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

# Hydraulic and fat lime properties

Civil Engineering Materials · Chapter 4: Lime

- Asked in: 2071 Chaitra, 2 marks
- Video: [Different Types of Lime |Fat Lime, Hydraulic Lime, Poor Lime |Civil Engineering |Diploma/Polytechnic](https://www.youtube.com/watch?v=QeQD8INsHNI) — Polytechnic Class (READBY) 
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/hydraulic-fat-lime-properties
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-4

## Question

Explain hydraulic lime and fat lime with their properties.

## Short answer

Fat lime (>95% CaO) is white, slakes violently, sets only in air and has low strength. Hydraulic lime (5–30% clay) is greyish, slakes slowly, sets under water and achieves higher strength.

## Answer

#### Fat lime
Pure quicklime with over 95% CaO.
- White colour, slakes with great heat and swelling.
- Sets slowly in air by absorbing CO₂, not under water.
- Low strength, high plasticity.
- Used for whitewashing and plaster.

#### Hydraulic lime
Limestone burnt with 5 to 30% clay.
- Greyish colour, slakes slowly with little heat and expansion.
- Sets under water and in damp places through hydration of silicates and aluminates, and gains good strength.
- Classified as feebly, moderately and eminently hydraulic.
- Used for mortar in foundations, damp places and masonry below ground.

## Check yourself

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

1. Fat lime is:
   A. White
   B. Grey
   C. Black
   D. Red
   Answer: A. Hydraulic is greyish. (Key point: Fat lime colour)

2. Hydraulic lime sets via:
   A. Carbonation only
   B. Hydration of silicates and aluminates
   C. Drying only
   D. Freezing
   Answer: B. It sets under water. (Key point: Hydraulic setting)

3. Hydraulic lime is classified as:
   A. Fat, poor, lean
   B. Hot, cold, warm
   C. Feebly, moderately, eminently hydraulic
   D. Soft, hard, brittle
   Answer: C. By clay content. (Key point: Classification)

## Related in Civil Engineering Materials

- [Fat lime versus hydraulic lime](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Afat-hydraulic-lime-difference) — Civil Engineering Materials, chapter 4, asked 3×
- [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
- [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
- [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
- [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