Code of Practice for Preparation and Use of Masonry Mortars
1981 Edition

Overview of Scope

This section outlines the comprehensive code governing the preparation and application of masonry mortars, covering material definitions, mixing processes, testing protocols, and application methods.

Highlights:

• Clause 6.4: Documentation of the maximum failure load during mortar sample testing.
• Clause 2.0: Terminology corresponds with IS 6508-1972 (cement mortar testing) and IS 4305-1967 (masonry sand).
• Clause 2.1: Accuracy standards for weighing scales used in proportioning materials.
• Clause 2.2: Utilization of the Flow Table test (IS 5512-1969) to assess mortar consistency.

Key Technical Specifications:

Example Mortar Mix Ratios (Volume Basis):

flowchart LR
    Material_Weighing --> Mixing
    Mixing --> Flow_Table_Test
    Flow_Table_Test --> Mortar_Application
    Mortar_Application --> Load_Testing

This section ensures mortar quality through standardized measurement, consistency verification, and strength evaluation.

Definitions and Cross-References

• Clause 2.0: Definitions supplement those in IS 6508:1972 (cement mortar testing) and IS 4305:1967 (sand for masonry mortars).
• Flow Table Testing (Clauses 2.2 & 2.6): Refer to IS 5512:1969 for standard testing procedures assessing workability.
• Maximum Load at Failure (Clause 6.4): Critical load recorded during strength testing.

Reference Summary:

Typical Flow Table Values (IS 5512):

flowchart LR
    IS_2250_Definitions --> IS_6508
    IS_2250_Definitions --> IS_4305
    IS_2250_Definitions --> IS_5512
    IS_5512 --> Flow_Values
    Testing --> Max_Load_Record

Key Data for Mortar Preparation and Testing

1. Maximum Load at Failure

• As per Clause 6.4, the peak load during testing is recorded to validate design strength.

2. Mortar Grades and Proportioning (Clauses 1.5 & 5.3.2)

• Grade classification based on volume ratios of cement, lime, pozzolana, and sand.
• Compressive strengths at 28 days vary accordingly.

Example Mortar Grade Table

3. Reference to Flow Table Testing

• IS 5512-1969 provides flow table data crucial for consistency and workability assessments (Clause 2.2).

flowchart TD
    Start --> Select_Mortar_Grade
    Select_Mortar_Grade --> Determine_Mix_Proportions
    Determine_Mix_Proportions --> Calculate_Strength
    Calculate_Strength --> Refer_IS_2250_Tables
    Refer_IS_2250_Tables --> Record_Max_Load

Note: Site verification of mix ratios and strengths is essential per IS 2250.

Specifications for Mortar Components

Mortar Grades and Mix Ratios (Loose Volume Basis)

• Lime classifications (A-E) per IS 712:1973.
• LP-20 and LP-40 denote lime-pozzolana mixtures with 20% and 40% pozzolana respectively.
• Compressive strength tested as per Appendix A of IS 2250.

Additional Notes:

• Strength is influenced by mix ratios and curing.
• Lime-pozzolana blends enhance durability.
• Cement must comply with IS 269 (Ordinary Portland Cement).

Compressive Strength Testing Summary (Appendix A)

• Mortar cubes of 70.6 mm are tested at 28 days.

Durability and Setting Characteristics

Influential Factors (Clause 5.1.1)

• Volume changes due to setting, hardening, temperature, and moisture fluctuations.
• Crack patterns: finely dispersed cracks are preferable to large localized ones.
• Bond strength between mortar and masonry units to prevent failure and water ingress.
• Chemical resistance to environmental degradation.

Mortar Grades and Strength (Clause 5.3.2, Table 6)

• Lime classifications per IS 712.
• Pozzolana must exhibit lime reactivity of at least 4 N/mm².
• Strength tests follow Appendix A procedures.

Notes:

• Mix proportions are by loose volume.
• Strength values assume wet-ground ingredients.
• Ordinary Portland Cement per IS 269 for cement-pozzolana mortars.

flowchart LR
    Durability_Factors --> Volumetric_Changes
    Durability_Factors --> Crack_Patterns
    Durability_Factors --> Bond_Strength
    Durability_Factors --> Chemical_Resistance

Summary of Mortar Grade Classifications

Based on Clause 5.3.2 and Table 1

• Grades are identified by their 28-day compressive strength (N/mm²).
• Mix proportions are expressed in loose volume of cement, lime, pozzolana, and sand.
• Lime-pozzolana blends (LP-20, LP-40) are used in some mixes.

Common Mortar Grades and Mix Ratios

Additional Information:

• LP mixtures denote lime-pozzolana ratios.
• Strength testing per Appendix A.
• Lime classes correspond to IS standards.
• Proportions vary based on strength and application needs.

Testing Methodology

• Compression strength is measured on mortar cubes after 28 days curing.

flowchart LR
    Raw_Materials --> Cement
    Raw_Materials --> Lime
    Raw_Materials --> Pozzolana
    Raw_Materials --> Sand
    Cement & Lime & Pozzolana & Sand --> Mix_Proportioning
    Mix_Proportioning --> Strength_Testing

Selection Criteria for Masonry Mortars

Summary from Clause 7.1 and Table 1

• Mortar selection is influenced by structural loading and environmental exposure.
• Grades classify mortar by minimum 28-day compressive strength.
• Mix proportions are specified as loose volume of cement, lime, pozzolana, and sand.
• Lime classifications follow IS 712.
• Pozzolana should have minimum lime reactivity of 4 N/mm².

Simplified Grade Table

Important Notes

• LP mixtures indicate lime-pozzolana volume ratios.
• Compressive strength testing follows Appendix A.
• Ordinary Portland Cement should meet IS 269 standards.

Approximate Cement-Pozzolana Weight Ratio:

[ \text{Cement} : \text{Pozzolana} \approx 0.8 : 0.2 ]

flowchart TD
    Loading_Conditions & Exposure --> Mortar_Grade_Selection
    Mortar_Grade_Selection --> Mix_Proportions
    Mix_Proportions --> Strength_Requirements
    Strength_Requirements --> Durability_Considerations

Mortar Preparation Essentials

Mortar Grades and Mix Proportions (Table 1, Clauses 5.3.2 & 6.1)

Mortars are categorized based on minimum 28-day compressive strength with mix ratios by loose volume:

• Lime classifications per IS 712-1973.
• Pozzolana requires minimum lime reactivity of 4 N/mm².
• Strength testing per Appendix A.

Unit Weights for Volume-Weight Conversion (Table 2, Clause 8.1.1)

• Loose condition refers to poured material without compaction.

Additional Notes:

• Strength depends on wet grinding of ingredients.
• Cement-pozzolana volume ratio ~0.8:0.2 corresponds to weight ratio.
• Ordinary Portland Cement must conform to IS 269-1976.

Summary Expression for Mortar Mix by Loose Volume:

[ \text{Mortar Mix} = \text{Cement} + \text{Lime} + \text{Pozzolana} + \text{Sand} ]

Key Aspects of Mortar Consistency and Workability

Consistency (Clauses 2.5, 9.1)

• Determined by practical assessment during masonry application.
• Must retain sufficient fluidity for easy spreading without segregation.
• Water content considerations:
  • Masonry unit type affects absorption (e.g., burnt clay, concrete blocks require good water retention).
  • Joint thickness influences fluidity requirements.
  • Load-bearing joints may require stiffer mixes.
• Water retention is critical to prevent rapid absorption.

Workability (Clause 2.9)

• Refers to ease of mixing, placing, compacting, and finishing.
• Related to the internal friction and energy required for consolidation.

Re-Tempering (Clause 8.6.1)

• Water addition to stiffened mortar is permissible within 60 minutes of cement introduction to restore workability.

Typical Water Content Guidelines

Water Content Formula:

[ W = f(\text{unit absorption}, \text{joint thickness}, \text{desired fluidity}) ]

Where W = water quantity in liters per 50 kg cement.

flowchart LR
    Mix_Mortar --> Assess_Consistency
    Assess_Consistency -->|If too stiff| Add_Water
    Assess_Consistency -->|If too fluid| Add_Dry_Mix
    Add_Water --> Apply_Mortar
    Add_Dry_Mix --> Apply_Mortar
    Apply_Mortar --> Achieve_Workability

IS 2250 prioritizes practical judgment for achieving suitable consistency on-site.

Sampling Guidelines for Fresh Mortar Batches

Clause 10 Overview

• Collect representative samples immediately after mixing using clean, uncontaminated containers.
• Mark samples with details including sampling location, date, and batch size.

Water Retentivity Testing (Clauses 9.2 & Appendix C)

• Important for masonry with high suction properties.
• Water retentivity requirement:

[ \text{Flow after suction} \geq 70% \times \text{Flow before suction} ]

Mortar Grades and Mix Proportions (Table 1, Clause 5.3.2)

flowchart TD
    Fresh_Mortar --> Sample_Immediately
    Sample_Immediately --> Label_And_Record
    Label_And_Record --> Perform_Tests
    Perform_Tests --> Water_Retentivity_And_Strength

Refer to Appendix A for compressive strength and Appendix C for water retention tests.

Compressive Strength Determination Procedure

Clause 6.1 and Related

• Mortar grades are defined by minimum compressive strength at 28 days.
• Testing follows procedures specified in Appendix A.
• Mix proportions by loose volume of cement, lime, pozzolana, and sand.

Notes:

• Lime classes per IS 712:1973.
• Pozzolana reactivity ≥4 N/mm².
• Wet grinding improves strength.
• Cement-pozzolana ratio approx. 0.8:0.2 by weight.

Testing Steps:

• Prepare mortar cubes (70.6 mm).
• Cure for 28 days under standard conditions.
• Test using compression machine.
• Calculate compressive strength:

[ f_c = \frac{P}{A} ]

Where:

• ( f_c ): compressive strength (N/mm²)
• ( P ): maximum load at failure (N)
• ( A ): cross-sectional area (mm²)

flowchart TD
    Prepare_Mix --> Cast_Cubes
    Cast_Cubes --> Cure_28_Days
    Cure_28_Days --> Compression_Test
    Compression_Test --> Calculate_Strength

Consistency Testing Procedure

Clauses Referenced:

• Clauses 1.1, B-1.1, 9.1.1, and 4.1
• Appendix B outlines the flow table or flow cone test methods.
• Clause 8.1 and Appendix C relate to water retention impacting consistency.

Test Description:

• Objective: Identify water content at which mortar achieves standard flow.
• Prepare mortar batches with varying water quantities.
• Conduct flow table test measuring flow diameter or time.
• Average two readings for consistent results.

Typical Flow Table Results

Optimum consistency corresponds to flow diameter ~110 mm.

Water Retentivity Importance

• Measures mortar's ability to retain moisture for proper hydration and bonding.

flowchart LR
    Prepare_Mortar --> Add_Water_Variations
    Add_Water_Variations --> Test_Flow
    Test_Flow --> Measure_Diameter
    Measure_Diameter --> Is_Flow_110mm
    Is_Flow_110mm -- Yes --> Report_Consistency
    Is_Flow_110mm -- No --> Adjust_Water

Determining Water Retentivity (Appendix C)

Purpose

• To quantify mortar’s capacity to retain water against suction and evaporation, critical for use with high-absorption masonry units.

Specification

• Post-suction flow must not be less than 70% of initial flow.

Test Summary

1. Prepare fresh mortar and place on standard flow table.
2. Measure initial flow (before suction).
3. Apply specified suction.
4. Measure flow after suction.
5. Calculate water retentivity:

[ \text{Water Retentivity} = \frac{\text{Flow after suction}}{\text{Flow before suction}} \times 100% ]

Acceptance Criteria

• Water Retentivity ≥ 70%

Flow Table Dimensions

flowchart LR
    Prepare_Sample --> Place_on_Flow_Table
    Place_on_Flow_Table --> Measure_Initial_Flow
    Measure_Initial_Flow --> Apply_Suction
    Apply_Suction --> Measure_Flow_After_Suction
    Measure_Flow_After_Suction --> Calculate_Retentivity
    Calculate_Retentivity --> Is_Retentivity_Above_70
    Is_Retentivity_Above_70 -- Yes --> Approve_Mortar
    Is_Retentivity_Above_70 -- No --> Adjust_Mix

Note: This test indirectly assesses mortar’s workability and water retention capability, essential for bond durability.