What type of mortar is typically used for below-grade masonry construction?
Correct Answer
D) Type S
Type S mortar has high tensile bond strength and is recommended for below-grade masonry, masonry subjected to high lateral loads, and areas requiring high flexural bond strength. It provides better resistance to moisture and freeze-thaw cycles.
Why This Is the Correct Answer
Type S mortar is specifically designed for below-grade masonry construction due to its high tensile bond strength and superior resistance to moisture penetration. It contains higher cement content than Types N and O, providing excellent durability against freeze-thaw cycles and hydrostatic pressure commonly encountered in foundation walls, basement construction, and other below-grade applications where structural integrity and moisture resistance are critical.
Why the Other Options Are Wrong
Option A: Type N
Type N mortar is a general-purpose mortar with medium strength, primarily used for above-grade exterior walls and interior load-bearing walls. While versatile, it lacks the high tensile bond strength and moisture resistance required for below-grade applications where hydrostatic pressure and freeze-thaw cycles are concerns.
Option B: Type O
Type O mortar has the lowest compressive strength among common mortar types and is typically used for non-load-bearing interior applications and repointing historic masonry. Its low strength and poor moisture resistance make it unsuitable for the demanding conditions of below-grade construction.
Option C: Type M
Type M mortar has the highest compressive strength but relatively low tensile bond strength and poor workability. While strong, it's typically used for heavy structural loads above grade, severe weather exposure, and below-grade applications in contact with earth, but Type S is preferred for most below-grade masonry due to better bond strength.
Memory Technique
Remember 'S for Subterranean' - Type S mortar goes below grade because it has Superior bond Strength and moisture resistance for Structural applications underground.
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