Mortar in Brickwork Construction
Brickwork construction requires careful consideration of various factors, including the type of mortar used. Mortar acts as the binding agent between bricks, providing strength and stability to the overall structure.
In this article, we will explore some important points to remember when working with mortar in brickwork construction.
1. Strength of Brickwork:
It is essential to understand that the strength of brickwork primarily depends on the strength of the bricks themselves, rather than the grade of the mortar used. Mortar mixes with different grades, such as M1 and M2, may have different strengths, but they do not significantly impact the overall strength of the brickwork. For instance, mortar mixes with ratios of 1:6 and 1:4 can result in the same strength of brickwork when using the same type of bricks.
2. Dense Mortar:
A mortar mix ratio of 1:3, whether it is cement to sand or a combination of cement and lime to sand, provides a dense mortar with fewer voids. This density contributes to the overall durability and stability of the brickwork.
3. Advantages of Lime Mortar:
Lime mortar, despite having lower strength compared to cement mortar, offers several advantages that make it a popular choice in brickwork construction:
a. Reduced Shrinkage:
Lime mortar experiences less shrinkage, making it less prone to cracks caused by shrinkage.
b. Improved Workability:
Lime increases the workability and plasticity of mortar, making it easier to handle during construction.
c. Water Retention:
Lime has excellent water retention capacity, which prevents rapid evaporation and ensures that dry bricks do not absorb water from the mortar quickly.
d. Enhanced Bonding:
Lime mortar exhibits better bonding with bricks, promoting structural integrity.
Cement-lime mortar is more flexible and can accommodate normal movements of brick masonry without cracking, making it less susceptible to damage.
f. Water Resistance:
Lime mortar increases the volume of the mortar and fills voids, making it more resistant to water penetration and enhancing overall water tightness.
4. Lime Mortar Strength:
Lime mortar gains strength slowly and generally has lower ultimate strength compared to cement mortar. However, lime mortar that incorporates hydraulic lime can achieve better and earlier strength. Fat lime mortars do not harden in wet locations, but the addition of pozzolanic materials, such as burnt clay instead of sand, can improve their strength.
5. Workability of Cement-Lime Mortar:
Leaner mixes of cement-lime mortar, ranging from ratios of 1:4 to 1:8, tend to be harsh, particularly if the sand used is coarse and not graded. In such cases, plasticizers are recommended to improve the workability and plasticity of the mortar, making it easier to handle and apply.
6. Factors Affecting Cement Mortar Strength:
Several factors can influence the strength of cement mortar, even when using the same cement-to-sand ratio:
a. Grading of Sand:
The particle size distribution of sand affects mortar strength.
b. Fineness and Coarseness of Sand:
The fineness and coarseness of sand particles impact mortar strength and plasticity.
c. Angularity and Roundness:
The shape of sand particles, whether angular or rounded, also plays a role in determining mortar strength.
Adjusting the quantity of cement can increase the plasticity of the mortar, but this approach may result in higher costs.
7. Fineness of Sand and Workability:
Increasing the fineness of sand improves the workability of cement-mortar mixtures. However, it also increases the surface area of the sand, requiring more cement and water to achieve the desired strength. If the cement quantity is not increased proportionally, the water-cement ratio rises, potentially reducing the overall strength of the mortar.
8. Importance of Curing:
Proper curing is crucial to achieve maximum strength and ensure the optimal coating of cement around sand particles. Adequate curing helps the mortar reach its full potential and enhances the durability of the brickwork.
9. Optimal Mortar Ratio:
Mortar richer than a mix ratio of 1:3 should be avoided in brickwork masonry construction due to high shrinkage and minimal gain in masonry strength. However, weak mortar is advantageous when considering factors like reduced cracking and accommodating movements caused by expansion and contraction. To overcome the limitations of lean mortar, composite mortar with a blend of cement, lime, and sand is preferable.
10. Lime-Based Mortars:
Lime-based mortars, such as cement-lime mortar or lime mortar, can provide higher strength for brickwork compared to pure cement mortar. For example, a cement-sand ratio of 1:6 may result in a mortar strength of 30 kg/cm2 but have a brickwork strength of 5.5 kg/cm2. In contrast, a cement-lime and sand mix ratio of 1:1:6, with the same mortar strength of 30 kg/cm2, can achieve a higher brickwork strength of 7 kg/cm2.
11. Common Defects in Mortar:
During brickwork construction, several defects can occur in the mortar, including:
a. Improper Mixing:
Inadequate mixing can lead to inconsistent mortar composition and compromised strength.
b. Excessive Water Content:
Adding too much water to the mortar weakens its strength and can cause issues during application.
c. Unduly Thick Bed:
Applying mortar beds that are excessively thick can reduce the strength of the brickwork.
d. High Suction of Bricks:
Bricks with high suction and mortar with low water retentivity can result in improper bonding.
e. Uneven Joints:
Inconsistent joint thickness can affect the overall appearance and integrity of the brickwork.
f. Voids in Vertical Joints:
Failure to properly fill vertical joints can create weak points in the structure.
g. Disturbance of Bricks:
Mishandling or disturbing freshly laid bricks can lead to misalignment and compromised structural integrity.
Impact of Joint Thickness:
Overly thick joints in brickwork can weaken the overall strength of the structure. It is important to maintain consistent and appropriate joint thickness to ensure structural stability.
Incorporating pozzolanic materials in the mortar mixture increases its strength and resistance to chemical attacks. This can be beneficial in environments where the mortar may be exposed to harsh conditions.
By considering these points and implementing best practices for mortar usage in brickwork construction, builders can ensure the longevity, strength, and stability of the structures they construct.