Handbook on Causes and Prevention of Cracks in Building

Scope of IS SP Part 25: Causes and Prevention of Cracks in Buildings

• Thermal Movement is a key factor influencing cracks, depending on:

  • Temperature variation (ΔT)
  • Material dimensions (L)
  • Coefficient of thermal expansion (α)
  • Other physical properties

• Thermal Expansion Formula:

  [ \Delta L = \alpha \times L \times \Delta T ]

  where:

  • (\Delta L) = change in length
  • (\alpha) = coefficient of thermal expansion (per °C)
  • (L) = original length
  • (\Delta T) = temperature change in °C

• Coefficient of Thermal Expansion for Common Materials (×10⁻⁶ /°C):

  Material	α (×10⁻⁶ /°C)
  Bricks and brickwork	5 to 7
  Cement mortar and concrete	10 to 14
  Sand-lime bricks	11 to 14
  Granite (Igneous rocks)	8 to 10
  Limestone	2.4 to 9
  Marble	1.4 to 11
  Sandstones	7 to 16
  Aluminium	25
  Steel and iron	11 to 13

• Scope includes:

  • Causes of cracks: moisture, thermal, elastic deformation, creep, chemical reactions, foundation movement, vegetation.
  • Prevention and remedial measures.
  • Guidelines for diagnosis and repair.

• Reference Sections:

  • Section 3: Thermal Movement
  • Section 10: Summary of Prevention Measures

This handbook aids architects, engineers, and builders in minimizing cracks by understanding material behavior and environmental effects.

Material Properties Influencing Cracking (IS SP Part 25, Clause 10.2.1)

Key properties affecting cracking include:

• Drying shrinkage
• Moisture movement
• Thermal expansion
• Modulus of elasticity
• Porosity
• Creep
• Thermal conductivity, insulation, capacity
• Reflectivity
• Chemical composition

Key Table: General Precautions to Avoid Shrinkage Cracks (Clause 2.5.10)

Important Notes:

• Burnt clay bricks should be air-exposed for 2 weeks in summer, 3 weeks in winter before use to avoid initial expansion cracks.
• Construction joints in concrete require careful design to avoid shrinkage cracks.

Formula for Thermal Strain (affects cracking):

[ \varepsilon_{thermal} = \alpha \Delta T ] where:

• (\alpha) = Coefficient of thermal expansion (per °C)
• (\Delta T) = Temperature change (°C)

Summary of Measures to Minimize Cracks:

• Use materials with low shrinkage and moisture movement.
• Proper curing and drying before finishing.
• Provide control joints to accommodate movement.
• Protect moisture-sensitive materials by coatings.
• Design joints and fixings to allow for expansion/contraction.

flowchart TD
    A[Material Properties] --> B[Drying Shrinkage]
    A --> C[Moisture Movement]
    A --> D[Thermal Expansion]
   

Thermal Movement and Its Effects (IS SP Part 25)

Key Formula for Thermal Movement:

[ \Delta L = \alpha \times L \times \Delta T ]

• (\Delta L) = Change in length (mm)
• (\alpha) = Coefficient of thermal expansion (per °C)
• (L) = Original length (mm)
• (\Delta T) = Temperature change (°C)

Coefficient of Thermal Expansion (×10⁻⁶ /°C)

Reflectivity Coefficients (Influence Thermal Gain)

Important Considerations:

• Thermal gradients cause warping/cracking, especially in low conductivity materials like concrete.
• Protective layers (e.g., reflective coatings, insulating layers) reduce heat gain and thermal

Elastic Deformation & Structural Stresses (IS SP Part 25)

Key Concepts (Clause 5.1 & 4.1)

• Elastic strain (e₁): Instantaneous deformation under load (Hooke's Law).
• Creep strain (e₂): Time-dependent deformation including delayed elastic recovery and permanent viscous strain.
• Total strain = Elastic strain + Creep strain.

Elastic Deformation Formula (Hooke's Law):

[ \sigma = E \cdot \varepsilon ]

• (\sigma) = Stress
• (E) = Modulus of Elasticity
• (\varepsilon) = Strain (deformation/original length)

Creep Phenomenon (Fig. 29 Summary):

• Instantaneous elastic strain (e_i)
• Time-dependent creep strain (e_2)
• Recovery strains (e_s) (instantaneous) and (e_x) (delayed)
• Permanent viscous strain (e_p) remains after unloading

Movement Joints (Clause 3.11.5 & Table 5)

Cracking in Masonry and Brickwork: Key IS Code Guidelines (IS SP Part 25)

1. Causes & Minimization (Clause 5.10.1)

• Use low shrinkage, low slump concrete.
• Avoid fast construction pace.
• Delay brickwork over flexural RCC members by ≥ 2 weeks after centering removal.
• Defer brickwork adjoining RCC columns.
• Allow ≥ 1 month for initial shrinkage and creep before plastering RCC + brickwork.
• Use grooves or 10 cm metal mesh at RCC-brickwork junctions for plaster reinforcement.
• For deflecting RCC members, defer load application by ≥ 1 month.

