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Moss*Crete

Exploration of surface geometry on moss growth

Nano, Micro, Macro: Biofabrication
Spring 2023
Harvard GSD
Instructors: Martin Bechtold, Daniel Tish

Team: Tobi Fagbule, Leonard Palmer, Jie Zheng
A living facade is a vertical surface incorporating vegetation into its structure or face to facilitate various aesthetic, environmental, social, or economic functions and benefits, including: Reduced energy consumption, improved air quality, reduced stormwater runoff, aesthetic benefits, noise reduction1. Moss*Crete is an investigation of living facades - particularly, concrete facades with moss growing on them. The existing research on moss on concrete has tested only on flat surfaces1. While moss does grow on flat surfaces, there may be specific forms of surfaces that help with moss growth. This project explores the possibilities of surface geometries and its effects on the rate and volume of moss growth. If there are correlations between surface geometries and moss growth, there would be design opportunities to create specific areas of the façade to intentionally attract or prohibit moss growth. In this way, the bio-receptivity of the concrete is manifested as part of the design of buildings, as opposed to an additional component that is independent from design.

As facade panels, the Moss*Crete panels can be arranged in different configurations depending on aesthetic and thermal needs. While the initial motivation of this project stemmed from introducing moss to concrete specifically because of its ubiquity in the building industry, the flexibility of application opens up opportunities for using materials other than concrete, like terracotta.
Sample panel of Moss*Crete
Three basic surface geometries were designed to create particular conditions that moss is attracted to. Permutations of these three basic geometries created four more types of panels. A total of seven surface geometries were tested. All panels are 0.25" at the thinnest part. The Ridges are inspired by tree roots in forests where moss is typically found. It’s speculated that the crevices in between the ridges create ideal conditions for the moss to grow. Moss also favors shaded areas. The Shading panels follow the conventions of horizontal louvres found in building facades that control the solar radiation that enters the building. The saw tooth form creates strands of shade on the panel itself. We also tested panels with holes in them to see if they help with the water retention, because moss is attracted to moist conditions. The air flow through the holes could also be beneficial for moss growth.
The panel molds were milled into 2” thick blue foam with the CNC machine. The toolpaths were calibrated to produce a rough texture, so that the cast concrete panels would have a rough surface. This has been found to be ideal for biological growth. The expanded clay balls were crushed with a hammer to produce the appropriate scale for the 6”x 6” panels. This crushed clay was then added into the cement, along with water. This produced our moisture capturing concrete mix.
The mold was prepared for casting by coating the surface with a layer of Murphy’s Oil Soap as the extract agent. The concrete mix was then pressed into the blue foam mold with a spatula, scraping the top off in order to have the backside of the panels flat. Once cured, the concrete was sanded at the top, then released from the mold. While most molds were reusable, the molds that included holes had to be destroyed for extraction.
The collected moss was soaked and rinsed with filtered water to eliminate the excess dirt. The moss was blended with a blender. Yogurt was added to the moss, then blended further. In our first attempt, we let the moss slurry rest for two days in order to let the moss produce spores. However, this resulted in a layer of mold at the surface of the slurry, ruining the mixture. In our second attempt, we immediately applied the slurry onto the concrete panels.
Before applying the moss/chia to the panels, the panels were soaked in water. This enabled a smooth application of the slurry onto the panels and ensured enough moisture was embedded in the panels. The slurry and goo were evenly applied onto the panels with a small paint brush. In order to retain the moisture, each panel was placed into a plastic sealable ziplock bag. This created a mini-greenhouse for each panel. All panels were placed in a room with indirect sunlight, to prevent too much solar radiation hitting the panels, especially because moss typically grow in areas where there’s not a lot of direct sunlight.
A small amount of moss was scraped off of the Moss*Crete (moss) panel for SEM imaging. The SEM images show various organisms, including what seem to be moss spores and mold spores. The strands of moss leaves are also visible, with spores grabbing onto them.
Thermal imaging of Moss*Crete panels (from left: concrete, Moss*Crete (moss), Moss*Crete (chia)). The flat panels of concrete, Moss*Crete (moss), and Moss*Crete (chia) showed a significant surface temperature difference. This aligns with our predictions of how moss growth would mitigate the heat on building surfaces. In future studies, it would be meaningful to capture thermal imaging of each of the surface geometry types once the moss and chia have shown significant growth. We can also measure the surface temperature of the back side of these panels to see how much heat transfers from the outer side of the panel into the inside.
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