Neil Turner at Ecological Building Systems explores how natural thermal plaster products can achieve modern thermal performance requirements without compromising on the original architecture of traditional buildings.
When it comes to renovating older properties, the challenge often lies in selecting materials that not only enhance thermal performance but are also sympathetic to the building’s authentic character and architectural features.
Thermal plasters are made from a combination of cork, lime and natural materials which creates a capillary active layer that can significantly improve the thermal performance of traditional solid walls.
BREATHABILITY
One of the main advantages of using thermal plaster is its hygrothermal properties. Hygrothermal performance describes a material’s ability to manage moisture and temperature. Natural thermal plasters can absorb and release moisture without compromising the integrity of the building. This breathability is essential in older properties, where trapped moisture can lead to structural damage and health issues due to mould growth. By using a moisture resistant and breathable thermal plaster, it can ensure that properties retain good levels of indoor air quality.
When applied internally, breathable thermal plasters can help create warmer and more comfortable living spaces while managing humidity levels. Externally, they act as an insulating layer that protects the building from temperature fluctuations throughout the year, therefore maximising comfort for occupants.
PRESERVING ARCHITECTURAL CHARACTER
One of the primary concerns when renovating older properties is improving energy performance without compromising architectural character.
Natural thermal plaster offers an approach that is compatible with historic fabric and can be applied in a way that retains the original features of a building. For example, they can be shaped to follow the contours of stonework or curved walls, ensuring that the aesthetic integrity of the property is preserved.
There are many examples of renovated buildings that have successfully used thermal plaster to enhance both performance and appearance. In the renovation of a Grade II farmhouse in the Lake District, Diasen Diathonite Thermactive.037, a lime and cork-based insulating plaster, was applied to help improve thermal efficiency while maintaining the building’s historic character. Because the material is capillary-active and highly vapour-open, it is well-suited for use in older solid-wall buildings. The plaster helps walls to regulate moisture and dry naturally, reducing the risk of condensation and mould while providing very good
thermal performance.
Thermal plaster is known for taking an extended time period to dry. However some of the latest modern lime and cork plasters have been designed with high levels of breathability, which also speeds up drying times. Some thermal plasters dry at a rate of 2mm per day (this may vary depending on ambient temperature or weather conditions), whereas conventional lime plasters dry at around 1mm per day.
THERMAL PERFORMANCE
A 50mm application of thermal plaster can enhance a wall’s thermal performance by up to four times, and its elasticity, which is around 10 times greater than that of conventional plasters, helps to prevent cracking and supports the long-term durability of the restored building.
The plaster should be applied in layers 15-25mm thick. The total thickness needed will depend on the required U-value for the specific project but 40-60mm is typical for the most cost-effective thermal improvement.
Thermal plasters like this are often specified as part of a wider retrofit strategy to help manage moisture while improving thermal performance. This allows the building to be upgraded to modern performance requirements while retaining vapour-open, compatible materials.
SUSTAINABILITY
Thermal plasters are often produced from renewable materials, which makes them a more sustainable choice compared to synthetic alternatives. As a result, they offer a reduced carbon footprint and typically require less energy to produce. They can also help improve indoor air quality, as many natural plasters are low in volatile organic compounds (VOCs), contributing to healthier living environments. Once applied, thermal plaster also requires minimal maintenance.
FINAL THOUGHTS
Choosing natural thermal plaster for renovated properties is crucial for achieving optimal thermal performance without compromising the building’s character.
Incorporating thermal plaster into renovation projects offers a unique opportunity to enhance energy efficiency while preserving the beauty and integrity of traditional architecture. As older buildings are increasingly being renovated to enhance their energy efficiency, innovative advanced types of thermal plaster will play a vital role in the future of sustainable buildings.
Neil Turner is UK technical manager at Ecological Building Systems