What is Type N vs Type S mortar?
Type N and Type S are ASTM mortar classifications ranked by compressive strength, with N suited for general work and S for load-bearing walls requiring greater durability.
ASTM C270 establishes four standard mortar types (M, S, N, O) ranked by compressive strength and cement content. Type S and Type N represent the middle range of this scale and address different structural demands in masonry work.
Type S mortar achieves 1,800 pounds per square inch (psi) compressive strength and contains higher cement ratios, making it suitable for load-bearing walls, structural foundations, and applications where joints must resist bending stress. Contractors use Type S in projects requiring durability and lateral resistance, such as below-grade work or structures exposed to weather extremes.
Type N mortar reaches 750 psi compressive strength and offers more flexibility, allowing for movement and settling in masonry assemblies. This type works well for interior walls, above-grade construction, and soft historic brick where lower strength and workability matter. Its higher lime content improves flow and bonding without excessive rigidity.
Choosing between these types depends on wall position, brick condition, and structural loads. Load-bearing exterior walls typically call for Type S, while general-purpose walls benefit from Type N's flexibility and easier application. Historic preservation often demands Type N or even softer mortars to protect aged brick from damage. Connecticut contractors must match mortar type to local soil conditions and freeze-thaw cycles that characterize the region's climate.