Building with a sand/cement mortar & pointing with lime mortar

September 4th 2016 in Design
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Introduction

Building a wall with a sand and cement mortar and then pointing it with a lime mortar can have several disadvantages, primarily because these two types of mortars have different properties and characteristics. 

Here are some of the disadvantages of such a construction approach:

Incompatibility: Sand and cement mortar and lime mortar have different properties and curing times. Lime mortar is more flexible and breathable, while cement mortar is rigid and less breathable. Mixing the two can result in compatibility issues, leading to cracking and poor adhesion. 

Differential Movement: As the wall expands and contracts due to temperature changes and settling, the differing properties of the mortars can lead to differential movement between the two layers. This can cause cracking and separation over time. 

Aesthetics: Lime mortar has a different color and texture compared to cement mortar. When you point with lime mortar over a cement-based wall, the visual contrast can be quite noticeable, which may not be aesthetically pleasing. 

Maintenance Challenges: Maintaining a wall with two different types of mortar can be more challenging. Repairs or re-pointing may require specialized materials and expertise, making it more costly and time-consuming. 

Durability: Lime mortar is more flexible and can accommodate some degree of movement without cracking. Cement-based mortar is less forgiving and may crack when subjected to movement, impacting the overall durability of the wall. 

Historic Preservation: When working on historic or heritage buildings, it is essential to use materials and techniques that are consistent with the original construction. Mixing lime and cement mortar may not meet preservation standards and guidelines. 

Cost: Using two different types of mortar can increase construction costs due to the need for separate materials and labor for both phases of construction. 

Environmental Considerations: Cement production is energy-intensive and releases a significant amount of carbon dioxide (CO2) into the atmosphere. Using lime mortar, which has a lower environmental impact, for the entire construction process might be a more sustainable choice. 

Conclusion

In summary, while it is possible to build a wall with a sand and cement mortar and then point it with lime mortar, there are several disadvantages, including compatibility issues, differential movement, aesthetic concerns, and increased maintenance complexity. 

It's essential to carefully consider these factors before deciding on this construction approach, especially for projects where long-term durability and visual aesthetics are critical.

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