2. Movement Joints (Clause 1.5 & Table 5)

• Provide vertical expansion joints 5-8 mm wide at 5-8 m intervals.
• For slabs/beams supporting partitions, provide horizontal expansion joints filled with mastic.
• Use telescopic anchorage for lateral support allowing vertical movement but resisting horizontal shear.

3. Shrinkage Crack Control (Clause 2.5.10, Table 2)

4. Crack Width Limits (Clause 10.5)

• Flexural cracks in concrete:
  • 0.30 mm for protected internal members
  • 0.20 mm for unprotected external members

Summary Diagram: Crack Minimization Strategy

flowchart TD
    A[Start Construction] --> B{Use Low Shrinkage Concrete?}
    B -- Yes --> C[Slow Construction Pace]
    B -- No --> D[Risk of Cracking ↑]
    C --> E[Delay Brickwork on RCC ≥

Key Points from IS SP Part 25 on Carbonation, Corrosion, and Chemical Effects

1. Carbonation (Clause 6.3)

• Calcium hydroxide in concrete reacts with CO₂ → forms calcium carbonate, reducing alkalinity and protective effect.
• Depth of carbonation in dense concrete: ≤ 20 mm in 50 years; in porous concrete: up to 100 mm.
• Carbonation is faster in dry atmosphere but corrosion needs moisture (wet-dry cycles accelerate corrosion).
• Adequate cover and dense concrete reduce carbonation risk.

2. Corrosion of Reinforcement (Clause 3.5 & 6.3.1)

• Corrosion cells form due to differences in moisture, oxygen, electrolyte concentration, or dissimilar metals.
• Moisture presence (RH > 75%) and chloride ingress (especially from seawater) promote corrosion.
• Minimum cover as per IS 456:1978 is essential; increase cover in aggressive environments.
• Electrolysis (stray DC currents) can cause rapid corrosion.

3. Chemical Effects

• Sulphate attack: Causes expansion, cracking, and corrosion.
• Alkali-Aggregate Reaction (AAR): Weakens concrete and causes cracks.
• Impurities in mixing/curing water limits (IS 456:1978):

• Sea water use is not recommended for reinforced concrete except if permanently submerged.

Summary Table: Factors Affecting Corrosion

Key Points on Foundation and Soil Related Cracks (IS SP Part 25)

1. Causes of Foundation Cracks (Clause 7.1)

• Differential settlement due to:
  • Unequal bearing pressure under different parts.
  • Bearing pressure exceeding soil safe bearing capacity.
  • Low factor of safety in foundation design.
  • Local soil variability not accounted for in design.

2. Prevention Measures

• Design foundations based on sound engineering principles considering soil variability.
• Ensure safe bearing capacity is not exceeded.
• Provide adequate factor of safety in foundation design.
• Conduct thorough soil investigation to detect variations.

3. Vegetation Related Cracks (Clause 8.5)

• Avoid planting trees close to foundations, especially on shrinkable clay soils.
• Remove saplings growing in wall fissures immediately.
• If vegetation is removed from shrinkable clay soil, allow soil to stabilize after moisture absorption before construction.

4. General Formula for Safe Bearing Capacity (IS 6403)

[ q_{safe} = \frac{q_{ult}}{FS} ]

• (q_{ult}) = ultimate bearing capacity (kN/m²)
• (FS) = factor of safety (typically 2.5 to 3)

5. Monitoring Cracks (Appendix A)

• Use crack width gauges or tell-tales to monitor crack progression.
• Record measurements periodically for diagnosis.

Summary Table: Causes and Prevention of Foundation Cracks

flowchart TD
    A[Soil Investigation] --> B[Determine Bearing Capacity]
    B --> C{Is Bearing Pressure < Safe Bearing Capacity?}
    C -- Yes --> D[Design Foundation]
    C -- No --> E[Redesign or Soil Improvement]
    D --> F[Construct Foundation]
    F --> G[Monitor Cracks]
    G --> H{Cracks Detected?}
    H -- Yes --> I[Remedial Measures]
    H -- No --> J[Regular

Movement Joints: Types and Provisions (IS SP Part 25)

Key Provisions (Clause 3.11, 10.7.1, Table 5)

• Purpose: To accommodate thermal expansion, shrinkage, and differential movement, preventing cracking.

