NASCLA Accredited Commercial General ContractorMasonryMedium
A contractor is evaluating different types of mortar for a structural brick wall project. Which type of mortar, designated by ASTM C270, is generally recommended for use in structural masonry where high compressive strength and severe weather exposure are anticipated?
- AType S
- BType N
- CType O
- DType M
Show answer & explanationAnswer & explanation
Correct answer: D. Type M
According to ASTM C270, Type M mortar offers the highest compressive strength and is suitable for structural masonry, severe weather exposure, and below-grade applications where high strength is critical.
Why the other options are wrong
- A. Type S mortar has intermediate to high strength, good for at-grade or below-grade masonry and where lateral loads are expected.
- B. Type N mortar is a general-purpose mortar with medium strength, suitable for exposed, above-grade, non-load-bearing walls.
- C. Type O mortar has low compressive strength and is typically used for interior, non-load-bearing walls or historic restoration.
ASTM C270 Mortar Types
Classifications of masonry mortar based on compressive strength and composition, denoted as M, S, N, O, and K (though K is rarely used).
- M: Highest strength, severe exposure, structural.
- S: High strength, at/below grade, lateral loads.
- N: Medium strength, general purpose, above grade.
- O: Low strength, interior, non-load-bearing.
- Strength decreases from M to O.
Memory trick: My Strong Nasty Old Kook: M, S, N, O, K for strength.