The Environmental Impact of Polypropylene Fibre in Lime Plaster

When it comes to heritage building materials, lime plaster is often favoured due to its breathability, durability, and low carbon footprint. Traditionally, lime plaster has been reinforced with animal hair (often horse or goat) to improve its tensile strength and resilience. However, in recent years, there has been a growing trend to use synthetic fibres, particularly polypropylene, as an alternative - a practice that has been used in concrete production for years.

This shift raises a key question: given the increasing concerns around the use of microplastics, how do these two reinforcement materials compare from an environmental perspective? This blog sets out some of the ecological implications of using polypropylene fibre in lime plaster instead of traditional animal hair.

Horse hair being added to wet lime plaster

Horse hair mixed into wet lime plaster

Production Process and Resource Use

• Polypropylene Fibre: Polypropylene, a plastic polymer, is derived from fossil fuels, primarily petroleum. Its production process is energy-intensive, and extracting the raw materials for polypropylene is a significant source of greenhouse gas emissions. Manufacturing the fibre releases carbon dioxide and other pollutants, contributing to the overall environmental burden. However, some polypropylene fibres can be sourced from recycled plastics, which reduces the demand for virgin petroleum products, but still involves energy-intensive recycling processes. When it comes to its practical use, polypropylene fibres do not dissolve in alkaline plaster if stored wet and so can be pre-mixed saving considerable time on site.

  
  

• Animal Hair: The environmental footprint of animal hair as a reinforcement material is significantly lower. Harvesting animal hair involves minimal processing and requires no synthetic manufacturing steps. For example, horse hair is gathered as a by product of the regular hair clipping horses receive during their life. Additionally, it is biodegradable and can be sourced locally, reducing transportation emissions and limiting the need for industrial processing.

  
  

Winner: Animal hair has a clear advantage here, given its natural origin, minimal processing needs, and lack of fossil fuel dependence. However, a key reason polypropylene has gained ground in lime plasters is that it can be stored in wet plaster, saving time on site.

Durability and Longevity

• Polypropylene Fibre: Polypropylene fibres have a high tensile strength, making lime plaster more resistant to cracking and long-term wear. This can reduce the need for repairs and replacements, thereby minimising material consumption and waste over time. While polypropylene does not degrade in the same way that natural materials do, this durability in construction materials is sometimes seen as a benefit, as it helps maintain the structure longer.

  
  

• Animal Hair: While durable in its own right, animal hair is more susceptible to degradation over time, particularly in humid or damp environments. This can result in a slightly shorter lifespan compared to polypropylene, potentially requiring more frequent repairs. However, since lime plaster itself is highly durable, many historical buildings still stand today with animal-hair reinforced plaster, proving it to be a long-lasting choice.

  
  

Winner: Polypropylene fibre has the edge in terms of longevity, though the difference may be marginal depending on the environment and care taken in building maintenance.

Biodegradability and Disposal

• Polypropylene Fibre: One of the main environmental drawbacks of polypropylene is that it is not biodegradable. Polypropylene fibres can persist in the environment for hundreds of years, contributing to microplastic pollution. When construction materials containing polypropylene reach the end of their life, they are typically sent to landfill, where they can contribute to plastic waste.

  
  

• Animal Hair: Animal hair is completely biodegradable and poses no environmental hazards if it ends up in landfills or other disposal areas. When lime plaster reinforced with animal hair is eventually demolished or broken down, the hair decomposes naturally, returning nutrients to the soil without leaving behind harmful residues.

  
  

Winner: Animal hair, as a biodegradable material, is significantly more environmentally friendly at the end of its lifecycle.

Polypropylene fibres

Local Sourcing and Transportation

• Polypropylene Fibre: Polypropylene is typically manufactured in large industrial facilities, which may be located far from construction sites, resulting in additional transportation emissions. However, some companies do source recycled polypropylene from local recycling plants, reducing the environmental cost of shipping raw materials.

  
  

• Animal Hair: Animal hair can often be sourced locally, especially in regions with a strong equine or other livestock industry. Using local resources reduces transportation emissions and also supports the local economy.

  
  

Winner: Animal hair, due to its local sourcing potential, typically has a smaller carbon footprint related to transportation.

Conclusion: The Green Choice in Lime Plaster Reinforcement

While polypropylene fibre is an effective and durable alternative for reinforcing lime plaster, animal hair remains the clear choice for those seeking the most environmentally friendly option. Here’s a recap of the environmental comparison:

• Environmental Impact of Production: Animal hair has a much smaller carbon footprint compared to polypropylene.

• Biodegradability: Animal hair is biodegradable, unlike polypropylene, which contributes to plastic waste.

• Local Sourcing: Animal hair is often available locally, reducing transportation emissions.

  
  

In summary, for heritage builders focused on sustainability, animal hair is a more eco-friendly and authentic reinforcement choice. Polypropylene may still appeal due to its durability, availability and ease of use, especially in settings where animal hair is difficult to source. However, if environmental impact is a key concern, sticking with natural, biodegradable materials like animal hair aligns better with eco-conscious building practices.