---
title: "Hydraulicity and lean lime"
subject: "Civil Engineering Materials"
chapter: 4
key: "semester_3/civil_engineering_materials:hydraulicity-lean-lime"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/hydraulicity-lean-lime
site: BCT Engineering
---

# Hydraulicity and lean lime

Civil Engineering Materials · Chapter 4: Lime

- Asked in: 2081 Kartik (new course), 1+1 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/hydraulicity-lean-lime
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-4

## Question

Define hydraulicity of lime. Write a short note on lean lime.

## Short answer

Hydraulicity is the property of lime to set and harden underwater due to reaction of CaO with clay (silica/alumina). Lean lime contains over 30% clay, slakes and sets slowly, yields a thin, weak paste, and is used for inferior mortar in dry conditions.

## Answer

#### Hydraulicity of lime
**Hydraulicity** is the property of lime that allows it to set and harden under water and in damp conditions, due to the reaction of calcium oxide with the clay (silica and alumina) present in it. It depends on the clay content, burning temperature and grinding.

#### Lean lime
**Lean (poor) lime** contains over 30% clay and other impurities. It slakes slowly, sets slowly, gives a thin paste of low strength and dirty grey colour. It is used for inferior mortar and plastering in dry conditions.

## Check yourself

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

1. Hydraulicity is the ability to:
   A. Dissolve
   B. Set and harden under water
   C. Burn
   D. Slake quickly
   Answer: B. Due to clay. (Key point: Hydraulicity)

2. Lean lime contains:
   A. Under 5% clay
   B. Pure CaO
   C. Over 30% clay
   D. Gypsum
   Answer: C. It is of low strength. (Key point: Lean lime)

3. Lean lime is used for:
   A. Underwater work
   B. Cement making
   C. Structural
   D. Inferior mortar in dry conditions
   Answer: D. It is weak. (Key point: Lean lime use)