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Efflorescence causes and test

Short answer

Efflorescence is caused by soluble salts in brick earth or water crystallizing on the surface upon evaporation. In the lab test, the brick stands in 25 mm distilled water; after absorption and evaporation, the process is repeated, and white deposit coverage is rated from nil to serious.

What causes efflorescence in bricks and how is efflorescence in a brick determined in the lab?

Causes

Efflorescence is caused by soluble salts (sulphates and carbonates of sodium, potassium, calcium and magnesium) present in brick earth, in mortar water or in ground water. When moisture rises or enters the brick and evaporates, the salts remain as white crystals on the surface. Under-burnt bricks, poor quality water and salty soil make it worse.

Laboratory test

  1. Place the brick vertically in a shallow dish with 25 mm depth of distilled water, in a room.
  2. Let all the water be absorbed and evaporate. Then add the same quantity of water again and let it evaporate.
  3. Examine the brick for white patches.

Rating: nil (no deposit), slight (up to 10% of area covered), moderate (10-50%), heavy (more than 50%, without powdering) and serious (heavy, with powdering and flaking). Good bricks should show nil to slight efflorescence.

✓ Answer checked by Claude Opus 5.5 (high effort)

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