Internal lime plastering is a time-tested technique that offers numerous construction benefits, such as blending durability, moisture regulation, and eco-friendliness.
This method uses a mixture of lime, sand, and water. It is known for its breathability and flexibility, making it suitable for modern and historic structures.
Key advantages include preventing mould growth, self-healing minor cracks, and maintaining indoor air quality. Following precise preparation, mixing, and application steps is crucial for achieving optimal results.
Lime plastering enhances a building’s aesthetic and supports sustainable practices, ensuring long-lasting performance and environmental responsibility in architectural projects.
Let’s get straight to the point.
Lime plastering is a traditional, eco-friendly building technique that regulates moisture, is durable, and resists mould. It’s also breathable, flexible, and can self-heal minor cracks, making it ideal for historic and modern buildings.
Lime plaster is a sustainable choice because of its low carbon footprint, recyclability, and energy efficiency. Proper wall preparation, suction management, and application techniques are essential for achieving the best results.
Its natural aesthetics and compatibility with other materials enhance indoor air quality and reduce long-term maintenance costs.
Understanding Lime Plaster
Lime plaster is a traditional building material made from lime, sand, and water. It has been used since 8000 BC and is known for its breathability, allowing moisture to evaporate naturally.
This characteristic makes it ideal for buildings made from porous materials like stone or brick, where moisture regulation is vital.
Key Benefits Of Lime Plaster
1. Moisture Regulation
- Breathability: Lime plaster allows walls to “breathe,” regulating humidity levels by absorbing excess moisture from the air and releasing it when conditions are drier. This natural ventilation reduces the risk of trapped moisture, which can lead to structural issues.
- Mould Resistance: Its moisture-regulating properties help prevent the growth of mould and mildew. Unlike some modern plasters, lime’s high pH naturally resists fungal growth, creating a healthier indoor environment.
2. Durability
- Flexibility: Lime plaster is more flexible than modern cement-based plasters, allowing it to withstand minor structural movements without cracking. This elasticity is essential for older buildings where walls may shift over time.
- Self-Healing Properties: Lime plaster can self-heal small cracks through autogenous healing. When moisture is exposed, the plaster’s free lime can re-crystallize, filling in minor gaps and extending the plaster’s lifespan.
- Weather Resistance: Lime plaster is excellently resistant to harsh weather conditions for external use. It protects walls from rain and frost damage while maintaining their structural integrity.
3. Eco-Friendly
- Low Carbon Footprint: Lime plaster production generates significantly less carbon dioxide than gypsum and cement-based plasters, making it a more environmentally responsible choice.
- Recyclable and Biodegradable: Lime plaster is fully recyclable and breaks down naturally without releasing harmful chemicals into the environment. Old lime plaster can be crushed and reused, reducing construction waste.
- Energy-Efficient: Lime plaster’s thermal mass properties help to regulate indoor temperatures by absorbing and slowly releasing heat. This passive cooling and heating effect can reduce energy consumption in buildings.
4. Versatility And Aesthetic Appeal
- Wide Range of Finishes: Lime plaster can be applied in various textures, from smooth and polished to rough and rustic, making it a versatile choice for different architectural styles.
- Natural Aesthetic: Its natural tones and ability to age gracefully give buildings a timeless, classic look. It also accepts pigments, allowing for various colours without synthetic paints.
- Compatibility with Natural Materials: Lime plaster is compatible with other natural building materials, such as stone, brick, and wood, enhancing the overall aesthetic and integrity of eco-friendly designs.
5. Health Benefits
- Improved Indoor Air Quality: Lime plaster does not emit harmful volatile organic compounds (VOCs) like some synthetic plasters and paints. Its natural components contribute to better indoor air quality and a healthier living environment.
- Allergy Reduction: Lime plaster can help reduce allergens by regulating indoor humidity and preventing mould growth, making it an excellent choice for people with respiratory conditions or allergies.
6. Cost-Effectiveness
- Low Maintenance: Lime plaster’s durability and self-healing properties require less maintenance and fewer repairs over time, saving on long-term costs.
- Long Lifespan: When properly applied and maintained, lime plaster can last centuries, making it a more cost-effective solution than modern plaster alternatives that may need frequent replacements.
7. Historical And Cultural Significance
- Preserving Heritage: Lime plaster has been used for centuries in historic buildings, and its use today helps preserve traditional craftsmanship and architectural techniques.
Restoring old buildings with lime plaster maintains their original character and integrity.
- Cultural Continuity: Its application supports the continuity of ancient building traditions, bridging the gap between historic preservation and modern sustainable practices.
Incorporating these benefits into the discussion highlights lime plaster as not just a building material but an important element in sustainable, durable, and health-conscious construction practices.
Its versatility, natural properties, and long-term value make it an outstanding choice for traditional restorations and contemporary eco-friendly projects.
