---
title: "Efflorescence causes and test"
subject: "Civil Engineering Materials"
chapter: 3
key: "semester_3/civil_engineering_materials:efflorescence-causes-lab-test"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/efflorescence-causes-lab-test
site: BCT Engineering
---

# Efflorescence causes and test

Civil Engineering Materials · Chapter 3: Clay Products

- Asked in: 2081 Baisakh (new course), 2 marks
- Video: [All About Efflorescence | Causes, Effect, Treatment | Civil Engineering for GATE & ESE 2024 | BYJU'S](https://www.youtube.com/watch?v=JXjrQ4mrcMg) — BYJU'S Exam Prep GATE & ESE: CE, ME & XE
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/efflorescence-causes-lab-test
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-3

## Question

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

## 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.

## Answer

#### 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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Efflorescence is caused by:
   A. Insoluble silica
   B. Soluble salts in earth, water or ground, left on evaporation
   C. Excessive burning
   D. Iron oxide
   Answer: B. Salts crystallise on the surface. (Key point: Cause)

2. In the lab test the brick is placed in a dish with:
   A. 250 mm of tap water
   B. Acid
   C. 25 mm depth of distilled water
   D. Oil
   Answer: C. The brick stands vertically in distilled water. (Key point: Test setup)

3. A good brick should show:
   A. Heavy efflorescence
   B. Serious efflorescence
   C. Moderate to heavy
   D. Nil to slight efflorescence
   Answer: D. Slight means up to 10% area covered. (Key point: Rating)

## Related in Civil Engineering Materials

- [Efflorescence test for bricks](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aefflorescence-test-brick) — Civil Engineering Materials, chapter 3
- [Efflorescence in bricks](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aefflorescence-in-brick) — Civil Engineering Materials, chapter 3, asked 2×

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