Types of Movement Joints

Additional Guidelines

• Control joints spacing: 3 to 5 m (transverse direction in pavements).
• Panel shape: Prefer square panels to reduce shrinkage cracking.
• Joints in plaster: 10 mm wide grooves at wall-ceiling junctions.
• Seismic zones (III, IV, V): Use wider joints per IS 4326-1976.
• Slip joints: For RCC slabs >4-6 m, 12 mm gap between slab and bearing wall.

Typical Joint Details

flowchart LR
    A[Wall] -->|Twin walls or beam| B[Expansion Joint (20-40 mm)]
    C[RCC Slab] -->|Expansion Joint (10-15 mm)| D[

Types of Cracks in Building Components & Their Causes (IS SP:25 - 1984)

Key Crack Types:

• Tensile Cracks: Caused by direct tension exceeding material tensile strength (e.g., masonry walls).
• Shear Cracks: Result from shear stresses, often near beam supports or load transfer zones.
• Shrinkage Cracks: Due to moisture loss causing volume reduction.
• Thermal Cracks: Result from temperature variations causing expansion/contraction.
• Settlement Cracks: From foundation movement or soil settlement.
• Chemical Reaction Cracks: Due to reactions like alkali-aggregate in concrete.
• Creep & Elastic Deformation Cracks: Long-term deformation under sustained loads.

Causes Summary (Clause 1.8):

• Moisture changes
• Thermal variations
• Elastic deformation
• Chemical reactions
• Foundation movement and soil settlement
• Vegetation effects

Typical Crack Identification (Fig. 1-4 in SP:25):

Prevention Measures (Summary from Section 10):

• Control moisture ingress and curing
• Provide expansion joints for thermal movement
• Use proper reinforcement detailing to resist tensile/shear stresses
• Ensure uniform and adequate foundation support
• Use chemical-resistant materials or additives
• Monitor and repair early signs of cracking

Monitoring Crack Movement (Appendix A):

• Use crack gauges or tell-tales
• Regular visual inspection and measurement

flowchart TD
    A[Causes of Cracks] --> B[Moisture Changes]
    A --> C[Thermal Variations]
    A --> D[Elastic Deformation]
    A --> E[Chemical Reactions]
    A --> F[Foundation Movement]
    A --> G[Vegetation Effects]

    B --> H[Tensile & Shrinkage Cracks]
    C --> I[Thermal Cracks]
    D --> J[Elastic & Creep Cracks]
   

Architectural Design Considerations Affecting Cracks (IS SP Part 25)

Key Factors (Clause 10.4 & 10.5)

• Large spans, large windows, short return walls increase cracking risk due to uneven strain.
• Door/window frames: Should NOT be flush with plaster; if unavoidable, use moulding strips or design as per Fig. 10.
• Uniform stress distribution in masonry walls avoids differential strain and shear cracks.
• Flexural members (slabs/beams) must have adequate stiffness to limit deflection.
• Crack width limits (Clause 6.4.3(a)):
  • Internal protected members: ≤ 0.30 mm
  • External unprotected members: ≤ 0.20 mm
• Rigid structures require thermal/shrinkage stress considerations since movement joints aren't feasible.

Shrinkage Crack Control (Table 2, Clause 2.5.10)

Fig. 10 Summary (Door Frame Fixing)

• Provide 10 mm groove between frame and half-brick masonry wall.
• Conceal joints with architraves or moulding strips to accommodate movement and prevent cracks.

Crack Width Control Formula (IS 456 Reference)

[ w_{max} = \frac{K \cdot \epsilon \cdot d}{f_{ct}} ]

• (w_{max}): Maximum crack width (mm)
• (K): Constant depending on exposure and member type
• (\epsilon): Strain in steel or concrete
• (d): Effective depth (mm)
• (f_{ct}): Tensile strength of concrete (MPa)

flowchart TD
    A[Architectural Design] --> B

IS SP Part 25: Repair & Remedial Measures for Cracks in Masonry Walls

Key Points from Clause 9.6 (Repair of Cracks):

• Diagnosis: Identify crack causes (moisture, thermal, elastic, creep, chemical, foundation movement, vegetation).
• Assessment: Monitor crack width, length, and propagation over time.
• Repair Methods:
  • Injection: Epoxy or cementitious grout for fine cracks.
  • Stitching: Steel bars across cracks for structural cracks.
  • Surface Treatment: Plaster or sealants for non-structural cracks.
  • Rebuilding: Partial dismantling and reconstruction if severe.

Clause 5.10 (Avoidance of Cracks):

• Use proper mix design to minimize shrinkage.
• Control curing to reduce moisture loss.
• Provide adequate joints to accommodate elastic strain and creep.
• Use reinforcement to control crack widths.

