Moss Concrete: A Feature of our Future?

By: Grace Choi

Image Credit: Fred Hsu, "Retaining wall covered in moss," February 2009, https://en.wikipedia.org/wiki/Moss#/media/File:Taiwan_2009_JinGuaShi_Historic_Gold_Mine_Moss_Covered_Retaining_Wall_FRD_8940.jpg[

When you think of a “green” building, what’s the first thing you think of? High powered-solar panels and sleek, modern surfaces?

How about a building that is quite literally . . . green?

On the side of buildings, moss is usually unwanted and visually unappealing. Not only that, moss is also a headache for homeowners, especially when attached to a roof: moss soaks up water and can cause leakages and rot. However, researchers in the Netherlands developed a way to grow a mat of moss onto concrete by using rhizoid moss, which does not damage the surfaces they grow on, creating “vertical moss landscapes.” 

Respyre has coined their creation the “Mosscrete,” which is a special type of concrete that is specialized for moss growth, creating a wonderful “green facade.” Not only pleasurable to look at, this moss concrete serves a plethora of functions: increasing air quality, reducing noise pollution, reducing load on drainage systems, and cooling down urban spaces while providing opportunities for biodiversity. Mosscrete can be plastered onto existing walls, and can be affixed to many different kinds of urban structures, such as sandwich panels, concrete walls, rooftops, and the sides of buildings. Respyre also offer different kinds of panels, such as Moss Sedum, which are easily placed onto roofs, and lightweight, insulated panels that have a variety of shapes and can easily be affixed to building surfaces. 

Bioreceptive concrete, such as Mosscrete, are built specifically for the growth of organisms in urban spaces, especially species of moss, lichen, and algae. Types of bioreceptive concrete are still being tested, especially because they come with many challenges. For example, it takes a long time for the bioreceptive concrete to become colonized by native organisms and show visible signs of growth. First, there is a layer of a bacterial and algal biofilm that can range from 10-20 micrometers, which then transitions into a cover of fungi and lichen that are a few millimeters long; this mat is not usually considered visually appealing. Only after these two stages does the “lower plants,” like moss, start colonizing the surface. These species tend to be very hardy, but the downside is that it takes a long time to grow and become aesthetically pleasing.

Although it is also possible to introduce spores beforehand and affix grown colonies to the building surfaces, the high mortality rate of these moss and other organisms in real, environmental conditions is another hurdle researchers must overcome. Specifically, the light and hydration must be optimized for the growth of the living mat, especially if the premade concrete fixtures move from indoor to outdoor conditions. 

These challenges make it hard for large-scale projects to arrive in the United States, especially because the moss species and techniques used for Respyre may work in the Netherlands and other European countries, but not in North America, where the climate and weather differs significantly. Currently, the United States does not have any large-scale moss concrete projects, but research is ongoing, meaning that green moss buildings still have the potential for becoming a new norm, especially as scientists set out to look for possible solutions.

For example, researchers in the Delft University of Technology in the Netherlands are looking at possible ways to make concrete more bioreceptive. Currently, known ways to increase bioreceptivity are high porosity and surface roughness, as well as water content, and adding phosphorus into the concrete mix. To increase phosphorus, bone ash from cattle was used in the experiment, and the researchers used different mixtures of concrete with water to increase porosity, magnesium sulfate to decrease pH, clay and combinations of each to test the varying factors. The result was that increasing surface roughness and adding bone ash lead to the most growth and cover of the concrete surfaces. These research projects allow for a future in which bioreceptive concrete allow urban spaces to flourish with life while supporting native organisms, whether it be plant, lichen, and algae species. 

Creating these vertical landscapes allow ecosystems to thrive in an increasingly urbanized world where native species may have eventually been pushed towards extinction. Not only a home for plants or algae, these spaces could also provide for insect and bird species, as well as microbes and their own micro communities. Furthermore, it could also improve the mental health of humans as well, as being exposed to more greenery is associated with better mental health, community connectedness, and boosts in creativity. As urbanization continues to increase in our world, vertical landscapes may not only support human comfort, but protect biodiversity and mitigate the effects of climate change, making them vital to the health of a future civilization.