Code of practice for maintenance and preservation of stones in building
1977 Edition

Overview of IS 8759: Scope & Highlights

Scope (Clause 0.3):

• Pertains to the upkeep and protection of stones in construction, focusing on sedimentary and porous varieties, particularly those uncoated.
• Discusses main contributors to stone degradation and outlines preventive actions.
• Emphasizes practices adapted to Indian environmental conditions.
• Details cleaning approaches such as water/steam washing, sandblasting, and chemical methods (Clause 3.7).
• Refers to Indian Standards for preservatives (Appendix A), including linseed oil, coal tar, sodium silicate.

Key Details:

Preventive Strategy Flow:

flowchart TD
    X[Causes of Stone Decay] --> Y[Physical & Chemical Alterations]
    Y --> Z[Preventive Actions]
    Z --> A[Cleaning Procedures]
    Z --> B[Application of Preservatives]
    A --> C[Water/Steam Washing]
    A --> D[Sand Blasting]
    A --> E[Chemical Cleaning]
    B --> F[Linseed Oil Treatment]
    B --> G[Coal Tar Application]
    B --> H[Sodium Silicate Coating]

Note: Select durable stones initially to reduce deterioration. Testing values should follow IS 2-1960 rounding.

Primary Causes of Stone Degradation (IS 8759, Clauses 2.0 - 2.9):

• Environmental Agents: Physical and chemical alterations caused by weather exposure.
• Rain Impact (2.1): Cycles of wetting and drying induce thermal stresses and chemical erosion from acidic precipitation.
• Solar Radiation: Leads to expansion and contraction cycles, fostering crack formation.
• Pollution: Gaseous pollutants like SO2 and CO2 chemically attack stone surfaces.
• Freeze-Thaw Cycles: Water inside pores freezes and expands, causing fragmentation.
• Salt Crystallization: Accumulation and crystallization of salts exert pressure, leading to surface flaking.
• Biological Colonization: Growth of algae, fungi, and lichens secretes acids that deteriorate stone.
• Metal Fixtures (2.9): Corroding iron clamps and dowels expand, fracturing adjacent stone; anti-corrosive measures are necessary.

Preventative Recommendations:

• Utilize stones with low porosity and high durability.
• Employ protective surface coatings.
• Prevent direct iron contact or shield metal fixtures.
• Minimize moisture penetration and exposure to pollutants.

Table: Common Deterioration Mechanisms

flowchart LR
    M[Atmospheric Agents] --> N[Physical Alterations]
    M --> O[Chemical Alterations]
    N --> P[Temperature Stress]
    N --> Q[Frost Effects]
    O --> R[Acid Rain Damage]
    O --> S[Pollution Gas Effects]
    Q --> T[Cracking & Spalling]
    R --> U[Surface Erosion]
    S --> U
    V[Iron Fixtures] --> W[Rust Expansion]
    W --> T

Reference: IS 8759 guidance.

IS 8759: Effects of Rainfall on Stone Surfaces

Rain Effects (Clause 2.1):

• Alternating wet and dry conditions cause thermal stress and promote weathering.
• Rainwater, containing dissolved gases and acids, chemically attacks stones.
• Outcomes include surface loss, weakening, and aesthetic degradation.

Protective Approaches (Clause 3.3.2):

• Use of silicone-based water repellents:
  • Formulations include silicone dissolved in organic solvents or metallic siliconates such as sodium siliconate in water.
  • Upon exposure, these compounds decompose to release silicone, forming protective layers.
  • These treatments reduce water uptake and limit staining.

Design Recommendations:

• Factor in wetting/drying cycles during durability assessment.
• Apply water-repellent coatings to minimize moisture penetration.
• Incorporate adequate drainage and architectural features to shield from direct rainfall.