Typical Crack Width Limits (IS 456 & related codes):

General Preventive Measures:

• Avoid planting trees near foundations (Clause 8.5).
• Stabilize shrinkable soils before construction.
• Provide proper drainage and moisture barriers.

Summary Table: Crack Repair Techniques

flowchart TD
    A[Identify Crack Type] --> B{Crack Width}
    B -->|<0.3 mm| C[Injection Repair]
    B -->|>0.3 mm| D[Structural Repair]
    D --> E[Stitching]
    D --> F[Partial Rebuilding]
    A --> G[Non-Structural Surface Cracks]
    G --> H[Surface Treatment

Special Cases: Glass Panes, Tiles, and Precast Components (IS SP Part 25)

1. Glass Panes & Glass Blocks (Clause 9.13)

• Causes of cracking in glass panes:
  • Uneven back-putty in rebates → rattling & cracking.
  • Inadequate uniform clearance (3-4 mm) → thermal expansion stress, especially in steel windows.
  • Rusting & thermal expansion of steel frames.
• Remedies:
  • Replace cracked panes.
  • Apply back-putty uniformly.
  • Clean rust, provide uniform clearance.
  • Use sun-shading to reduce heat.
• Glass blocks:
  • Cracks due to lack of expansion provision and direct sun exposure.
  • Provide adequate expansion joints and shading.

2. Thermal Expansion (Clause 3.3, Table 3)

• Thermal expansion formula:

[ \Delta L = \alpha \times L \times \Delta T ]

Where:
(\Delta L) = change in length,
(\alpha) = coefficient of thermal expansion,
(L) = original length,
(\Delta T) = temperature change.

3. Precautions for Shrinkage and Cracking (Clause 2.5.10, Table 2)

• Use well-burnt bricks.
• Avoid rich cement mortars with moisture-sensitive stones.
• Provide control joints in sandstone masonry.
• Season timber properly; avoid flush fixing of door/window frames.
• Protect asbestos cement sheets by painting both surfaces.
• For concrete and mortar, ensure proper curing and construction joints.

Summary Diagram: Glass Pane Fixing & Thermal Expansion

flowchart LR
    A[Glass Pane] --> B[Uniform Back-putty in rebate]
    A --> C[3-4 mm Clearance around pane]
    C --> D

IS SP 25 (1984) - General Guidelines for Prevention of Cracks:

Key Points from Clause 5.10 & Table 2.5.10:

1. Shrinkage Crack Prevention Measures:

2. Additional Notes:

• Brick masonry: Expose burnt clay bricks to atmosphere for 2 weeks (summer) and 3 weeks (winter) before use to avoid initial expansion cracks.
• Door frame fixing: Avoid flush fitting on both sides; use architrave or special frame shapes (see Fig. 10).

Summary of Crack Prevention Measures:

• Proper curing and drying of masonry and concrete.
• Avoid rich mortars with materials prone to shrinkage.
• Use control joints to accommodate movement.
• Protect moisture-sensitive materials by painting or surface treatment.
• Season timber and avoid flush fittings that restrict movement.

flowchart TD
    A[Material Selection] --> B{Moisture Movement}
    B -->|Small| C[Use well burnt bricks, light mortar]
    B -->|Appreciable| D[Control joints + careful mortar choice]
    B -->|Considerable| E[Protect surfaces + avoid flush fitting]
    C --> F[Proper curing & drying]
    D --> F
    E --> F
    F --> G[

IS SP Part 25: Appendices & Illustrative Examples - Key Highlights

This handbook focuses on causes and prevention of cracks in buildings, with detailed appendices and examples for practical understanding.

Key Tables & Formulas:

1. Coefficient of Thermal Expansion (Table 3)

• Thermal movement ΔL = α × L × ΔT
  Where:
  α = coefficient of thermal expansion,
  L = original length,
  ΔT = temperature change.

2. Joints Spacing (Table 5)

• Joints are critical to accommodate movements due to thermal changes, moisture, creep, and elastic deformation.
• Spacing depends on material properties, temperature variation, construction season, structure size, and exposure.

Appendices Include:

• Appendix A: Monitoring and measuring crack movements.
• Diagnosis and repair guidelines for various crack types.
• Summary of preventive measures.

Summary:

• Use coefficients of thermal expansion to estimate dimensional changes.
• Provide adequate joints per Table 5 to avoid cracks.
• Follow diagnostic and repair procedures in appendices for maintenance.

flowchart LR
    A[Temperature Change ΔT] --> B[Thermal Expansion]
    B --> C[Length Change ΔL = α × L × ΔT]
    C --> D[Joints to Accommodate ΔL]
    D --> E[Prevention of Cracks]

For detailed tables and examples, refer to IS SP Part 25 full handbook.