Mortar is an essential building material used in construction to bind bricks, stones, and other masonry units, ensuring structural integrity and stability. Depending on the binding material used, mortars exhibit distinct properties, making them suitable for a wide range of applications in construction. Each type of mortar is designed to cater to specific structural requirements and environmental conditions. This section provides a detailed exploration of the various types of mortars, focusing on their composition, characteristics, advantages, and applications.
Common Types of Mortar
1. Lime Mortar
Lime mortar is a type of mortar where fat lime or hydraulic lime acts as the binding material. The lime must be slaked properly before use to ensure the desired performance.
The type of lime used significantly affects the properties and performance of the mortar. Fat lime, due to its high shrinkage during the setting process, requires a larger proportion of sand—typically 2–3 times its volume—to minimize cracking and achieve stability. In contrast, hydraulic lime hardens more effectively in damp conditions, offering improved durability and making it more suitable for a wider range of applications.
Advantages of Lime Mortar
- Workability: Lime mortar is highly plastic and easy to work with, making it ideal for detailed and intricate masonry work.
- Cohesiveness: Exhibits excellent cohesiveness and adhesion to surfaces, ensuring strong bonding.
- Shrinkage: Undergoes minimal shrinkage compared to other mortars, reducing the risk of cracks.
Limitations of Lime Mortar
- Durability: While lime mortar is reasonably durable, it hardens slowly, which may extend construction timelines.
- Water Resistance: Not suitable for waterlogged or damp environments as it lacks sufficient resistance to moisture.
Applications of Lime Mortar
- Primarily used in lightly loaded structures due to its moderate strength.
- Preferred for above-ground construction, such as walls and masonry in dry conditions.
- Common in historic restoration projects where maintaining original material properties is essential.
2. Surkhi Mortar
Surkhi mortar is a specialized type of mortar prepared by mixing lime with surkhi (powdered burnt clay) as a partial or complete replacement for sand. When using fat lime, only about 50% of the sand needs to be substituted with surkhi to maintain the desired performance. It is crucial that the surkhi is finely powdered to ensure proper mixing and bonding.
Characteristics of Surkhi Mortar
- Composition: A blend of lime and surkhi, with fat lime requiring partial sand replacement for improved stability.
- Workability: Surkhi mortar is easy to handle but requires careful preparation to ensure uniformity.
- Durability: While suitable for general masonry, surkhi’s tendency to disintegrate limits its use in applications exposed to wear or moisture.
Applications of Surkhi Mortar
- Primarily used for ordinary masonry work in structures with moderate load requirements.
- Not recommended for pointing work or plastering, as the surkhi particles may break down over time, affecting surface finishes and durability.
Surkhi mortar is an economical and efficient choice for basic construction needs, especially in regions where surkhi is readily available, but its limitations must be considered during planning and application.
3. Cement Mortar
Cement mortar is a widely used construction material where cement serves as the binding material. Its performance is determined by the mix proportion of cement to sand, as well as the resulting compressive strength after 28 days of curing. To standardize its application, cement mortars are categorized into grades based on these parameters.
Grades of Cement Mortar and Their Properties
The following table summarizes commonly used grades, their mix proportions, and compressive strengths:
| Grade | Mortar Mix (Cement : Sand) | Compressive Strength at 28 Days (N/mm²) |
|---|---|---|
| MM 1.5 | 1:7 | 1.5 to 2.0 |
| MM 3.0 | 1:6 | 3.0 to 5.0 |
| MM 5.0 | 1:5 | 5.0 to 7.5 |
| MM 7.5 | 1:4 to 1:3 | 7.5 and above |
Note: MM denotes Masonry Cement Mortar.
Recommended Uses of Cement Mortar Grades
Different grades of cement mortar are suited to specific construction tasks:
- MM 2: For external works with protection and foundation masonry in very wet soils.
- >MM 2: For external walls without additional protection.
- MM 3: Suitable for foundation masonry in saturated soils and masonry subjected to vibrations.
- MM 5 to MM 7.5: Recommended for plastering works.
- MM 7.5: Ideal for floor finishes and damp-proof courses.
Applications of Cement Mortar
Cement mortar is versatile and used across a wide range of construction activities, including:
- Brick and Stone Masonry: Provides strength and stability to masonry structures.
- Plastering: Applied to surfaces like walls, beams, and columns to ensure a smooth finish.
- Floor Finishes: Offers durability and smoothness for floors.
- Binding Material for Decorative Works: Used in aesthetic and ornamental construction.
- Pointing: Enhances the appearance and durability of brick and stone masonry joints.
- Load Distribution: Levels irregular surfaces of stone masonry, enabling uniform load distribution on the bed.
- Underground Construction: Ideal for applications in water-saturated soils and below-ground structures.
Cement mortar’s versatility, strength, and ease of use make it indispensable in modern construction practices. Its selection and application depend on the specific requirements of the project, ensuring both structural integrity and longevity.
4. Lime–Cement Mortar
Also referred to as Gauged Mortar or Composite Mortar, lime–cement mortar is a blend that combines the workability and plasticity of lime with the strength and durability of cement. By adding cement to lime mortar, the mixture gains improved early strength, making it both economical and efficient for construction.
Composition and Proportion of Lime–Cement Mortar
The typical proportion of cement to lime by volume ranges from 1:6 to 1:8, depending on the desired strength and application. This balance ensures that the mortar retains the smooth handling properties of lime while benefiting from the rapid setting and hardness provided by cement.