Conceptual Flow of Water Repellent Application:

flowchart LR
    S[Stone Surface] --> T[Silicone Solution Application]
    T --> U[Penetration into Stone]
    U --> V[Protective Layer Formation]
    V --> W[Reduced Water Absorption & Staining]

Design Considerations:

• Moisture diffusion coefficients
• Thermal expansion stresses from wetting/drying
• Chemical resistance of stone types

For detailed durability analysis, refer to IS 1121 and IS 1387.

IS 8759: Influence of Temperature Fluctuations on Stone Integrity

• Temperature variations cause cyclical heating and cooling, inducing stresses that may crack or deteriorate stones, especially in thicker masonry.
• Thin stone walls experience reduced thermal stress due to lower temperature gradients.

Key Insights (Clause 2.2):

• Ambient temperature changes generate thermal stresses impacting stone durability.
• Cracking and disintegration may result from these stresses.
• Reduced thickness in stonework helps mitigate thermal effects.

Engineering Calculation:

[ \sigma_t = E \times \alpha \times \Delta T ]

Where:

• (\sigma_t): Thermal stress (Pa)
• (E): Stone's modulus of elasticity (Pa)
• (\alpha): Coefficient of linear thermal expansion (per °C)
• (\Delta T): Temperature change (°C)

Typical values:

• (E): 5 to 50 GPa depending on stone type
• (\alpha): 5 to 12 × 10⁻⁶ /°C

Recommendations:

• Select stones with low thermal expansion and high tensile strength in climates with wide temperature ranges.
• Incorporate expansion joints or use thin stone sections where feasible.
• Surface treatments may reduce temperature-induced deterioration.

flowchart LR
    TempChange[Temperature Variation] --> Cycle[Heating & Cooling]
    Cycle --> Stress[Thermal Stresses]
    Stress --> Damage[Cracking & Disintegration]
    Damage --> Preservation[Maintenance & Protection]

Summary: IS 8759 stresses accounting for temperature-induced stresses when preserving stone structures.

IS 8759: Effects of Wind on Stone Durability

• Wind causes abrasion by carrying dust and grit particles that erode stone surfaces.

• Moisture variations driven by wind accelerate weathering, leading to stone decay.

• Porous sedimentary stones are particularly susceptible to wind-driven erosion.

• Preventive guidelines include:

  • Regular surface cleaning to remove abrasive particles.
  • Application of protective coatings or preservatives (see Appendix A).
  • Structural design considerations to minimize direct wind exposure.

Engineering Concepts (Supplementary):

• Abrasion rate is roughly proportional to wind velocity raised to a power (2 to 3) times particle concentration.

• Wind pressure used in structural design (per IS 8753/IS 875 Part 3):

  [ p = 0.6 \times V^2 \quad (kN/m^2) ]

Where (V) is wind speed in m/s.

Summary Table: Wind Effects and Mitigation

flowchart LR
    Wind[Strong Wind] -->|Carries particles| Abrasion[Abrasion on Stone]
    Wind -->|Causes moisture changes| Weathering[Accelerated Weathering]
    Abrasion --> Deterioration[Stone Damage]
    Weathering --> Deterioration
    Deterioration --> Maintenance[Required Preservation]

Summary: Wind contributes to mechanical and chemical stone wear; preventive maintenance is key.

Frost Damage According to IS 8759

Clause 2.4 Summary:

• Frost damage results when water inside stone pores freezes and expands (~9% volume increase).
• This expansion generates internal stresses that cause cracking and surface spalling.

Critical Factors Affecting Frost Damage:

• Stones with higher porosity and water absorption are more prone to frost damage.
• Expansion of freezing water exerts pressure inside pores.

Prevention Strategies:

• Use dense stones with low porosity in cold regions.
• Ensure proper drainage to avoid moisture accumulation.
• Apply water-repellent coatings and sealants to limit moisture ingress.
• Avoid iron fixtures that may rust and exacerbate damage (Clause 2.9).

