
• Surface condition: Must be clean, dry, and free of dirt/dust before laying bitumen mastic (Clause 6.1.1.2).
• Dewatering: Continuous dewatering is essential during laying and until bitumen mastic hardens and structure gains strength (Clause 6.1.1.6).
• Continuity: DPC must be continuous across full wall thickness (excluding plaster) and continuous with adjacent floor bitumen mastic layers (Clause 6.1.2).

Preparation Steps (Summary)

• Clean surface thoroughly.
• Ensure surface dryness.
• Maintain dewatering to prevent hydrostatic pressure buildup.
• Lay damp-proofing continuously without setbacks, including vertical DPC on inner wall surfaces.

Typical Arrangement (Fig. 2)

flowchart TB
    A[Lean Base Concrete] --> B[Floor Concrete]
    B --> C[Bitumen Mastic Layer]
    C --> D[Periphery Hollow Wall]
    D --> E[Vertical DPC on Inner Surface]

Reference Standards

• IS 3067-1966: Dewatering and preparatory work.
• Specification for bitumen mastic for tanking and damp-proofing.

This ensures effective moisture barrier and structural integrity against dampness.

IS 7198 - Method of Mixing and Remelting Bitumen Mastic

1. Method of Remelting (Clause 7.2)

• Use a mechanical mixer on-site.
• Stock broken bitumen mastic blocks (per IS 5871-1970) in layers around mixer sides, then towards center.
• Gradually heat to ~200°C; do not exceed 200°C to avoid property degradation.
• Continuous agitation ensures uniform consistency.
• Total heating duration and plant type must preserve bitumen mastic properties.

2. Method of Mixing (Clause 7.1)

• Follow the procedure in IS 5871-1970 (Specification for bitumen mastic for tanking and damp-proofing).
• Clean surface thoroughly before application (Clause 6.1.1.2).

3. Protective Measures (Clause 6.1.4)

• Provide 300 mm clearance outside walls during excavation.
• Apply 50 mm thick cement-sand screed (1:4 ratio) after laying horizontal mastic and angle fillets.
• Allow mastic coats to harden before backfilling.

Summary Table: Remelting Parameters

flowchart TD
    A[Bitumen Mastic Blocks] --> B[Stock in layers in mixer]
    B --> C[Gradual heating to 200°C]
    C --> D[Continuous agitation]
    D --> E[Uniform melted bitumen mastic]

This ensures uniform mixing and maintains bitumen mastic quality per IS 7198 requirements.

IS 7198: Thickness & Method of Laying of Bitumen Mastic

Key Specifications (Clause 8)

• Number of coats: 3 (vertical, horizontal, or sloping surfaces)
• First coat: Thin, acts as adhesive & prevents blowing.
• Subsequent coats: Spread evenly and uniformly with a float.
• Vertical surfaces: First coat plastered with metal trowel; 2nd & 3rd coats with wooden float.
• Timing: Apply next coat ASAP to avoid dust/dirt accumulation affecting adhesion.

Thickness (from Clause 8.5 Table summary)

Construction Joints (Clause 8.5)

• Warm edges of laid mastic with hot asphalt.
• Cut edges with metal trowel to remove dust/dirt.
• Pour fresh mastic before joint surface cools.

Method of Remelting (Clause 7.2)

• Remelt bitumen mastic in mechanical mixer at site.
• Heat gradually to ~200℃; do not exceed 200℃.
• Continuous agitation for uniform consistency.

Summary Diagram (Laying Process)

flowchart TD
    A[Prepare Surface] --> B[Apply 1st Coat Thinly]
    B --> C{Surface Type}
    C -->|Horizontal| D[Spread with Float]
    C -->|Vertical| E[Plaster with Metal Trowel]
    D --> F[Apply 2nd & 3rd Coats with Wooden Float]
    E --> F
    F --> G[Ensure Uniform Thickness]
    G --> H[Apply Next Coat ASAP]
    H --> I[Finish with Construction Joints Treatment]

This ensures proper adhesion, uniform thickness, and durability of bitumen mastic as per IS 7198.

IS 7198: Precautions for Internal & External Tanking

External Tanking (Clause 6.1.3)

• Working space outside walls: ≥ 0.6 m
• Base: Structurally sound, even thickness ≥ 100 mm, extended ≥ 150 mm beyond wall edges for angle fillet.
• Protection:
  • Cover horizontal mastic asphalt immediately with 50 mm cement-sand screed.
  • Protect angle fillet (150 mm bitumen mastic) with 50 mm cement-sand screed over building paper.
  • After vertical damp-proofing, erect a brick wall (10 cm thick) outside for protection.
• Fig. 3 illustrates layering:
  Brick wall → Cement-sand screed (5 cm) → Structural form → Base → Hard working platform.

Internal Tanking (Clause 6.1.4)

• Excavation space: ≥ 300 mm outside wall to keep dry.
• Base slab: Even surface for damp-proofing.
• Walls: Built full height before mastic application.
• Earth filling: Only after 3 vertical mastic coats & hardened loading coats.
• Protection: After horizontal mastic & angle fillets, apply 50 mm cement-sand (1:4) screed before structural floor/walls.
• Fig. 4 layering:
  Cement-sand screed (5 cm) → Bitumen mastic angle fillet → Lean base concrete → Hard working platform.