Types Of Lime Plaster
There are two main types of lime plaster:
- Non-Hydraulic Lime: This requires exposure to air to set and is best suited for dry environments.
- Hydraulic Lime: It uses a chemical reaction with water, making it ideal for damp or exterior applications, such as cellars or external walls.
Step-By-Step Guide To Lime Plastering
Steps For Wall Preparation
Before applying lime plaster, proper surface preparation is essential to ensure a durable and long-lasting finish:
- Clean the Surface: Remove any dirt, debris, or plant growth from the wall.
- Repair Damage: Fix any cracks or damaged masonry to create a smooth, solid base.
- Level the Wall: Use lime mortar to fill gaps or uneven areas.
Skipping these steps may result in poor plaster adhesion, reducing durability and weakening bonds.
Managing Wall Suction
Suction refers to the wall’s ability to absorb water, significantly impacting plastering. Here’s how to control it:
- High Suction (excess water absorption): Lightly dampen the wall before applying plaster to reduce suction.
- Low Suction (minimal water absorption): Apply additional water to the wall to increase absorption.
Balancing suction ensures an even finish and prevents the plaster from drying too quickly.
Mixing Lime Plaster
For the best results, follow these steps to mix lime plaster properly:
- Initial Mix: Mix the ingredients for at least 5 minutes.
- Slaking: Let the mixture rest for 3-5 minutes.
- Final Mix: Mix again for 2 minutes before applying.
This process ensures proper hydration and makes the plaster easier to apply.
Application Process
1. Base Coat (Scratch Coat)
- Mix Ratio: 1 part lime to 2.5 parts sand.
- Apply a thick base layer to the wall.
- Scratch key lines into the surface to help the next coat adhere.
- Lightly mist the surface to maintain moisture.
2. Floating Coat
- Apply a thinner layer (2-5 mm) to smooth out imperfections.
- Use a wooden or sponge float to achieve the desired texture.
3. Final Coat
- Mix Ratio: 1 part lime to 3 parts sand for a smooth finish.
- Apply thin layers, allowing each to dry slightly before adding the next.
- Lightly mist the surface between layers to manage suction.
Dealing With Common Issues
Hardened Plaster
Unlike cement-based plasters, lime plaster can be retempered (mixed again with water) if it hardens during application without compromising its final strength.
Salt Contamination
Salt in masonry can damage lime plaster. To manage salt buildup:
- Dry the Wall: Allow the wall to dry thoroughly.
- Poultice Application: Use a clay or lime poultice to draw out excess salt.
Avoid washing the wall, which can drive salt deeper into the masonry.
Maintenance And Preservation
Regular maintenance extends the life of lime plaster:
- Routine Inspections: Check for cracks or damage, especially in high-humidity areas.
- Retempering: Lime plaster can be softened with water and reused, even after it has started to harden.
Enhancing Texture And Appearance
Lime plaster offers flexibility in finishes:
- Troweling: Creates either a smooth or textured surface.
- Brushing: Adds unique patterns to the plaster.
The type of sand used also affects the texture. Use sand with sharp grains and varied sizes for better bonding and a strong finish.
Conclusion
In conclusion, internal lime plastering is more than a traditional building technique—it’s a versatile and sustainable solution that enhances the performance and aesthetics of modern and historic structures.
Its unique properties, such as breathability, durability, and eco-friendliness, make it a valuable choice for creating healthy, energy-efficient indoor environments.
Following the right preparation, mixing, and application steps, lime plaster can offer long-lasting benefits, reduce maintenance costs, and support sustainable construction practices.
Whether preserving a historic building or designing an eco-friendly home, lime plaster remains a timeless and reliable choice.
Frequently Asked Questions About Plaster
What Is Lime Plaster?
Lime plaster is composed of sand, water, and lime, usually non-hydraulic hydrated lime, also known as slaked lime, high calcium or air lime. Ancient lime plaster often contained horse hair for reinforcement and pozzolan additives to reduce the working time.
How Do You Fix Internal Lime Plaster?
If you have cracks internally or externally – slightly open up the crack, and you can use casein filler. The surfaces should be clean and grease-free. Water-soluble old coats of distempers or lime paints must be removed. Any loose material should be brushed off.
Why Is Lime Plaster No Longer Commonly Used?
Non-hydraulic lime plaster requires moisture to set and can be prevented from drying for several days. Unfortunately, the number of qualified tradespeople capable of plastering with lime is in decline due to the widespread adoption of drywall and gypsum veneer plaster.
Is Lime Plastering Difficult?
Lime plastering requires patience and a little know-how to achieve a beautiful, functional and long-lasting lime plaster finish.
How Thick Should Lime Plaster Be?
This coat is applied in a coat of approximately 10mm thickness. It can be applied using a steel trowel or thrown onto the wall by using a harling trowel and then flattened in by the steel trowel.
