During the rainy season in Hawaii, a contractor notices moisture intrusion through a concrete masonry unit (CMU) wall. What is the most likely cause and solution?
Correct Answer
C) Incomplete mortar joints; repoint and seal
Incomplete mortar joints in CMU construction create pathways for water penetration. Repointing with proper mortar and applying masonry sealer addresses the primary moisture entry points.
Why This Is the Correct Answer
Incomplete or poorly filled mortar joints are the most common cause of moisture intrusion in CMU construction. Hawaii's heavy tropical rainfall creates sustained hydrostatic pressure against walls, and any voids or hairline cracks in mortar joints become direct water pathways. Repointing (tuckpointing) with fresh mortar and then applying a breathable masonry sealer eliminates these entry points.
Why the Other Options Are Wrong
Option A: Missing dampproofing; install vapor barrier
Dampproofing and vapor barriers address moisture migration through the wall mass (diffusion) and foundation contact, not through joint voids. Installing a vapor barrier does not seal the surface mortar joints where rain is actively entering.
Option B: Thermal movement; install expansion joints
Thermal movement and expansion joints address cracking from temperature-induced expansion/contraction — a concern in mainland climates with large temperature swings. Hawaii's relatively stable tropical temperatures make this an unlikely primary cause of sudden rainy-season intrusion.
Option D: Inadequate curing; apply surface sealer
Inadequate curing affects the compressive strength and shrinkage of concrete elements but does not directly cause the mortar joint voids that allow water infiltration. A surface sealer alone without repointing would not address voids in the joints.
Memory Technique
CMU wall + rain + Hawaii = think 'joint failure.' Mortar joints are the weakest point in a CMU wall — they're the first to crack, shrink, or be poorly filled. Rain + joints = repoint and seal. Rhyme: 'When rain comes in, check the joints — repoint and seal, that's the point.'
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