Which mortar type is medium-strength and suitable for exposed masonry above grade?

The choice of mortar type B, which is Type N, is appropriate because it is formulated to provide a medium level of strength, typically around 750 psi. This makes it particularly suitable for exposed masonry applications above grade, such as in walls that experience regular weather exposure. Type N mortar also has good workability and flexibility, allowing it to perform well in various conditions, including areas subject to moderate weathering.

Type N is often used in above-grade masonry construction because it can resist the elements while providing adequate strength to support the structure. Its composition typically includes one part Portland cement, one part lime, and six parts sand, which contributes to its durability and adaptability.

Other types of mortar, such as M, S, and O, serve different purposes or have varying strength attributes. For instance, Type M is a high-strength mortar, suitable for below-grade applications or where high compressive strength is needed but is typically too strong for most above-grade work. Type S offers high strength and is used where additional strength is necessary but may also be over-specification for typical above-grade masonry. Type O is a low-strength mortar, generally used in non-load-bearing applications, making it unsuitable for exposed masonry that requires medium strength and durability.