North Carolina Building Contractor License Practice Exam

Which type of mortar is generally used for structures that are below grade?

1. Type O

2. Type N

3. Type S

4. Type M

The correct answer is: Type M

Type M mortar is designed for use in structures that are below grade due to its high compressive strength and low water absorption characteristics. This type of mortar is particularly suitable for construction applications such as foundations, below-grade walls, and retaining walls, where the structural integrity and resistance to moisture are critical. The high compressive strength of Type M mortar (around 2,500 psi or greater) makes it ideal for load-bearing applications in environments where moisture can be a concern. It is made with a stronger cement-to-lime ratio compared to the other types, ensuring durability in harsh conditions often encountered in below-grade situations. Additionally, the low water absorption aligns well with the need to prevent water infiltration in structures that face direct contact with soil and groundwater. This quality helps in protecting the integrity of the building while minimizing the risk of deterioration caused by moisture-related issues.