Considerations for Mortar in Brickwork Construction
In brickwork construction, various mortar grades such as M1, M2, and so on are used. Lime mortar and cement mortar are two common types of mortar used in bricklaying. The properties, strength, and applications of these mortars under various conditions should be understood.
Considerations for Mortar in Brickwork Construction
1. The strength of brickwork is unaffected by the grade of mortar used, i.e. different mortar mixes of different grades, such as M1 and M2, have different strengths, but this has no bearing on the strength of brickwork. For example, mortars with mix ratios of 1:6 and 1:4 provide the same strength of brickwork with the same type of bricks, despite their differences in strength. That is, the strength of brickwork is determined by the strength of the bricks.
2. A mortar mix ratio of 1:3 for cement to sand or (cement + lime) to sand results in a dense mortar with fewer voids.
3. Benefits of Lime Mortar - Despite the fact that lime mortar has a lower strength than cement mortar, the benefits of including lime in mortar are as follows:
- Because shrinkage is less in mortar, it is less prone to cracking.
- The addition of lime to the mortar mix improves its workability and plasticity.
- Lime has a high capacity for water retention and does not evaporate quickly. Furthermore, dry bricks cannot absorb water from lime mortar.
- Lime expands the volume of the mortar and fills voids, making it water resistant. As a result, lime mortar provides greater water tightness and resistance to rain penetration.
- Lime mortar bonds better with bricks.
- Cement-lime mortar is more malleable and can withstand normal masonry movement without cracking. As a result, cement lime mortar is less prone to cracking than cement mortar.
4. Lime mortar has a lower ultimate strength than cement mortar and gains strength slowly. Again, lime mortar containing hydraulic lime achieves greater and earlier strength. In wet conditions, lime mortar made with fat lime does not harden at all.
Semi-hydraulic lime mortars have properties that are halfway between hydraulic and fat lime mortars. To improve mortar strength when using fat lime, some pozzolanic materials such as burnt clay must be used in place of sand.
5. Cement-lime mortar in leaner ratios of 1:4 to 1:8 tends to be harsh, especially if the sand is coarse and not graded. As a result, plasticizers are suggested for use in order to improve the workability and plasticity of the mortar.
Mortar in Brickwork Construction
6. The following factors influence the strength of cement mortar when the cement and sand ratios are the same:
- Sand grading
- Sand coarseness and fineness
- The angularity and roundness of the sand particles
For the same cement/sand ratio, the plasticity of the cement mortar mix varies with the fineness of the sand. The plasticity of cement mortar can be increased by increasing the amount of cement used, but this increases the cost of the mortar.
The amount of water to be added should be just enough to give the mix enough workability, which should also vary depending on the above three factors. If the above three factors result in the use of less water, the strength of the mortar will be greater.
7. As sand fineness increases, so does the workability of the cement-mortar mix, but it also increases the surface area of the sand, requiring more cement and water for the same strength. Strength will be reduced if the cement quantity is not increased. To achieve the desired workability, more water will be required. This condition lowers the strength by increasing the water-cement ratio.
8. Curing is essential for achieving maximum strength and maximising the coating of available cement around sand particles.
9. Mortar richer than a 1:3 mix ratio is not used in brickwork masonry construction due to high shrinkage and no discernible gain in masonry strength, even though the strength of the mortar itself increases.
Cracks will be fewer and wider if strong mortar is used, whereas cracking will be distributed as thin hair cracks if weak mortar is used. Weak mortar reduces stresses caused by differential movement of masonry due to expansion, contraction, and so on, because weak mortar can easily accommodate the movements.
As a result, when strong mortar is not required due to strength, weak mortar should be used. Because lean mortar of just cement and sand is harsh, pervious, less workable, and less plastic, composite mortar of cement, lime, and sand is preferred.
10. Lime-based mortars, such as cement-lime mortar or lime mortar, provide greater brickwork strength for the same mortar strength as cement mortar.
For example, a cement-sand ratio of 1:6 results in mortar strength of 30 kg/cm2 and brickwork strength of 5.5 kg/cm2, whereas a cement-lime and sand-mix ratio of 1:1:6 results in mortar strength of 30 kg/cm2 and brickwork strength of 7 kg/cm2.