Frost Pressure Model:

[ P_f = K \times E \times \alpha \times \Delta T ]

Where:

• (P_f): Frost-induced pressure
• (K): Porosity factor
• (E): Modulus of elasticity
• (\alpha): Volumetric expansion coefficient (~9%)
• (\Delta T): Temperature drop below freezing

Recommended Stone Characteristics:

Summary Diagram:

flowchart LR
    Moisture[Moisture in Pores] --> Freeze[Below Freezing Temp]
    Freeze --> Expansion[Water Expands ~9%]
    Expansion --> Stress[Internal Stone Stress]
    Stress --> Damage[Cracking & Spalling]
    Damage --> Prevention[Preventive Actions]

In summary: Dense, low-porosity stones with good drainage and protective treatments minimize frost damage.

IS 8759: Atmospheric Pollution and Stone Degradation

Key Insights (Clause 2.5):

• Urban and industrial atmospheres contain smoke and acidic gases.

• Carbonate-rich stones (limestones, calcareous sandstones) are especially vulnerable to chemical attack in such environments.

• Cleaning (Clause 3.7) is vital to remove deposits that accelerate stone decay.

• Cleaning techniques include water or steam washing, sandblasting, and chemical treatments.

• Preservatives listed in Appendix A include:

  • Linseed oil (IS 212-1961)
  • Crude coal tar (IS 1083-1975)
  • Industrial bitumen (IS 1083-1975)
  • Paraffin wax (IS 6015-1970)

Table: Stone Types and Pollution Effects

Practical Notes:

• Acid gases react with carbonate stones causing surface erosion and weakening.
• Dust and soot deposits clog pores, retain moisture, and promote deterioration.
• Protective coatings reduce permeability and chemical exposure.

flowchart LR
    Pollution[Atmospheric Pollutants] --> AcidGases[Acidic Gases & Smoke]
    AcidGases --> ChemicalAttack[Chemical Reaction with Carbonate Stones]
    AcidGases --> PhysicalDeposits[Surface Dust & Soot]
    ChemicalAttack --> SurfaceDamage[Surface Erosion & Weakening]
    PhysicalDeposits --> MoistureRetention[Moisture Build-up]
    SurfaceDamage & MoistureRetention --> Deterioration[Stone Decay]

IS 8759: Chemical Interactions Among Different Stones

Key Points (Clause 2.6):

• When limestone and sandstone are placed side by side, chemical products from limestone's reaction with CO2 and moisture can infiltrate sandstone, causing its breakdown.
• This interaction poses risks to masonry durability.

Preservative Chemicals (Clause 3.3):

• Common agents include barium hydroxide and magnesium fluosilicate.
• These react chemically to enhance stone resilience.

Cleaning Procedures (Clause 3.7):

• Necessary to remove harmful deposits accelerating deterioration.
• Methods include water/steam washing, sand blasting, and chemical cleaning.

Binding Materials (Clause 2.7):

• Some binders may chemically harm stones; compatibility must be ensured.

Relevant IS Codes (Appendix A):

Chemical Movement Flowchart:

flowchart LR
    Limestone -->|Atmospheric Reactions| ChemicalByproducts
    ChemicalByproducts -->|Penetrate| Sandstone
    Sandstone -->|Disintegrates| StoneDamage
    Preservatives -->|Protect| Stone

Caution: Avoid placing limestone adjacent to sandstone without protective measures.

IS 8759: Influence of Binding Agents on Stone Durability

Nature of Bindings (Clause 2.7):

• Certain binding substances may chemically react with or physically degrade stones.
• Compatibility testing is essential to prevent damage.

Cleaning Importance (Clause 3.7):

• Cleaning removes harmful deposits and restores aesthetics.
• Techniques include water/steam washing, sandblasting, and chemical cleaning, avoiding aggressive agents.

Preservation Strategies (Clause 3.0):

• Use preservatives to fill pores and form protective coatings.
• Chemical reactions can harden the stone surface.

