Mortar

The highest-strength mortar (2,500 psi) is Type M mortar, which is only used where considerable compressive strength is needed. Type M mortar is generally used with stone, since it’s very strong and won’t fail before the stone does. This mortar is used for below-grade applications involving extreme pressure or lateral loads, such as foundations and retaining walls. Type M mortar is made using three parts Portland cement, one part hydrated lime, and 12 parts sand.

Like Type N mortar, type S is medium-strength (1,800 psi,) but it’s stronger than Type N and can be used for below-grade exterior walls and outdoor patios. It’s ideal for applications where the building materials come into contact with the ground, such as shallow retaining walls and paving stones. Type S mortar is made with two parts Portland cement, one part hydrated lime, and nine parts sand.

Type N mortar mix is a medium-strength mortar (750 psi) recommended for exterior and above-grade walls and interior load-bearing walls. Type N mortar withstands high heat, low temperatures, and severe weather and is considered to be a general-purpose mix. It’s the most commonly used mortar by homeowners for general applications, and it’s ideal for semi-soft stone since it’s more flexible than higher-strength mortar and will help prevent the stone from cracking. Type N mortar is made using one part Portland cement, one part lime, and six parts sand.

Type O mortar mix is low-strength (350 psi) mortar used in non-load-bearing interior projects. It’s often used to repair mortars and is generally used with sandstone and other materials with low compressive strength, since it’s very flexible. This mortar has very limited exterior use. Type O mortar is made using one part Portland cement, two parts hydrated lime, and nine parts sand.