---
title: "Short note: hydraulic lime"
subject: "Civil Engineering Materials"
chapter: 4
key: "semester_3/civil_engineering_materials:hydraulic-lime-short-note"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/hydraulic-lime-short-note
site: BCT Engineering
---

# Short note: hydraulic lime

Civil Engineering Materials · Chapter 4: Lime

- Asked in: 2066 Shrawan (old course), 4 marks
- Video: [The Ultimate Guide to Mastering the Lime / Quick lime: Everything You Need to Know!](https://www.youtube.com/watch?v=YJIIvrQzCf8) — MFA Civil Engineering
- 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-lime-short-note
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-4

## Question

Write a short note on hydraulic lime.

## Short answer

Hydraulic lime contains 5–30% clay, enabling it to set underwater. Made by burning clayey limestone at 1000–1100°C, forming calcium silicates/aluminates. Classified as feebly, moderately, or eminently hydraulic by clay content; it sets slowly with higher strength than fat lime, used for damp masonry and foundations.

## Answer

**Hydraulic lime** is lime that contains clay (silica and alumina), usually 5 to 30%, so that it sets and hardens even under water.

#### Manufacture
Impure (clayey) limestone is burnt at 1000 to 1100 °C. Silica and alumina combine with lime to form calcium silicates and aluminates, which give the hydraulic properties.

#### Classification (by clay content)
- **Feebly hydraulic:** 5 to 15% clay.
- **Moderately hydraulic:** 15 to 25%.
- **Eminently hydraulic:** 25 to 30%.

#### Properties
- Grey or yellowish colour.
- Slakes slowly with little heat and small expansion.
- Sets in damp and underwater conditions, with higher strength than fat lime. The setting time depends on the clay content: about 1 to 2 days for eminently hydraulic lime, up to about 3 weeks for feebly hydraulic lime.
- Less affected by the atmosphere.

#### Uses
Mortar for masonry in foundations, damp places and thick walls, plastering of exposed surfaces, lime concrete and lime-surkhi mortar.

## Check yourself

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

1. Eminently hydraulic lime has clay:
   A. 25 to 30%
   B. 5 to 15%
   C. 15 to 25%
   D. Over 30%
   Answer: A. Feebly 5-15, moderately 15-25. (Key point: Clay content)

2. Hydraulic lime is burnt at:
   A. 100 degrees C
   B. 1000 to 1100 degrees C
   C. 300 degrees C
   D. 2000 degrees C
   Answer: B. Clayey limestone. (Key point: Burning)

3. It slakes:
   A. Violently
   B. Not
   C. Slowly with little heat
   D. Explosively
   Answer: C. Small expansion. (Key point: Slaking)

4. It is used for:
   A. Whitewash
   B. Glass
   C. Dry paint
   D. Foundations and damp places
   Answer: D. Also lime-surkhi mortar. (Key point: Use)

## 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×
- [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
- [Types of hydraulic lime](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Atypes-hydraulic-lime) — Civil Engineering Materials, chapter 4