Advantages of Lime–Cement Mortar
- Improved Strength: The addition of cement enhances the compressive strength and durability of lime mortar.
- Cost-Effectiveness: Lime–cement mortar is more economical compared to pure cement mortar.
- Dense and Durable: Produces a dense mix suitable for load-bearing applications.
- Workability: Retains the plasticity and easy-to-apply characteristics of lime mortar.
Applications of Lime–Cement Mortar
- Bedding Mortar: Ideal for laying masonry units in applications requiring moderate strength.
- Thick Brick Walls: Provides stability and durability for thick brickwork, making it suitable for larger structures.
Lime–cement mortar is a versatile choice for projects requiring a balance between strength, workability, and cost. It is especially advantageous for applications where early strength and long-term durability are essential.
5. Mud Mortar
Mud mortar is a traditional type of mortar made by puddling or pugging cohesive clay with water until the desired consistency is achieved. To reduce shrinkage and minimize the occurrence of cracks during drying, fibrous materials such as straw, jute, or animal hair are often added. Thorough mixing of all ingredients is crucial for achieving a uniform and durable composition.
Characteristics of Mud Mortar
- Preparation: Requires proper kneading of cohesive clay with water, and optionally, the addition of weather-resistant agents like bitumen.
- Durability: The life of mud mortar typically ranges from 5 to 15 years, depending on the effectiveness of its water-proofing treatment and the local weather conditions.
Applications of Mud Mortar
Mud mortar has been in use since ancient times and is still prevalent in rural and economically sustainable construction. Its uses include:
- Brickwork for Ordinary Buildings: Often used in low-cost construction for small structures.
- Surface Floors: Provides a durable, smooth surface for basic flooring applications.
- Plastering Walls: Applied to internal walls and occasionally on external walls with protective treatments.
Weather-Proofing Measures of Mud Mortar
To enhance its weather resistance:
- Surface Coating: Mud-plastered surfaces can be sprayed or painted with bituminous materials for rain protection.
- Integrated Treatment: Bituminous materials can also be mixed into the mortar during preparation, improving its weather-proofing properties.
Mud mortar is a sustainable and cost-effective material, particularly suitable for rural areas or projects aiming to minimize environmental impact. With proper treatment and maintenance, it can serve as a reliable option for various construction needs, reflecting a balance of tradition and practicality.
Other Types of Mortar
In addition to the commonly used types of mortar discussed earlier, several specialized mortars are tailored for specific purposes. These include:
6. Fire-Resistant Mortar
Fire-resistant mortar is prepared by mixing aluminous cement with finely ground powder of fire bricks. This type of mortar is specifically designed to withstand high temperatures and is commonly used in furnace linings, fireplaces, and other heat-intensive structures.
7. Light-Weight Mortar
Light-weight mortar is created by adding materials such as sawdust, wood powder, asbestos fibers, or jute fibers to lime or cement mortar. This type of mortar is ideal for sound-proof and heat-proof construction, making it suitable for insulation purposes.
8. Packing Mortar
Packing mortar is a specialized mortar known for its high homogeneity, water resistance, and predetermined setting time. It forms solid, water-proof plugs and is widely used for plugging cracks or voids in rocks, resisting subsoil water pressure, and sealing oil wells. Variations include cement-sand, cement-loam, and cement-sand-loam mortars.
9. Sound-Absorbing Mortar
This mortar is a mix of Portland cement, lime, gypsum, and slag, combined with light-weight, porous aggregates such as pumice and cinders. It is used for acoustic insulation, reducing sound transmission in buildings.
10. X-Ray Shielding Mortar
X-ray shielding mortar is a dense, heavy mortar made from crushed heavy rocks and specific admixtures to block radiation. A plastering coat of this mortar is applied to the walls and ceilings of X-ray rooms, providing effective radiation shielding.
Types of Mortar Based on Bulk Density
Mortar can also be classified based on its bulk density, which is a measure of the mass of the mortar per unit volume. The bulk density influences the mortar’s weight, strength, and insulation properties. Mortars are generally categorized into two types based on their bulk density:
1. Heavyweight Mortar
- Bulk Density: Greater than 1500 kg/m³
- Aggregate: Typically made with heavy aggregates like heavy quartz or sand.
- Characteristics: These mortars are dense, offering greater strength and durability, making them ideal for structural applications where load-bearing capacity is critical.
2. Lightweight Mortar
- Bulk Density: Less than 1500 kg/m³
- Aggregate: Made with light, porous aggregates such as pumice, tuff, slag, or similar materials.
- Characteristics: Lightweight mortars have lower strength compared to heavyweight types but offer excellent thermal insulation, sound absorption, and ease of handling. They are ideal for non-load-bearing applications, acoustic treatments, and insulation.
Frequently Asked Questions
Common types of mortar include lime mortar, cement mortar, surkhi mortar, lime–cement mortar, and mud mortar. Specialized mortars such as fire-resistant, sound-absorbing, and X-ray shielding mortars are also used for specific applications.
Factors include the structural requirements, environmental conditions, load-bearing needs, and the desired properties such as water resistance, durability, or workability.
Lime mortar is often preferred for repointing bricks, especially in historic restoration projects, due to its workability, compatibility with older materials, and reduced shrinkage.
Cement mortar, specifically a mix with a lower sand ratio, is commonly used for shower pans due to its water resistance and durability.
