Efflorescence and Cracking in New Brick Masonry
You are the site supervisor for a two-storey vocational training building in Nashik. The 230 mm external walls were raised in the first week of June using locally supplied table-moulded bricks and a 1:6 cement-sand mortar. The bricks were stacked on bare ground and watered two days before use. After a spell of dry heat followed by intermittent rain, white salt patches appear on the lower 1.2 m of the north wall, and several diagonal hairline cracks run from the corners of window openings. Mortar joints vary from 8 mm to 18 mm; some perpends are unfilled. The mason proposes washing the wall with acid and painting it with cement paint before plastering. The client wants occupancy before the monsoon and asks whether the wall can be accepted. You have a 2 m straightedge, a 25 mm mortar cube testing facility, and photographs of the brick stack.
1. Identify the likely causes of the salt patches and diagonal cracks, and separate material defects, workmanship defects, and issues that need structural review.
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Salt patches: The most likely source is soluble salts in the bricks, sand, or mixing water, mobilised by moisture from the ground and the pre-wetting, then deposited as the wall dries. Stacking bricks on bare ground increases sulphate and salt absorption. This is mainly a material and storage defect, although poor curing and dampness can worsen it.
Diagonal cracks at opening corners: These are classic stress concentrations at re-entrant corners, often combined with inadequate lintel bearing, missing sill bands, or weak mortar joints. The 18 mm joints and unfilled perpends reduce bond and increase shrinkage movement. These are mainly workmanship defects, but the crack pattern must be checked by a structural engineer before plastering because a foundation or lintel deficiency cannot be corrected by cosmetic repair.
Triage: Test brick efflorescence and mortar cubes; open one joint to check bond; monitor crack widths for two weeks. Do not classify the wall as acceptable until the source of moisture is found. Material and workmanship defects can be repaired; a moving or wide crack is a structural hold point.
2. Assess the mason’s proposal to acid-wash and cement-paint immediately. Give a safe repair sequence and acceptance criteria before plastering.
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The proposal is not acceptable as a first response. Acid washing can attack cement mortar and does not remove the source of salts. Cement paint over damp, salt-laden masonry traps moisture and will blister, so it only hides the symptom.
A safer sequence is:
- Dry-brush the efflorescence and record its extent.
- Find and cut off the moisture path: raise the brick stack, check plinth damp-proof course, roof and pipe leakage, and site drainage.
- Cut out hollow or unbonded joints and repoint with a compatible 1:4 or specified mortar, filling perpends.
- Rake and fill hairline cracks; if cracks are active or wider than about 0.3 mm, stop and refer to the structural engineer.
- Allow the wall to dry, then carry out a wetting-and-drying check to see whether salts return before plastering.
Acceptance before plaster: joints nominally 10 mm, perpends filled, wall plumb and straight within project tolerance, no active crack, and no recurring efflorescence after the drying check. Record all readings and photographs.
3. What records and tests would you require, and what would you report to the client about occupancy?
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Required records: brick efflorescence and water-absorption test reports, sand silt test, mortar cube results at 7 and 28 days, joint and straightedge readings, crack-monitoring dates, and photographs showing the brick stack and repaired areas. Also record the damp-proof course and any water source found near the wall.
For the client, I would separate the decisions. Occupancy of the affected lower floor should be conditional, not refused outright, if the cracks are dormant, the damp source is corrected, and repairs are monitored. The upper floor and areas away from the damp wall can be considered separately. However, if a crack is progressive, if the lintel bearing is inadequate, or if mortar cube strength is clearly below specification, I would withhold acceptance until the structural engineer signs off.
The report should state what is known, what is assumed, and what remains a hold point. It should not promise that paint will solve the problem, because the client needs a durable repair before the monsoon, not a cosmetic cover.