For reinforced masonry below grade and in contact with earth, which type of mortar should be used?

The use of Type S mortar for reinforced masonry below grade and in contact with earth is advisable due to its specific properties that suit subterranean environments. Type S mortar has a higher compressive strength than Type N, making it more resilient to the pressures and potential stresses from soil and water encountered in below-grade applications.

Additionally, Type S mortar provides excellent adhesion and is more flexible, which is vital in scenarios where slight movements could occur due to soil expansion or settling. Its ability to withstand moisture also helps in preventing issues such as cracking or failure of the masonry structure.

In contrast, while Type N mortar is a general-purpose mortar, it is not designed for heavy structural loads or for environments where moisture and soil pressure are significant concerns. This makes Type N less suitable for reinforced masonry applications that are below grade, particularly when in direct contact with the earth.

Therefore, Type S mortar is the correct choice for providing the strength, flexibility, and moisture resistance necessary for reinforced masonry in these conditions.