Lime mortar is a type of mortar made from lime, sand, and water. It has been used in construction for thousands of years and was commonly used in Europe until the 19th century.
It has several advantages over modern cement-based mortars, including its ability to “breathe” or allow moisture to pass through it, its flexibility, and its compatibility with historic masonry.
Types of lime mortar
1. Non-hydraulic lime mortar
This mortar is made from pure lime and does not contain any additives. It sets slowly through the process of carbonation, which is the absorption of carbon dioxide from the air.
Non-hydraulic lime mortar is soft and flexible, making it suitable for historic restoration projects or buildings with movement.
It is not suitable for use in wet or humid conditions, as it will dissolve in water.
2. Hydraulic lime mortar
This mortar contains additives such as clay, which allow it to set through both carbonation and hydraulic action. This means that hydraulic lime mortar can set and harden even in wet or humid conditions.
It is suitable for use in both interior and exterior applications and can be used for historic restoration projects or new construction.
Hydraulic lime mortar comes in different types or strengths, such as NHL 2, NHL 3.5, and NHL 5, which indicate the ratio of lime to sand and the strength of the mortar.
Lime mortar mix ratio
The ratio of lime to sand varies depending on the intended use of the mortar.
Generally, a 1:3 or 1:4 ratio of lime to sand is used for most applications.
This means that for every 1 part of hydrated lime, you would use 3 or 4 parts of sand.
For example, if you want to mix a batch of lime mortar that requires 10 kg of hydrated lime and 30 kg of sand, you would use the following mix ratio:
- 10 kg hydrated lime
- 30 kg sand
- Water as needed to achieve desired consistency
IS code for lime mortar
The Indian Standard code for lime mortar is IS 1625:1971. This code of practice specifies the materials, proportions, and method of preparation of lime mortar for use in building construction in India.
Preparation of lime mortar
Materials:
- Quicklime (calcium oxide)
- Water
- Sand
Tools:
- Large container or mixing trough
- Garden hose or bucket for adding water
- Trowel or mixing tool
Instructions:
1. Wear protective gloves and goggles, as lime is caustic and can cause skin and eye irritation.
2. Measure out the amount of quicklime you need and add it to the mixing trough.
3. Slowly add water to the quicklime, mixing continuously with the trowel or mixing tool. The water-to-lime ratio depends on the type of lime and the intended use of the mortar. A common ratio is 1 part lime to 2.5 parts water by volume.
4. Continue adding water and mixing until you achieve the desired consistency. The mortar should be workable but not too wet or runny. If you are using sand, add it to the mixture and continue mixing until it is evenly distributed.
Note: Lime mortar should not be used in freezing conditions or where it will be exposed to continuous moisture, as it can degrade over time.
Advantages of lime mortar
1. Breathability
It allows for the free exchange of moisture between the building and the atmosphere. This helps to prevent the buildup of moisture within the walls, which can lead to decay and damage.
2. Flexibility
It is more flexible than other types of mortar, which allows it to expand and contract with the building as it settles and moves. This helps to prevent cracks and other types of damage.
3. Durability
It is very durable and can last for hundreds of years. This is because it is resistant to weathering, and can withstand exposure to the elements.
4. Self-healing
It can self-heal, which means that small cracks and defects can be repaired over time. This helps to maintain the integrity of the building over the long term.
5. Good workability and water retention properties
It is easy to work with and has good water retention properties, which makes it easier to apply and provides good adhesion to the building material.
6. Enhances brickwork and various masonry
It enhances the visual appearance of brickwork and masonry due to its natural and aesthetically pleasing color.
7. Can reduce the potential for water percolation
It can reduce the potential for water percolation into the walls of a building, which can cause damage over time.
8. Tends to reduce normal movement like thermal expansion etc.
It can expand and contract with the building, reducing the likelihood of cracking and damage due to normal movements like thermal expansion and contraction.
9. Can reduce the frost action
It is resistant to frost action and can help to protect the building from damage caused by freezing temperatures.
10. Reduces the need for movement joints
Due to its flexibility and ability to accommodate normal movements, lime mortar reduces the need for movement joints, which can simplify construction and reduce costs.
11. Makes use of much less energy to produce than cement
It requires less energy to produce than cement-based mortars, making it a more sustainable and environmentally-friendly choice.
12. Re-absorbs the CO₂ when it cures and sets
It can re-absorb CO₂ when it cures and sets, helping to reduce the environmental impact of the building process.
13. Permits masonry to be recycled at the finish of life
It allows for the easy recycling of masonry materials at the end of a building’s life, making it a more sustainable choice.
14. Provides a water-shedding barrier for walls
It provides a water-shedding barrier that helps to protect the walls of a building from moisture damage.
15. Offers constant prime quality and color of the mortar
It provides consistent quality and color, which enhances the visual appeal of the building.
Disadvantages of lime mortar
1. Less initial strength
It may have lower initial strength compared to cement-based mortars, which can affect the overall durability of the structure.
2. Quick setting time
It may have a quick setting time, which can limit the amount of time available for application and adjustment.
3. Not suitable for all building materials
It may not be suitable for all types of building materials, such as concrete or stone, which may require a stronger, more durable mortar.
4. Requires special application techniques
It requires specialized application techniques to ensure proper adhesion and to prevent cracking, which may require additional training or expertise.
5. More expensive
It may be more expensive than cement-based mortars due to the specialized materials and techniques required for proper application.
6. More maintenance required
It may require more maintenance over time compared to cement-based mortars, which may require periodic repointing or repair work.
Uses of lime mortar
1. Historic restoration
It is often used in the restoration of historic buildings, where its durability and compatibility with existing materials make it a preferred choice.
2. Bricklaying
It is often used in bricklaying due to its workability and ability to bond well with bricks and other masonry units.
3. Pointing
It is often used for pointing or repairing masonry joints, where its ability to accommodate movement and its breathable properties make it a good choice.
4. Plastering
It can be used for plastering both interior and exterior walls due to its ability to regulate moisture and its aesthetic appeal.
5. Garden walls
It is also commonly used in the construction of garden walls, where its durability and aesthetic appeal make it a good choice.
FAQ
What is lime mortar?
A lime mortar is a building material made from a mixture of lime, sand, and water. It is used as a binder to hold together masonry units such as bricks, stones, and tiles.
How does lime mortar differ from cement mortar?
Lime mortar is softer and more flexible than cement mortar, which makes it a better choice for historic restoration projects or buildings with movement. It is also more breathable, which can help to prevent moisture buildup and prevent damage to the masonry.
What are the advantages of using lime mortar?
Some of the advantages of using lime mortar include good workability, water retention, and reduction in movement such as thermal expansion. Lime mortar is also more environmentally friendly than cement, as it requires less energy to produce and re-absorbs CO2 when it cures.
What are the different types of lime mortar?
There are different types of lime mortar based on the type of lime used and the ratio of sand to lime. Some of the common types include non-hydraulic, hydraulic, and natural hydraulic lime mortar.
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