Which mortar type is typically specified for above-grade masonry in seismic areas for higher bond and flexibility?

• A. Type N mortar
• B. Type M mortar
• C. Type S mortar
• D. Type O mortar

Answer: (C)

In seismic areas, masonry walls need to resist lateral movement and accommodate some shifting without losing bond. Mortar designed for higher bond strength and a bit more flexibility helps the masonry stay intact under seismic loads. Structural mortar, Type S, is formulated to provide this higher bond strength and improved performance compared with other common mortars, making it the typical choice for above-grade masonry in earthquakes. Type M is very strong in compression but tends to be stiff and less forgiving of movement; Type N is a general-purpose mortar with lower bond strength, and Type O is a low-strength mix used mainly for non-load-bearing interior work.