Efflorescence and Hairline Cracks in a Coastal Brick Wall
At a two-storey residence near Digha, a mason is raising a 230 mm external wall 6.0 m long and 3.0 m high with local table-moulded bricks in 1:6 cement–sand mortar. The bricks are stacked on bare ground and are dipped in a water drum for barely a minute before laying. Joints are measuring 15–18 mm, and the wall is being raised about 1.5 m per day. The plinth filling used saline soil from a nearby creek, and no damp-proof course was provided. Three months after plastering, white powdery patches appear from the plinth up to about 600 mm, and hairline cracks run along the mortar joints. The owner blames the cement lot and wants the plaster redone with a richer mix. The site is 2 km from the sea and the water table is high.
1. The owner blames the cement. Assess that claim and explain the most probable cause of the white patches, including the mechanism by which they form.
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The cement is unlikely to be the main cause. The symptom is efflorescence, a crystalline salt deposit. The mechanism is: soluble salts dissolve in water, the water migrates through the masonry by capillary action, evaporates at the face, and the salts crystallise just below or on the surface.
Three sources converge here:
- Saline creek soil used as plinth fill supplies chlorides and sulphates.
- High water table plus no DPC gives a continuous capillary path upward.
- Unsoaked bricks and thick joints leave the mortar porous and poorly bonded, so moisture moves freely.
The distribution confirms this: the patches are strongest near the plinth and fade by 600 mm, which is exactly the pattern of rising moisture. A genuinely bad cement lot would show as weak, dusty mortar and low bond over the whole wall, not as salt at the base. Dry-brush the deposit, flush with clean water, let it dry and repeat; if it returns, cut out the plaster and provide a DPC. Test the cement only to rule it out.
2. Identify four construction practices in this work that are non-conforming, and state the corrected practice for each with reasons.
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Bricks dipped for one minute. They should be soaked in clean water until air bubbles cease (about 3–10 minutes for good bricks, longer for porous ones) and then surface-dried. Reason: dry bricks suck the mixing water out of the mortar, so the mortar never develops bond or strength.
Joints of 15–18 mm. The nominal joint should be 10 mm, uniform and fully filled. Thick joints mean more mortar, more shrinkage and lower compressive strength; they also make the brickwork look coarse.
Skipping the DPC and using saline fill. Provide a damp-proof course at plinth level - 40 mm cement concrete 1:2:4 with waterproofing compound, or a bitumen membrane - and use clean granular fill, not creek soil.
Bricks stacked on bare ground. Store on a raised, drained platform so the bricks do not absorb ground moisture and salts before laying.
A fifth point: the 1.5 m daily lift is at the upper limit. With green mortar it invites settlement cracks; keep lifts to about 1.0 m and keep the masonry moist.
3. Specify a simple field test and an acceptance criterion for the bricks, and a remedial treatment for the affected masonry before re-plastering.
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Brick test. Carry out the efflorescence test (IS 3495 Part 3): stand the brick on edge in a dish of clean water 25 mm deep, dry it in shade, and examine the surface. Rate it nil, slight, moderate, heavy. Acceptance: nil to slight efflorescence. Also check 24-hour water absorption - not more than 20% for common bricks, and not more than 15% for a better class.
Remedy for the masonry. Do not simply plaster over the salts.
- Dry-brush the deposits off, then wash with clean water and allow complete drying. Repeat for two or three cycles until the deposit stops returning.
- If salts persist, rake out the affected plaster and the outer 10–15 mm of mortar, and re-plaster with 1:4 cement mortar plus an integral waterproofing compound.
- Repair or install the DPC, because without it the source keeps feeding the wall.
- Keep the base of the wall clear of soil and provide a plinth protection apron sloping away.
Test the cement sample for fineness and mortar cube strength to close out the owner's claim, and record the results.