Which mortar type must be used in multi-unit masonry construction?

In multi-unit masonry construction, the use of Type S mortar is essential due to its strength and flexibility. Type S mortar has a compressive strength of at least 1,800 psi and excellent bonding characteristics, making it suitable for use in applications subject to lateral pressures, such as high-rise buildings and structures with multiple units.

The specific properties of Type S mortar allow it to withstand greater loads and provide enhanced resilience against wind and seismic forces, which are common considerations in multi-unit structures. This type of mortar also offers sufficient water resistance and durability for exterior walls, where performance against weathering is critical.

While other mortar types such as Type N, Type M, and Type O have distinct characteristics and appropriate applications, they do not align with the structural and environmental demands of multi-unit masonry construction as effectively as Type S. For instance, Type N is often used for above-grade interior and exterior masonry but lacks the compressive strength required for heavy loads. Type M is stronger but is typically used in specific applications like below-grade work. Type O has a low compressive strength and is generally suited for non-load bearing walls. Therefore, Type S is the most appropriate choice for ensuring the structural integrity and longevity of multi-unit masonry projects.