There is a lot of misunderstanding about mineral wool products used in the Green Roof Industry and Horticultural sector. It is time to correct some of the myths related to different products that are available on the market.
Due to their excellent water absorption, rock mineral wool fibres have been used for many years for different “green” applications including green roofs, green walls, landscaping, gardening and horticulture (hydroponics).
However, there were some drawbacks that were common to all rock mineral wool products on the market. These have led to some common misunderstandings, particularly related to some of the new innovative mineral wool products now available.
The best way to address some of the myths is to compare the old and new generation mineral wool products used as growing media. Knauf Insulation produces all of them so they know what’s best for which application.
1. What kind of Rock Mineral Wool (RMW) growing media can be found on the market?
Rock Mineral Wool products found on the market are characterised either by binding fibres together using different organic or inorganic binders, or by physical inter-connection of fibres. The three most common types are:
a. Traditional RMW growing media
 |
Traditional RMW growing media made by binding rock mineral fibres with phenol-formaldehyde based binders. As these binders make them hydrophobic, the RMW has to be coated with a special water absorbent coating to be used for growing vegetation |
b. Improved innovative RMW growing media with new generation of binders
 |
Improved innovative RMW growing media made by using a new generation of binders and more “eco-friendly” technology. A good example is Knauf Insulation’s Ecose® Technology binder (please see: www.ecosetechnology.com). However, these types of binders also make the product hydrophobic so water absorbent coating is still required to make them suitable for growing plants. |
c. Latest innovation in industry of RMW growing media - products without any binders
 |
The latest innovation in RMW growing media are products that require no binders at all. They are formed by a mechanical interconnection of pure mineral fibres. As the rock mineral fibres are hydrophilic, no special coatings are required to enable them to absorb water. |
2. Are rock mineral fibres hydrophobic?
Rock mineral fibres are in essence hydrophilic and not hydrophobic. They become hydrophobic only when they are transformed using different binders. When virgin rock fibres are used, water is simply absorbed by means of a physical attraction between rock fibres and the water.
3. Does rock mineral growing media lose its water absorption over time?
a. YES for traditional products
The water absorbent coating used to coat traditional rock mineral wool products can be washed away over time (usually in 1 to 2 years). This influences the water absorbent capacity of the RMW to the extent that it could become hydrophobic. The change process can be faster if the mineral wool has totally dried out.
b. NO for new generation products
Water absorbent capacity of products manufactured without binders is not affected over time as there is nothing to be washed away. The physical attraction between fibres and water remains the same throughout the lifetime of the products.
This information has been proven several times by independent studies based on pF tests for measuring water retention. Knauf Insulation has also been conducting real life tests for several years using all three types of RMW growing media in different applications in Europe as well as in North America.
4. Are rock mineral fibres dangerous?
NO!
When properly produced, rock mineral fibres are not problematic for health. There are extensive reports available supporting this fact1) All major global producers of mineral fibres are producing them according to the German quality mark and seal of the RAL Institute, (RAL) that is commonly used worldwide. Rock mineral fibres produced according to RAL are bio-soluble and are not dangerous to human health. More information on RAL can be found at www.ral-mineralwolle.de
The International Agency for Research on Cancer (IARC) has also evaluated the new generation of mineral fibres and has concluded that there is no significant evidence that rock mineral fibres are carcinogenic to humans2)
5. Is the water stored in rock mineral wool growing media available to plants?
Water stored in properly designed rock mineral wool substrates is nearly all available for plants to use. Independent research studies show that the majority of water inside the substrate is readily available for plant / sedum uptake. (University of Ljubljana, Biotechnical faculty). For measuring water retention, different methods for pF curve determination were used, from Sandbox to Hyprop.
1) For more details please refer to the information provided by Eurima (the European Insulation Manufacturers Association) at www.eurima.com and by Naima (North American Insulation Manufacturers Association) at www.naima.org
2) For more details please refer to the information provided by IARC (International Agency for Research on Cancer) ad www.iarc.fr
For more information on green roofs visit our website, subscribe to our Email Updates or download our Green Roof System Brochure:
And if you are interested in receiving a sample Performance evaluation report (all year's thermo-hydrological performance) of a basic roof design, in comparison with optimal Urbanscape Green Roof Design, for a selected town / country, please click here:
