Subhead 3.0: Mortars

Subhead 3.0: Mortars

Subhead 3.0 focuses on the materials, preparation, and specifications of various types of mortars used in construction. Below is a detailed explanation of each section along with examples.

3.0 General

Desirable properties of mortars for use in masonry are:

• Workability: The ability to be easily spread and worked with.
• Water Retentivity: The ability to retain water during the setting process.
• Rate of Stiffening: How quickly the mortar sets and hardens.
• Strength: The compressive strength of the mortar.
• Resistance to Rain Penetration: The ability to resist water ingress.
• Durability: The longevity and performance of the mortar under various conditions.

Example: A mortar mix used for external walls needs to be durable and resistant to rain penetration to prevent water damage and ensure longevity.

3.1 Materials

3.1.1 Water

• Quality: Water used for mixing and curing must be clean and free from harmful substances. Potable water is generally satisfactory.
• pH Value: Should not be less than 6.
• Limits: Maximum permissible limits for acidity, alkalinity, and solids such as chlorides, sulphates, and organic/inorganic solids.
• Testing: Water should be tested before the commencement of work and periodically thereafter.

Example: Using potable water with a pH of 7 for mixing mortar ensures no detrimental effects on the setting and strength of the mortar.

3.1.2 Cement

• Types: Different grades and types of cement can be used, such as ordinary Portland cement, rapid hardening Portland cement, Portland slag cement, and more.
• Storage: Cement should be stored in a dry, leakproof shed, stacked on wooden planks to avoid contact with the floor, and protected from moisture.

Example: Using 43 grade ordinary Portland cement conforming to IS 8112 for general masonry work ensures adequate strength and durability.

3.1.3 Fine Aggregate

• Types: Fine aggregate includes natural sand, crushed stone sand, crushed gravel sand, stone dust, marble dust, fly ash, and broken brick.
• Quality: Must be hard, durable, clean, and free from harmful impurities.
• Grading: Fine aggregate is graded into four zones based on particle size.

Example: Fine aggregate passing through a 4.75 mm sieve and conforming to grading zone IV is suitable for use in plaster work.

3.1.4 Surkhi (Crushed Brick Aggregate)

• Properties: Should be hard, durable, and free from impurities.
• Storage: Should be stacked on a hard surface and protected from rain and dampness.

Example: Using surkhi for mortar mix in heritage building restoration to match the original materials.

3.1.5 Fly Ash

• Types: Siliceous fly ash and calcareous fly ash, with different properties and uses.
• Characteristics: Must meet specific physical and chemical requirements as per IS 3812.
• Storage: Protected from contamination and dirt.

Example: Using fly ash in mortar mix to improve workability and reduce the heat of hydration.

3.2 Preparation of Mortars and Its Grade

3.2.0 Grade of Masonry Mortar

• Definition: Defined by its compressive strength at 28 days as per IS 2250.
• Proportioning: Conversion of weight into volume based on specific gravity.

Example: A mortar with a compressive strength of 3 N/mm² at 28 days is classified as MM 3 grade.

3.2.1 Cement Mortar

• Proportioning: Preferred to be done by weight, considering the specific gravity of sand and moisture content.
• Mixing: Can be done using mechanical mixers or by hand with approval.
• Precautions: Mortar should be used within 30 minutes of mixing to prevent setting.

Example: Mixing cement and sand in a 1:6 ratio by weight to prepare mortar for bricklaying.

3.2.2 Cement Flyash Sand Mortar

• Proportioning: Similar to cement mortar but includes fly ash.
• Mixing: Preferably done in mechanical mixers unless otherwise approved.

Example: Using a 1:4:3 ratio of cement, fly ash, and sand for preparing mortar to reduce the overall cost and improve workability.

Appendices

• Appendix A: Test for Organic Impurities
• Appendix B: Test for Particle Size (Sieve Analysis)
• Appendix C: Test for Silt Content
• Appendix D: Bulking of Fine Aggregates/Sand (Field Methods)
• Appendix E: Physical Requirements of Fly Ash
• Appendix F: Criteria for Selection of Masonry Mortars

Summary

Subhead 3.0 covers the specifications for the materials and preparation of various types of mortars used in construction. It ensures that the right materials are used in the correct proportions to achieve the desired properties and performance of the mortar. Proper testing and quality control measures are emphasized to maintain the standards and durability of the construction work.

Thu Aug 1, 2024