We were intrigued by the social-media acclamations we witnessed recently relating to the development of products generically being referred to as “moss concrete”, especially since so many of us spend a lot of time and money trying to remove moss from our walls, driveways and patios. It is claimed that these developments offer environmental, thermal, biodiversity and aesthetic advantages, all of which are becoming very popular in our times of concern over climate change and biodiversity loss, so is this a potentially valuable concept to be adopted in mitigation of some development projects?
Our investigations have so far uncovered 3 different approaches.
One potential product, originally reported in about 2013, comprises 4-layered panels which can be fitted in a variety of patterns to new-build developments or during renovation projects. The layers include a cement structural foundation; an impermeable layer to prevent water migrating into the base layer and causing damage to it or even to the structure that the panel is fitted to; a biological layer, which helps retain water and supports the growth of the moss, and an outer layer which permits rain water to enter the biological layer, and prevents it from returning to the atmosphere outside. More recent reports suggest that work was underway to encourage the moss to establish a good coating within a year of introduction. However, we have found little evidence that the proposal has yet matured into a product, and all pictures we have seen have been simulations of installations.
Another product apparently consists of a concrete and plaster mix which can be applied as a coating to concrete structures and retains large amounts of water to support the growth of moss. Video simulations show remarkably lush and uniform growth, but, again, we haven’t yet discovered any feedback on any formal trial of this approach.
Meanwhile, trials of a different approach to encouraging green walls are already under way with a third project at 2 locations in London and 1 in Edinburgh. Here, small numbers of poikilohydric living wall panels, employing bioreceptive sculpted stone panels to retain mosses and lichens and to supply them with water, have been installed. The claims for such walls are similar to those for the moss concrete panels outlined above, but studies into their effectiveness are underway and won’t be completed for about 3 years. Once again, therefore, we can only wait and see.
In the absence of evidence or feedback from practical installations, we wondered about the likely effectiveness of these solutions, in particular their carbon absorption abilities.
The carbon sequestration properties of moss have been rightly trumpeted as more peat bogs have been reinstated, and such bogs are now thought to be able to absorb and store more carbon than equivalent areas of forest. However, scientists and ecologists repeatedly observe that this ability is based on the assumptions that moss layers are added over time, increasing the overall mass of material, and that none of the moss dries out or decays, at which point any absorbed carbon would be released to the atmosphere once again.
It is not clear how much moss these new solutions might support, but it seems likely that it would be a relatively thin layer when they are applied to vertical structures. It will thus be interesting to see an assessment of the period over which any of these solutions would actually act as a carbon dioxide sink. It would also be interesting to know how the retention of any growing moss will be affected by long-term exposure to the elements, especially the sun and wind, as well as to potential damage as birds investigate the mossy covering for the presence of spiders and insects. Judging from the numbers of small moss blobs strewn periodically on the floor around our garage roof, it seems that the long-term impact of moss concrete could be low.
The panel creators have acknowledged that such cladding would not be a universal solution, because the proposed plants will need a temperate Mediterranean climate to prosper. Equally though, given that mosses generally favour damp and shaded areas, these solutions might not be appropriate for brightly lit, south-facing structures.
However, until these potential solutions have had some medium-term field trials, we guess that the answers to most of our questions will not be known. Hopefully, such issues will be addressed during the commercialisation phase of product introduction, so we look forward to hearing more about the effectiveness of “moss concrete” solutions over the next couple of years.
JP Ecological Services 