Bulging Brick Wall Between RCC Columns
At a PSEB NSQF construction practical site, a 230 mm thick brick wall 3.0 m high and 6.0 m long is being built between two RCC columns. The mason uses a 1:6 cement–sand mortar mixed by volume, but the helper measures sand with woven baskets of uncertain capacity and adds water until the mortar 'looks easy to spread'. Bricks are taken straight from a stack in full sun at 38 °C and laid without wetting. The wall rises about 1.4 m in one day. The mason checks plumb only when the wall reaches full height. Next morning the top 1.5 m shows an 18 mm outward bulge, wide bed joints near the bulge, and a vertical crack at the junction with one column. The client wants handover in four days. The site supervisor must decide whether to plaster over the area or rebuild it.
1. What are the most probable causes of the bulge and crack? Link each cause to the observed symptom rather than listing general defects.
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The bulge is not caused by one factor. Dry bricks at 38 °C absorb water from the mortar, so the bed joint stiffens before the brick is aligned; this gives thick, poorly bonded joints and allows the upper courses to move outward. Basket batching makes the cement content variable, so some batches are lean and slow-setting; a lean mortar cannot resist the lateral thrust of 1.4 m of fresh masonry in one day. Raising the wall too fast means the lower mortar is still green when the top is built, so the wall compacts and bulges. Checking plumb only at the end lets error accumulate without correction. The vertical crack at the column junction points to a weak connection: the wall was probably not toothed or tied into the column, so the two elements moved differently.
2. Should the supervisor plaster over the wall? Give a decision and a safe correction sequence.
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No. Plastering would hide a structural defect, add load, and the crack would telegraph through. An 18 mm bulge is far beyond normal masonry tolerance and cannot be corrected by a thick plaster coat. Rebuild the affected length. Sequence: (1) isolate and prop the wall if the top is connected to the slab or beam; (2) remove masonry from at least 500 mm below the visible bulge, cutting out cracked units; (3) clean and wet the bricks; (4) remake mortar with a gauge box, 1:6 by volume, and use it within 30–45 minutes; (5) rebuild in lifts not exceeding 1 m per day, checking plumb and level every three or four courses; (6) form a proper toothed or tied junction with the column; (7) cure the new masonry and have the engineer inspect before plaster.
3. What controls would prevent recurrence in the next wall?
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Use a standard measuring box, not baskets; keep sand dry and measure volume consistently. Wet bricks before laying, but do not leave them dripping. Build in lifts of about 1 m and let mortar set before loading. Check plumb with a spirit level and plumb rule at every course, not only at the top. Provide toothing or approved ties at column junctions. Use a line and corner blocks; check diagonals of wall panels. Cure masonry for at least 7 days. Record mortar batch proportions and brick absorption. These controls address the observed causes rather than just telling the mason to be careful.