Which of the following types of lime is used for plastering and white washing?
🎨 Understanding Lime for Finishing Works
Different types of lime are suitable for different jobs. For finishing works like plastering and whitewashing, the ideal lime is one that is highly plastic (easy to spread), has excellent workability, and provides a smooth, bright white finish. Strength is less critical for these applications compared to workability and appearance.
🔬 Detailed Analysis of the Options
A. Fat lime
This is the correct answer. Fat lime (also known as pure lime or rich lime) is the ideal material for plastering and whitewashing. Its high purity (>95% CaO) gives it a brilliant white color. When slaked, it forms a highly plastic and workable putty that can be applied smoothly to surfaces. It hardens slowly by absorbing carbon dioxide from the atmosphere, resulting in a durable finish.
B. Slaked lime
This is a plausible but less precise answer. "Slaked lime" (or hydrated lime) is the powder form (Ca(OH)â‚‚) obtained after adding water to quicklime. While you must use *slaked* fat lime for plastering, "Fat lime" is the more fundamental answer that describes the *type* of lime with the desired properties of purity and plasticity.
C. Hydraulic lime
This is incorrect. Hydraulic lime is used for masonry mortar, especially in damp conditions or for structural work, because it sets by reacting with water. It is generally not as white, is less plastic, and can be too strong and brittle for a good plaster finish.
D. Quick Lime
This is incorrect. Quicklime (CaO) is the raw, unslaked material. It is highly caustic and must be slaked with water before it can be used for any construction purpose. Applying quicklime directly would be dangerous and ineffective.
📊 Summary: Lime Application Guide
| Lime Type | Primary Use | Key Property |
|---|---|---|
| Fat Lime | Plastering, Whitewashing, Finishing | High plasticity, white color, workability |
| Hydraulic Lime | Masonry Mortar, Foundations, Underwater Work | Strength, ability to set without air |
💡 Study Tips
- Fat for Finish: Remember this simple alliteration: "Fat lime is for finishing."
- Hydraulic for Hardness: "Hydraulic lime is for hardness and structural work."
- Distinguish Type vs. Form: Understand that "Fat lime" and "Hydraulic lime" are *types* based on composition. "Quicklime" and "Slaked lime" are *forms* based on whether water has been added yet. For plastering, you use the slaked form of fat lime.