The common types of mortar mix are designated by the letters M, S, N, O, and K, each representing different compressive strengths.
Mortar Mix Types:
These designations, introduced in 1954, replaced the earlier A-1, A-2, B, and C classifications. The letter progression comes from the term "MASON WORK", using every other letter in descending order of strength. Here's a breakdown:
| Mortar Type | Description | Compressive Strength (psi) | Usage Examples |
|---|---|---|---|
| Type M | The strongest mix with the highest compressive strength | 2500 | Heavy loads, reinforced masonry, below-grade applications. |
| Type S | High strength, suitable for more demanding structural applications | 1800 | Below-grade walls, retaining walls, structural masonry. |
| Type N | Medium strength, most commonly used general-purpose mortar mix. | 750 | Above-grade walls, general brickwork. |
| Type O | Lower strength, often used for interior, non-load-bearing applications. | 350 | Interior applications, non-load-bearing walls, and historical projects. |
| Type K | The weakest mix with the lowest compressive strength, rarely used in construction. | 75 | Restoring old masonry, very weak masonry, and historic buildings. |
Key Insights:
- The strength of the mortar decreases from type M to K.
- The letter designations were based on the term "MASON WORK" using every other letter, each in a descending order of strength.
- Each type is designed for specific applications, depending on the structural needs.
- Choosing the correct type of mortar mix is crucial to ensure the longevity and integrity of a masonry structure.
Practical Considerations:
- Type M: Used where high compressive strength is necessary, such as below-grade foundations and load-bearing walls.
- Type S: A good choice for projects requiring moderate to high strength and good bonding, such as retaining walls.
- Type N: Versatile and commonly used for above-grade brick and blockwork where moderate strength is required.
- Type O: Ideal for interior, non-structural applications where lower strength is acceptable, and for historic masonry.
- Type K: Rarely used in modern construction and primarily used for specific historic restoration projects.
