Masonry construction is a fundamental aspect of building, relying on various materials to create strong, durable structures. One of the most critical components of masonry is mortar, a workable paste produced by mixing water with a combination of binding material and fine aggregate. This plastic paste plays a crucial role in binding materials like stone and brick together. In this article, we will explore the different types of mortars used in masonry construction, categorized by application, binding material, bulk density, strength, and special purposes.
Based on Applications
Bricklaying or Stone Laying Mortar
Bricklaying or stone laying mortar is primarily used to bind bricks and stones in masonry construction. The proportions of the ingredients for this type of mortar depend on the kind of binding material used. Properly formulated, this mortar provides the strength necessary for the structural integrity of the building.
Finishing Mortar
Finishing mortar is employed for pointing, plastering, and creating architectural effects. Its aesthetic properties are essential for giving buildings an appealing appearance. This type of mortar must possess high strength, mobility, and resistance to atmospheric conditions, such as rain and wind, ensuring durability over time.
Based on Binding Material
Cement Mortar
Cement mortar utilizes cement as the binding material, with sand serving as the aggregate. The proportions of cement and sand are determined based on specified durability and working conditions. This type of mortar is renowned for its high strength and resistance to water, with typical ratios ranging from 1:2 to 1:6.
Lime Mortar
Lime mortar incorporates lime as the binding material and can be classified into two types: fat lime and hydraulic lime. Fat lime requires 2 to 3 times the amount of sand and is suitable for dry work, while hydraulic lime is used in damp conditions, often in a 1:2 ratio with sand. Lime mortar is characterized by its high plasticity, making it easy to work with, and has been used in historical structures like the pyramids at Giza.
Gypsum Mortar
Gypsum mortar consists of plaster and soft sand. While it is relatively easy to work with, it has low durability in damp conditions, making it less suitable for areas exposed to moisture.
Gauged Mortar
Gauged mortar combines lime and cement, using sand as fine aggregate. This blend enhances the strength of traditional lime mortar by incorporating cement, resulting in a mixture that retains the plasticity of lime while gaining the strength of cement. The typical cement-to-lime ratio ranges from 1:6 to 1:9, making it a cost-effective choice for various applications.
Surkhi Mortar
Surkhi mortar uses lime as the binding material and surkhi, a finely powdered burnt clay, as the fine aggregate. This combination provides greater strength than traditional sand and is often more cost-effective.
Aerated Cement Mortar
Aerated cement mortar is a type of cement mortar to which an air-entraining agent is added. This modification increases the mortar’s plasticity and workability, making it easier to apply in various construction scenarios.
Mud Mortar
Mud mortar is composed of mud as the binding material, with aggregates like sawdust, rice husk, or cow dung. This type of mortar is commonly used in regions where lime or cement is not readily available, and its historical use is well documented in Middle-Eastern and Southwestern U.S. architecture.
Based on Bulk Density
Heavy Mortar
Heavy mortar is characterized by a bulk density of 15 KN/m³ or more. It typically incorporates heavy quartzes as fine aggregate, making it suitable for applications requiring additional weight and stability.
Lightweight Mortar
In contrast, lightweight mortar has a bulk density of less than 15 KN/m³. It is created by mixing lime or cement as a binder with aggregates such as sawdust, rice husk, jute fibers, coirs, or asbestos fibers. This type of mortar is often used in soundproofing and heat-proofing constructions, contributing to improved energy efficiency.
Based on Strength (ASTM C270)
Type M Mortar
Type M mortar is the highest strength mortar, with a minimum compressive strength of 17.2 MPa (2500 psi). It is ideal for exterior masonry and below-grade applications where significant gravity or lateral loads are present, such as load-bearing walls and footings.
Type S Mortar
Type S mortar is a medium-strength mortar with a minimum compressive strength of 12.4 MPa (1800 psi). It offers excellent bonding ability and durability, making it suitable for applications where masonry is in contact with the ground, like paving or shallow retaining walls.
Type N Mortar
Type N mortar is another medium-strength option, with a minimum strength of 5.2 MPa (750 psi). It is the most commonly used mortar type, ideal for reinforced interior and above-grade exterior load-bearing walls.
Type O Mortar
Type O mortar is classified as low strength, with a minimum strength of 2.5 MPa (350 psi). It is primarily used for interior non-load-bearing applications and repointing, where the structural integrity of the wall is intact.
Based on Special Purpose of Mortars
Fire-Resistant Mortar
Fire-resistant mortar is specially formulated by mixing aluminous cement with fine powder from fire bricks. This type of mortar is critical in structures at risk of fire, providing an effective fireproof barrier.
Packing Mortar
Packing mortar typically consists of a mixture of cement-sand, cement-loam, or cement-sand-loam. It is designed for applications requiring high homogeneity and water resistance, such as in oil wells.
Sound Absorbing Mortar
Sound absorbing mortar combines binding materials like cement, lime, gypsum, or slag with aggregates such as pumice or cinders. It effectively reduces noise levels, acting as a soundproof layer in construction.
X-ray Shielding Mortar
X-ray shielding mortar provides protection against harmful X-rays and is used to plaster the walls and ceilings of X-ray rooms. It is characterized by a high bulk density of around 22 KN/m³, incorporating heavy rock aggregates and suitable admixtures.
Chemical Resistant Mortar
Chemical-resistant mortar is essential in environments susceptible to chemical attacks. The formulation varies based on the anticipated exposure to specific chemicals, with certain types, like silicate-based mortars, providing resistance to acidic damage but not to alkalis.
Conclusion
Understanding the various types of mortars used in masonry construction is crucial for selecting the right material for specific applications. Each type of mortar, whether based on application, binding material, bulk density, strength, or special purpose, offers unique benefits suited to different construction needs. Proper selection ensures structural integrity, durability, and aesthetic appeal, contributing to the longevity and performance of masonry structures.