Preservatives in Appendix A:

Effects & Preventive Actions:

flowchart LR
    BindingAgent --> |Impact?| ImpactType{Adverse or Neutral}
    ImpactType -->|Adverse| SelectCompatible[Choose Compatible Material]
    ImpactType -->|Neutral| Proceed[Proceed with Use]
    SelectCompatible --> ApplyPreservatives[Apply Preservatives]
    ApplyPreservatives --> FillPores[Fill Pores]
    ApplyPreservatives --> ApplyCoating[Apply Protective Coating]

IS 8759: Vegetation Effects on Stone Constructions

Highlights (Clause 2.8):

• Roots of certain trees and creepers infiltrate stone joints seeking nutrients and anchorage.
• Root growth causes physical disruption and accelerates stone deterioration.

Preventive Guidelines:

• Conduct regular inspections to identify early root intrusion.
• Remove vegetation carefully to avoid stone damage.
• Use chemical preservatives (refer Appendix A) to inhibit root growth.
• Ensure joints are tightly pointed with durable mortar to prevent ingress.

Recommendations:

Conceptual Damage Model:

• Damage ∝ Root Penetration Force × Exposure Duration

flowchart LR
    VegetationGrowth --> RootPenetration
    RootPenetration --> JointDamage
    JointDamage --> AcceleratedDecay
    Prevention --> VegetationRemoval
    Prevention --> ChemicalControl
    Prevention --> JointRepair
    VegetationGrowth -.-> Prevention

Note: While detailed root force calculations are beyond IS 8759, standard preservation practices apply.

Damage Caused by Metal Fixtures (IS 8759 Clause 2.9)

• Iron or steel clamps and dowels embedded in stone rust over time.
• Rust formation leads to expansion, causing cracking and fracturing of the stone.

Preventive Recommendations:

• Apply anti-corrosion coatings or paints on metal fixtures.
• Use corrosion-resistant materials such as stainless steel or galvanized iron when possible.
• Avoid direct contact between iron and stone by using sleeves or physical barriers.
• Perform regular maintenance and recoating to protect metal components.

Specifications:

Additional Notes:

• Use durable stones with suitable chemical and physical properties.
• Regular upkeep is critical to prevent deterioration.
• Avoid porous stones in damp locations unless adequately protected.

flowchart LR
    IronFixture --> RustFormation{Rust Occurs?}
    RustFormation -- Yes --> Expansion
    Expansion --> StoneCracking
    RustFormation -- No --> NoDamage
    AntiCorrosionCoating --> RustFormation
    UseStainlessSteel --> RustFormation

Summary: Protect iron fixtures with anticorrosive treatments and use corrosion-resistant materials to prevent rust-related stone damage.

IS 8759: Guidelines for Stone Maintenance in Buildings

Key Maintenance Procedures:

• Cleaning Techniques (Clause 3.7):

  • Water or steam washing to remove surface contaminants.
  • Sand blasting for stubborn deposits.
  • Chemical cleaning for stains and biological growth, ensuring compatibility.

• Preservatives (Appendix A):

  • Linseed oil (raw and refined)
  • Crude coal tar
  • Sodium silicate
  • Industrial bitumen
  • White oil (light technical grade)
  • Paraffin wax
  • Barium hydroxide

General Recommendations:

• Remove all substances that promote stone decay.
• Avoid harsh chemicals that might damage stone texture.
• Apply preservatives to improve durability and water resistance.

Typical Workflow:

flowchart LR
    Inspection --> Cleaning
    Cleaning --> DirtType{Type of Dirt}
    DirtType -->|Surface| WaterSteamWash
    DirtType -->|Hard Deposits| SandBlast
    DirtType -->|Stains/Biological| ChemicalClean
    WaterSteamWash & SandBlast & ChemicalClean --> Drying
    Drying --> PreservativeApplication
    PreservativeApplication --> Monitoring

Notes:

• IS 8759 does not provide specific numerical formulas.
• Follow manufacturer guidelines for preservative application.
• Maintenance intervals depend on environmental exposure.

