What Is Fat Lime?
Fat lime is also called Rich lime, High calcium lime, Pure lime, White lime. It is obtained by calculating limestones.
When water is added to this lime, it produces hissing sound, a lot of heat is liberated it cracks and its volume is increased by 2-3 times the presence of air is essential for its setting. Hence it does not set.
- Under water.
- Below Ground.
- In interior joints of a thick wall.
It is used for white-washing, plastering and filling thin joints. Fat lime is highly plastic and is soluble in water.
To improve its hydraulic property, fat lime is mixed with surkhi (Brick powder) such mortar can set even in the absence of air and hence can be used for joints of thick, walls, or works below ground.
What Is Hydraulic Lime?
This lime does not require Co2 from the atmosphere for the setting. Hence it can set under-water. It is used in construction works. Strength is required.
This lime is not suitable for plaster-work because any unslacked particle may slake after some days causting blistering in plaster.
To improve this property this lime is ground to powder and then mixed with sand the mortar thus prepared is kept in a heap for about a week, and it is ground again. Such mortar prepared from hydraulic lime suitable for plaster-work.
Depending upon the percentage of clay content, hydraulic lime is divided into the following types,
Type of Hydraulic Lime.
- Eminently Hydraulic Lime.
- Moderately Hydraulic Lime.
- Feebly Hydraulic Lime.
1. Eminently Hydraulic Lime:
- Clay content – 21 to 30%
- Slaking – Slow with difficulty
- Setting – About 24 hours
- Hyraulicity – Eminent
- Uses – Can be used in important masonry works in place of cement
2. Moderately Hydraulic Lime:
- Clay content – 11 to 20%
- Slaking – After 1.5 hours
- Setting – About one week
- Hyraulicity – Moderate
- Uses – Masonry works
3. Feebly Hydraulic Lime:
- Clay content – 05Â to 10%
- Slaking – After few minutes
- Setting – Sets in water after about 3 weeks
- Hyraulicity – Feeble
- Uses – Ordinary masonry works.
Difference Between Fat Lime and Hydraulic Lime
| Detail | Fat Lime | Hydraulic Lime |
|---|---|---|
| Composition | More Percentage of CaO clay content less then 5% | Ca + clay content from 5 to 30 % and some % of iron oxide |
| Slaking | Slakes vigorously with hissing sound and cracking volume increased by 2 to 3 times slaking continues upto 3-4 hours. | Not much heat is liberated. No hissing sound or cracking volume increases by 1.2 times slaking continues up to 1-2 days |
| Setting | Sets slowly in presents of air. Absorbs CO2 from atmosphere and from CACO3. It does not have hydraulicity and hence can not set under water. | Sets under water – CaO content sets like fat lime calcium silicate & crystalline structures are formed they set like cement. It possesses hydraulidty. |
| Strength | It is not strong and hence can not be used where strength is requierd. | It is strong and can be used like cement |
| Use | Plastering, white washing preparing and mortar with surkhi mix. | Suitable for thick walls, works below ground in damp condition |
FAQ: Understanding Lime Types
What is the primary difference between fat lime and hydraulic lime?
Fat lime is predominantly composed of calcium oxide with minimal clay content, while hydraulic lime contains a higher percentage of calcium oxide along with varying amounts of clay, typically between 5 to 30%.
How does slaking differ between fat lime and hydraulic lime?
Fat lime undergoes vigorous slaking with hissing sounds, cracking, and a significant increase in volume, whereas hydraulic lime slakes with less heat, no hissing sound, and a moderate increase in volume.
What are the setting properties of fat lime and hydraulic lime?
Fat lime sets slowly in the presence of air by absorbing carbon dioxide from the atmosphere, while hydraulic lime sets under water due to the presence of hydraulicity, forming calcium silicate and crystalline structures similar to cement.
Which type of lime is suitable for plastering and white-washing?
Fat lime is suitable for plastering and white-washing due to its plasticity and solubility in water.
In what applications is hydraulic lime preferred over fat lime?
Hydraulic lime is preferred in applications requiring strength, such as thick walls, works below ground, or in damp conditions, where fat lime may not provide adequate strength.
Can fat lime be used in masonry works where strength is crucial?
Fat lime is not recommended for masonry works requiring strength, whereas certain types of hydraulic lime, particularly eminently hydraulic lime, can be used in place of cement for important masonry works.
How can the properties of hydraulic lime be modified for plaster-work?
Hydraulic lime can be ground to a powder, mixed with sand, and allowed to mature for about a week before re-grinding. This process enhances its suitability for plaster-work by reducing the risk of unslaked particles causing blistering in plaster.
What are the implications of clay content in hydraulic lime?
The clay content in hydraulic lime determines its hydraulicity and setting properties, with higher clay content resulting in greater hydraulicity and faster setting times. This classification includes eminently hydraulic lime, moderately hydraulic lime, and feebly hydraulic lime, each with distinct characteristics and uses.
Can fat lime set under water?
No, fat lime does not possess hydraulicity and cannot set under water. Its setting requires the presence of air and absorption of carbon dioxide from the atmosphere.
Which lime type is suitable for joints in thick walls or works below ground?
Hydraulic lime, particularly types with higher hydraulicity such as eminently hydraulic lime, is suitable for joints in thick walls or works below ground due to its ability to set in the absence of air.
