---
title: "Fat lime versus hydraulic lime"
subject: "Civil Engineering Materials"
chapter: 4
key: "semester_3/civil_engineering_materials:fat-hydraulic-lime-difference"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/fat-hydraulic-lime-difference
site: BCT Engineering
---

# Fat lime versus hydraulic lime

Civil Engineering Materials · Chapter 4: Lime

- Asked in: 2080 Baisakh, 3 marks; 2076 Asoj, 2 marks; 2059 Poush (old course), 4 marks (asked 3 times)
- Video: [Classification of Lime(Fat Lime,Hyrdaulic Lime,Poor Lime)//with main Points..](https://www.youtube.com/watch?v=_Mp6CqSnQrE) — Glowup Education
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/fat-hydraulic-lime-difference
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-4

## Question

Differentiate between fat lime and hydraulic lime.

## Short answer

Fat lime is made from pure limestone, slakes rapidly with heat and expansion, sets in air, and is white. Hydraulic lime contains 5–30% clay, slakes slowly, sets under water, has higher strength, and is grey or yellowish.

## Answer

| Basis | Fat lime | Hydraulic lime |
|---|---|---|
| Raw material | Pure limestone (over 95% CaCO₃) | Limestone with 5-30% clay |
| Slaking | Slakes rapidly with heat and large expansion | Slakes slowly with little heat |
| Setting | Sets in air by carbonation, slowly | Sets in water and damp places |
| Strength | Low | Higher |
| Colour | White | Grey or yellowish |
| Lumps of lime | Soft, easily break | Hard |
| Volume increase | 2 to 2.5 times | Less |
| Uses | Whitewash, plaster | Masonry mortar in damp places, foundations |

## Check yourself

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

1. Fat lime slakes:
   A. Slowly with little heat
   B. Not at all
   C. Only under water
   D. Rapidly with heat and large expansion
   Answer: D. Hydraulic lime slakes slowly. (Key point: Slaking)

2. Hydraulic lime sets:
   A. In water and damp places
   B. Only in dry air
   C. By carbonation only
   D. Never
   Answer: A. Fat lime sets slowly by carbonation. (Key point: Setting)

3. Fat lime increases volume by:
   A. Less than 1.1 times
   B. 2 to 2.5 times
   C. 10 times
   D. Remains the same
   Answer: B. Hydraulic lime increases less. (Key point: Volume)

4. Hydraulic lime colour is:
   A. Pure white
   B. Black
   C. Grey or yellowish
   D. Red
   Answer: C. Fat lime is white. (Key point: Colour)

## Related in Civil Engineering Materials

- [Hydraulic and fat lime properties](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Ahydraulic-fat-lime-properties) — Civil Engineering Materials, chapter 4
- [Quick lime versus hydraulic lime](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aquick-lime-hydraulic-lime-difference) — Civil Engineering Materials, chapter 4
- [Hydrated versus hydraulic lime](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Ahydrated-hydraulic-lime-difference) — Civil Engineering Materials, chapter 4
- [Fat lime composition, properties, uses](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Afat-lime-composition-properties-uses) — Civil Engineering Materials, chapter 4
- [Storage and handling of fat lime](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Astorage-handling-fat-lime) — Civil Engineering Materials, chapter 4
- [Short note: hydraulic lime](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Ahydraulic-lime-short-note) — Civil Engineering Materials, chapter 4

## Related in other subjects

- [Permeability versus hydraulic conductivity](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Apermeability-versus-hydraulic-conductivity) — Engineering Geology I, chapter 6