Summary: Employ a combination of cleaning and preservation to sustain stone condition and aesthetics.

IS 8759: Surface Coating Preservatives Overview

Objective (Clause 3.0):

• Protect stones by preventing moisture and atmospheric pollutants from penetrating.
• Methods include pore filling, moisture barrier application, and chemical surface hardening.

Types of Surface Coatings (Clause 3.1):

• Coal tar, bitumen, paraffin oil, linseed oil (used pure or mixed with paint)
  • Pros: Effective protection
  • Cons: May alter appearance and require frequent upkeep
• Silicate solutions (potash or soda-based)
  • Chemically harden stone surfaces

Impregnating Preservatives (Clause 3.2):

• Silicone-based products
  • Water repellents penetrating pores
  • Applied by brushing, dipping, or spraying
• Others include polyvinyl acetate and polymethyl methacrylate

Application Recommendations:

• Apply after stone has dried under sun but before sunset for optimal penetration.
• Clean stone surfaces prior to treatment (Clause 3.7).

Relevant IS Codes (Appendix A):

Preservation Method Summary:

flowchart TD
  StoneSurface --> SunDrying
  SunDrying --> ApplyPreservative
  ApplyPreservative --> PreservationEffect

IS 8759: Use of Non-Chemical Impregnating Preservatives on Stone

Overview:

• Silicone-based products are the primary non-chemical impregnating agents.
• They penetrate capillary pores, forming a water-repellent film without altering stone chemically.
• Typically diluted in toluene or white spirit.
• Applied by brushing, dipping, or spraying.
• Also includes polyvinyl acetate and polymethyl methacrylate.
• Most effective in dry indoor environments such as museums.

Specifications:

Preservation Mechanism:

• Fills pores to block moisture ingress.
• Forms protective water-repellent film.
• Maintains natural stone appearance.

Process Flow:

flowchart LR
    StoneSurface --> CapillaryPores
    CapillaryPores --> SiliconePreservative
    SiliconePreservative --> WaterRepellentFilm
    WaterRepellentFilm --> MoisturePrevention
    MoisturePrevention --> StoneProtection

Additional Notes:

• Surface coating preservatives (Clause 3.1) may affect appearance.
• Cleaning (Clause 3.7) is essential before preservation.

Use these impregnating preservatives when maintaining stone aesthetics is a priority.

IS 8759: Chemical-Based Stone Preservatives

Highlights (Clause 3.3):

• Chemical preservatives such as barium hydroxide and magnesium fluosilicate react with stone components.
• They fill pores and create a hard, durable surface coating.

Purpose (Clause 3.0):

• To fill stone pores and prevent moisture ingress.
• To chemically enhance surface hardness and durability.

Application:

• Methods include brushing, dipping, or spraying.

Relevant IS Standards (Appendix A):

Chemical Preservative Summary:

Conceptual Reaction:

Stone components + Barium hydroxide -> Insoluble compounds -> Hard protective surface

Preservation Flow:

flowchart LR
    AtmosphericAgents --> StoneSurface[Stone Surface]
    PreservativeChemical -->|Fills pores & reacts| StoneSurface
    StoneSurface -->|Blocks| MoistureIngress
    MoistureIngress -->|Prevents| StoneDecay
    StoneDecay --> StoneProtection

Refer to specific IS codes for detailed application instructions.

IS 8759: Guidelines on Paints and Surface Coatings for Stones

Key Points:

• Painting offers protection but is discouraged for historic or monumental stones as it obscures natural texture and colour (Clause 3.4).

• Surface coatings (Clause 3.1) such as coal tar, bitumen, paraffin oil, and linseed oil (alone or with paint) are applied after sun drying, preferably before sunset.

• Silicate solutions harden stone surfaces chemically.

• These coatings may change stone appearance and require regular upkeep.

• Cleaning (Clause 3.7) is essential prior to coating application.

