What type of mortar is typically specified for load-bearing masonry walls below grade?
Correct Answer
D) Type S mortar
Type S mortar has high tensile bond strength and is recommended for below-grade masonry, load-bearing walls, and areas subject to high lateral loads. It provides better resistance to moisture and freeze-thaw cycles than Type N.
Why This Is the Correct Answer
Type S mortar is specifically designed for high-strength applications and provides superior tensile bond strength compared to other mortar types. Its composition makes it highly resistant to moisture penetration and freeze-thaw cycles, which are critical factors for below-grade applications. The high strength characteristics of Type S mortar make it ideal for load-bearing walls that must support structural loads while being exposed to ground moisture and potential frost conditions. This mortar type maintains its integrity and bond strength even under the harsh conditions typically found in below-grade masonry applications.
Why the Other Options Are Wrong
Option B: Type O mortar
Type N mortar is a general-purpose mortar with medium strength that is typically used for above-grade applications like exterior walls and chimneys. While it has good workability, it lacks the high tensile bond strength and moisture resistance required for below-grade load-bearing applications.
Option C: Type K mortar
Type O mortar is a low-strength mortar primarily used for interior non-load-bearing applications and repointing work. It has insufficient strength and poor moisture resistance, making it completely unsuitable for below-grade load-bearing walls that require high performance characteristics.
Memory Technique
Use the mnemonic 'My Strong Nephew Only Kicks' for mortar types M-S-N-O-K in descending strength order. Remember 'S is for Strong Structures below grade' - Type S mortar for structural applications below ground level.
Reference Hint
Florida Building Code, Chapter 21 - Masonry, or ACI 530/ASCE 5/TMS 402 Building Code Requirements for Masonry Structures, Section on mortar specifications and applications
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