Final answer:
Type O mortar is known for its low compressive strength and is typically used for interior non-load-bearing walls, making it ideal for projects that require a mortar with good bonding and workability but not high strength.
Step-by-step explanation:
The type of mortar that has a low compressive strength and is usually used for interior walls is Type O mortar. Mortar is a mix of binding material with sand and water, and its composition determines its strength, flexibility, and other properties. In the realm of mortar types, there are different classifications, each suited for specific types of work and environmental conditions.
Type N mortar is a general-purpose mortar with moderate strength, making it suitable for both above-grade, exterior, and interior load-bearing installations. Type S mortar has high tensile strength, which makes it suitable for areas where the ground may shift or for structures that might endure heavy loads or high winds. Type M mortar has the highest strength and is used in the construction of foundations, retaining walls, and other structures where high compressive strength is required.
Type O mortar, on the other hand, is designed for non-load-bearing applications where a lower strength is sufficient. This makes it ideal for interior walls that do not support any significant weight. Its low strength is also beneficial for projects where the respective structure requires a mortar with good bonding properties that needs to be easy to handle, as Type O's flexibility can accommodate slight movements within a building without causing damage.
For example, when restoring historic buildings where the use of a soft mortar is necessary to prevent damage to the existing masonry units, or in the case of decorative internal stonework where maximum strength is not required. Moreover, Type O mortar's good workability makes it a preferred choice for repointing and similar delicate masonry work.