Recommended Preservatives (Appendix A):

Application Summary:

• Dry stone surface thoroughly under sunlight.
• Apply preservative before sunset to avoid rapid drying and cracking.
• Regular inspection and reapplication are necessary due to environmental exposure.

flowchart TD
    StoneSurface --> SunDrying
    SunDrying --> ApplyCoating
    ApplyCoating --> CoatingType{Type of Preservative}
    CoatingType -->|Coal Tar / Bitumen / Oils| AppearanceChange[Protects but alters appearance]
    CoatingType -->|Silicate Solution| SurfaceHardening[Hardens stone surface]

IS 8759: Limewash Usage in Stone Conservation

• Limewash is generally not recommended for old or historic buildings as it adversely affects their appearance (Clause 3.5).

• Despite traditional use, limewash does not effectively protect stone surfaces.

• Surface coatings (Clause 3.1) like coal tar, bitumen, paraffin oil, and linseed oil (alone or mixed) are applied after drying, preferably before sunset.

• Silicate solutions chemically harden stone surfaces.

• These treatments may alter appearance and require frequent maintenance.

• Cleaning (Clause 3.7) is necessary to restore stone and prevent deterioration.

• Relevant IS standards for preservatives are provided in Appendix A.

Summary Table: Surface Preservatives and Effects

flowchart LR
    StoneSurface --> SunDrying
    SunDrying --> ApplyPreservativeBeforeSunset
    ApplyPreservativeBeforeSunset --> PreservativeType{Type of Preservative}
    PreservativeType -->|Coal Tar / Bitumen| AppearanceChange[Alters appearance, requires upkeep]
    PreservativeType -->|Linseed Oil| AppearanceChange
    PreservativeType -->|Sodium Silicate| SurfaceHardening[Hardens surface, less impact]

IS 8759: Recommended Cleaning Methods for Stone Maintenance

Summary (Clause 3.7):

• Cleaning is crucial to restore the stone’s original look and inhibit deterioration.
• Methods include:
  • Washing with water or steam
  • Sand blasting
  • Chemical cleaning with compatible agents

Key Considerations:

• Choose cleaning technique based on stone type and dirt severity.
• Use gentle methods to avoid surface damage.
• Test chemicals on small areas before full application.
• Avoid high-pressure washing on soft or porous stones.

Related Preservatives (Appendix A):

Cleaning Process Flow:

flowchart TD
    StoneSurface --> CleaningMethod{Select Cleaning Method}
    CleaningMethod -->|Water/Steam| GentleWash
    CleaningMethod -->|Sand Blasting| HardStoneOnly
    CleaningMethod -->|Chemical| CompatibilityCheck
    GentleWash & HardStoneOnly & CompatibilityCheck --> RestoredAppearance

This approach ensures effective cleaning while preserving stone surface integrity.

IS 8759: Reference Indian Standards for Stone Preservatives

Overview (Appendix A, Clause 0.3):

• Lists relevant IS codes for commonly used preservatives in stone maintenance:

Preservation Practices (Clause 3.7):

• Cleaning stones with water/steam, sand blasting, or chemicals is essential.
• Use preservatives per the IS standards listed.

Additional Notes:

• Stone durability depends on physical and chemical stone properties.
• Use durable stones from the outset to minimize decay.
• Preservation is especially important for porous sedimentary stones.
• Follow IS 2-1960 for rounding test results.

Preservation Process Flow:

flowchart TD
    StoneDeterioration --> Cleaning
    Cleaning --> CleaningMethod{Select Method}
    CleaningMethod -->|Water/Steam| Wash
    CleaningMethod -->|Sand Blasting| Blast
    CleaningMethod -->|Chemical| ApplyPreservative
    ApplyPreservative -->|Examples| LinseedOilCoalTarBitumen
    LinseedOilCoalTarBitumen --> StoneDurabilityRestored

This framework assists in selecting appropriate preservatives and cleaning methods for effective stone maintenance.