Efflorescence in bricks causes due to
🧪 Understanding Efflorescence
Efflorescence is the crystalline, salty deposit that appears as a white, powdery layer on the surface of bricks, concrete, or other porous building materials. The phenomenon occurs when water carrying dissolved salts seeps to the surface of the material and then evaporates, leaving the salt crystals behind.
🔬 Detailed Analysis of the Options
D. present of soluble salt in parent clay
This is the correct answer. The fundamental cause of efflorescence is the presence of soluble salts (like sulphates of sodium, potassium, calcium, and magnesium) within the raw material, in this case, the brick clay. Without these salts, efflorescence cannot occur, regardless of other factors.
C. high porosity of the bricks
This is incorrect, but it describes a major contributing factor. High porosity provides the pathways (capillaries) for water to travel through the brick and carry the dissolved salts to the surface. However, if there are no salts to begin with, a porous brick will not show efflorescence. Therefore, porosity is an enabler, not the root cause.
A. excessive burning of bricks
This is incorrect. Excessive burning tends to vitrify the brick, making it less porous and thus *less* susceptible to efflorescence. It causes other defects like brittleness and dark colour.
B. high content of silt in brick clay
This is incorrect. A high silt content mainly affects the plasticity and strength of the brick. It is not the direct cause of the chemical salt deposits that constitute efflorescence.
📊 Summary: The Three Ingredients of Efflorescence
| Component | Role | Description |
|---|---|---|
| Soluble Salts | The Root Cause | The material that forms the white powder. |
| Water / Moisture | The Transport Medium | Dissolves the salts and carries them to the surface. |
| Porosity | The Pathway | Allows water to move through the brick. |
💡 Study Tips
- Efflorescence = Salts + Water + Pores: Remember this simple formula. All three must be present for it to occur.
- Distinguish Cause from Contributor: The presence of salt is the *cause*. Porosity is a *contributing factor*. This is a common distinction in exam questions.
- Think "Salty": Associate the visual of the white powder with the chemical concept of salts being left behind after water evaporates.