Lime – #Building Materials

Lime

1. Introduction

Lime is a binding material obtained by burning limestone and then processing it.
It is one of the oldest construction materials, widely used in mortar, plastering, whitewashing, and soil stabilization.

👉 In simple words: Lime is a cementing material made from limestone and used to bind bricks and stones.

2. Core Concepts
3. Raw Material of Lime

The main raw material is limestone (CaCO₃).

Other sources:

• Kankar
• Marble
• Shells

1. Manufacture of Lime

This is a very important exam topic.

Step 1: Calcination (Burning)

Limestone is burnt in a kiln at 900°C – 1000°C.

Chemical reaction:

 

• CaO = Quick lime
• CO₂ = Carbon dioxide

Step 2: Slaking

Quick lime is mixed with water.

 

• Ca(OH)₂ = Slaked lime

1. Types of Lime
2. Fat Lime (Rich Lime)

• Contains 90–95% calcium oxide
• Sets slowly in air
• High plasticity

Use: Whitewashing, plastering

2. Hydraulic Lime

• Contains clay and silica
• Sets in water and air
• Stronger than fat lime

Use: Masonry, foundations

3. Poor Lime

• High impurities
• Weak strength

Use: Temporary works

1. Properties of Good Lime

A good lime should:

• Slake easily with water
• Form smooth paste
• Set in reasonable time
• Have good strength

1. Uses of Lime

Use	Purpose
Mortar	Brick masonry
Plaster	Wall finishing
Whitewashing	Surface coating
Soil stabilization	Road works

3. Step-by-Step Practical Examples

Example 1: Identifying Type of Lime

Question:
A lime sets under water and is used for foundations. Identify the type.

Step 1: Observe property

Sets under water.

Step 2: Match with type

Hydraulic lime sets in water.

➡ Answer: Hydraulic lime

Example 2: Chemical Process in Lime Making

Question:
What happens when limestone is heated?

Step 1: Write formula

Limestone = CaCO₃

Step 2: Apply heat

 

Step 3: Identify product

CaO = Quick lime

➡ Limestone changes into quick lime

4. Visual Aid Description (Diagram / Flowchart)

Title: Manufacture of Lime

Flowchart:

Limestone → Burning (Kiln) → Quick Lime → Slaking with Water → Slaked Lime

Each step in a box connected by arrows.

This diagram helps remember the sequence easily in exams.

5. Exam Focus: Must-Know Points ⭐

• Lime is obtained by burning limestone.
• Quick lime = CaO, Slaked lime = Ca(OH)₂.
• Hydraulic lime sets under water.
• Fat lime has high plasticity but low strength.
• Burning temperature of limestone = 900°C – 1000°C.

6. Multiple Choice Questions (MCQs)
7. Main raw material for lime is:
8. Clay
   B. Limestone
   C. Sand
   D. Gypsum

Answer: B

Explanation: Lime is obtained by burning limestone.

2. Chemical formula of quick lime is:
3. CaCO₃
   B. Ca(OH)₂
   C. CaO
   D. CaSO₄

Answer: C

Explanation: Quick lime is calcium oxide (CaO).

3. Slaked lime is obtained by adding:
4. Sand
   B. Water
   C. Cement
   D. Clay

Answer: B

Explanation: Water reacts with quick lime to form slaked lime.

4. Which lime sets under water?
5. Fat lime
   B. Poor lime
   C. Hydraulic lime
   D. Rich lime

Answer: C

Explanation: Hydraulic lime sets in air and water.

5. Chemical formula of slaked lime is:
6. CaO
   B. CaCO₃
   C. Ca(OH)₂
   D. CaSO₄

Answer: C

Explanation: Slaked lime is calcium hydroxide.

6. Burning temperature of limestone is:
7. 200°C – 400°C
   B. 500°C – 700°C
   C. 900°C – 1000°C
   D. 1300°C – 1500°C

Answer: C

Explanation: Proper calcination occurs at 900°C – 1000°C.

7. Which lime is used for whitewashing?
8. Hydraulic lime
   B. Fat lime
   C. Poor lime
   D. Cement lime

Answer: B

Explanation: Fat lime has high plasticity and smooth finish.

8. Quick lime reacts with water and releases:
9. Light
   B. Cold
   C. Heat
   D. Gas

Answer: C

Explanation: Slaking is an exothermic reaction.

9. Which lime has maximum purity of calcium oxide?
10. Poor lime
    B. Hydraulic lime
    C. Fat lime
    D. Slaked lime

Answer: C

Explanation: Fat lime contains 90–95% CaO.

10. Lime is mainly used as:
11. Aggregate
    B. Binding material
    C. Reinforcement
    D. Fuel

Answer: B

Explanation: Lime binds bricks and stones in mortar.