11. The following are the most common mortar defects discovered during brickwork construction:
- Incorrect mixing
- Excessive moisture content
- An excessively thick bed
- High brick suction and low mortar water retentivity
- Uneven joint surfaces
- Vertical joint voids
- Brick movement immediately after laying
12. Excessively thick joints weaken the brickwork.
13. Adding pozzolana to the mortar increases its strength and resistance to chemical attacks.
- Because shrinkage is less in mortar, it is less prone to cracking.
- The addition of lime to the mortar mix improves its workability and plasticity.
- Lime has a high capacity for water retention and does not evaporate quickly. Furthermore, dry bricks cannot absorb water from lime mortar.
- Lime expands the volume of the mortar and fills voids, making it water resistant. As a result, lime mortar provides greater water tightness and resistance to rain penetration.
- Lime mortar bonds better with bricks.
- Cement-lime mortar is more malleable and can withstand normal masonry movement without cracking. As a result, cement lime mortar is less prone to cracking than cement mortar.
4. Lime mortar has a lower ultimate strength than cement mortar and gains strength slowly. Again, lime mortar containing hydraulic lime achieves greater and earlier strength. In wet conditions, lime mortar made with fat lime does not harden at all.
Semi-hydraulic lime mortars have properties that are halfway between hydraulic and fat lime mortars. To improve mortar strength when using fat lime, some pozzolanic materials such as burnt clay must be used in place of sand.
5. Cement-lime mortar in leaner ratios of 1:4 to 1:8 tends to be harsh, especially if the sand is coarse and not graded. As a result, plasticizers are suggested for use in order to improve the workability and plasticity of the mortar.
Mortar in Brickwork Construction
6. The following factors influence the strength of cement mortar when the cement and sand ratios are the same:
- Sand grading
- Sand coarseness and fineness
- The angularity and roundness of the sand particles
For the same cement/sand ratio, the plasticity of the cement mortar mix varies with the fineness of the sand. The plasticity of cement mortar can be increased by increasing the amount of cement used, but this increases the cost of the mortar.
The amount of water to be added should be just enough to give the mix enough workability, which should also vary depending on the above three factors. If the above three factors result in the use of less water, the strength of the mortar will be greater.
7. As sand fineness increases, so does the workability of the cement-mortar mix, but it also increases the surface area of the sand, requiring more cement and water for the same strength. Strength will be reduced if the cement quantity is not increased. To achieve the desired workability, more water will be required. This condition lowers the strength by increasing the water-cement ratio.
8. Curing is essential for achieving maximum strength and maximising the coating of available cement around sand particles.
9. Mortar richer than a 1:3 mix ratio is not used in brickwork masonry construction due to high shrinkage and no discernible gain in masonry strength, even though the strength of the mortar itself increases.
Cracks will be fewer and wider if strong mortar is used, whereas cracking will be distributed as thin hair cracks if weak mortar is used. Weak mortar reduces stresses caused by differential movement of masonry due to expansion, contraction, and so on, because weak mortar can easily accommodate the movements.
As a result, when strong mortar is not required due to strength, weak mortar should be used. Because lean mortar of just cement and sand is harsh, pervious, less workable, and less plastic, composite mortar of cement, lime, and sand is preferred.
10. Lime-based mortars, such as cement-lime mortar or lime mortar, provide greater brickwork strength for the same mortar strength as cement mortar.
For example, a cement-sand ratio of 1:6 results in mortar strength of 30 kg/cm2 and brickwork strength of 5.5 kg/cm2, whereas a cement-lime and sand-mix ratio of 1:1:6 results in mortar strength of 30 kg/cm2 and brickwork strength of 7 kg/cm2.
11. The following are the most common mortar defects discovered during brickwork construction:
- Incorrect mixing
- Excessive moisture content
- An excessively thick bed
- High brick suction and low mortar water retentivity
- Uneven joint surfaces
- Vertical joint voids
- Brick movement immediately after laying
12. Excessively thick joints weaken the brickwork.
13. Adding pozzolana to the mortar increases its strength and resistance to chemical attacks.
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