Additional Notes

• Openings: Avoid openings in tanked walls/floors; if necessary, provide special treatment (Fig. 1).
• Mixing: Follow IS 5871-1970 for bitumen mastic mixing/remelting.

Summary Table

IS 7198 Key Specifications for Joints, Chases, and Angle Fillets

1. Joints (Clause 8.2.2 & 8.5)

• Joints in successive bitumen mastic coats must be staggered:
  • Horizontal: ≥ 150 mm
  • Vertical: ≥ 75 mm
• Construction joints:
  • Warm edges of existing mastic with hot asphalt.
  • Clean and cut with metal trowel.
  • Pour fresh mastic before surface cools.

2. Chases (Clause 8.3)

• Vertical bitumen mastic top should turn into a chase of minimum 25×25 mm unless continuing horizontally.

3. Angle Fillets (Clause 8.4)

• Apply angle fillet at internal junctions.
• Minimum width: 50 mm.
• Apply in two coats.

Summary Table:

flowchart LR
    A[Joints] --> B[Staggered: Horizontal ≥150 mm]
    A --> C[Staggered: Vertical ≥75 mm]
    A --> D[Warm & clean edges before fresh mastic]

    E[Chases] --> F[Vertical chase: 25×25 mm min]

    G[Angle Fillets] --> H[Min width 50 mm]
    G --> I[Apply in two coats]

This ensures durability and proper bonding of bitumen mastic layers as per IS 7198.

Protection of Damp-Proofing Membrane (IS 7198)

Key Specifications & Procedures

• Surface Preparation (6.1.1.6):

  • Keep surface dry during laying.
  • Follow IS 3067-1966 for laying procedures.
  • Continue dewatering until bitumen mastic hardens and structure gains strength to resist hydrostatic pressure.

• Walls & Floors Above Ground (6.1.2):

  • Damp-proofing must cover full wall thickness (excluding plaster) or base of cavity walls.
  • No setback for pointing.
  • Continuity of bitumen mastic between wall and adjacent floors is mandatory.
  • Provide vertical damp-proof course on inner wall surface (see Fig. 2).

• Externally Applied Tanking (6.1.3):

  • Minimum 0.6 m working space outside walls.
  • Provide a 100 mm thick, even, structurally sound base, extending 150 mm beyond wall edges for angle fillet (Fig. 3).
  • Cover horizontal mastic asphalt immediately with 50 mm cement-sand screed to avoid damage.
  • Protect vertical damp-proofing by erecting a 10 cm brick wall outside.
  • Protect angle fillet with 50 mm cement-sand screed over building paper.

Typical Dimensions from Figures

Summary Diagram (Fig. 3 - External Tanking Protection)

graph TD
  A[Structural Wall] --> B[Bitumen Mastic Vertical DPC]
  B --> C[10 cm Brick Wall Protection]
  C --> D[5 cm Cement-Sand Screed]
  D --> E[Hard Working Platform (Rubble Soling, Rammed Earth)]
  A --> F[100 mm Lean Base Concrete]
  F --> G[150 mm Extension for Angle Fillet]
  G --> B

Important Notes

• Maintain continuity of damp-proof

Special Treatments Around Openings and Penetrations (IS 7198)

Key Provisions:

• Avoid openings for pipes/cables in tanked walls or floors where possible (Clause 6.1.1.5).
• If essential, provide special treatment around openings as per Fig. 1:
  • Ensure continuity of tanking by sealing and wrapping the opening.
  • Use bitumen mastic or suitable waterproofing material tightly around penetrations.

Damp-Proofing in Walls and Floors Above Ground (Clause 6.1.2):

• Damp-proofing must cover full wall thickness (excluding plaster).
• Must be continuous with bitumen mastic layer in floors.
• Provide vertical damp-proof course on inner wall surface (see Fig. 2).

Externally Applied Tanking (Clause 6.1.3):

• Minimum 0.6 m working space outside walls.
• Provide a 100 mm thick sound base, extending 150 mm beyond wall edges for angle fillet (Fig. 3).
• Protect horizontal mastic asphalt with 50 mm cement-sand screed.
• Vertical damp-proofing protected by brick wall and screed.

Typical Details:

Visual Summary (Simplified):

flowchart TB
    A[Wall/Floor with Opening] --> B[Seal opening with bitumen mastic]
    B --> C[Wrap pipe/cable tightly]
    C --> D[Ensure continuity of tanking]
    D --> E[Apply vertical DPC on inner wall]
    E --> F[Externally: Provide base concrete ≥100mm]
    F --> G[Extend base 150mm beyond wall edge]
    G --> H[Apply bitumen mastic angle fillet]
    H --> I[Protect with 50mm cement-sand screed]
    I --> J[Protect vertical tanking with brick wall]

References:

• IS 7198 Clause 6