Building with Mushrooms

Along with our research on wool and cardboard insulation we turn towards investigating the constructional potential of living organisms, in the frame of our research on sustainable insulation. Our aim is to explore natural solutions that could replace conventional materials while being equally efficient, more ecologically responsible and cost competitive. In our latest research we have been focusing on the insulation properties of fungal mycelium and developing different kinds of prototypes to be tested and compared.

The major role of fungi in nature is to act as a decomposer. They grow on dead organic matter, disassembling and recycling it back to the environment. In fact, mushrooms are only the flower of the bigger organism that is basically formed by mycelium. Mycelium is the vegetative tissue of the fungus, the medium through which it absorbs nutrients. It can be found in abundance on the planet as it easily colonises soil and many other substrates, practically acting like a glue that binds together different natural particles.

In the world of construction and object making, it seems that mycelium technology has a lot to offer. It mainly consists of a process where an organic substrate is inoculated and gradually digested by the mycelium, forming a solid mass. Later in this process, the biological activity of the mycelium is terminated and the final material is produced. There have already been a few people and companies exploring the vast properties of mycelium in building construction, insulation, art and product design, resulting in more than promising solutions^[1].

The advantages of using fungal mycelium lie in the fact that it is 100% biodegradable as well as in its exceptional material properties. More specifically, the mycelium tissue can trap more heat than fiberglass insulation, it is fireproof, nontoxic, partly mold and water resistant and stronger pound for pound than concrete^[2]. Moreover when dried, it can become very light, depending on the used substrate and its density. The rapid growing, tight mycelium tissue can expand under a wide range of environmental conditions and therefore allows a fast, easy, low-cost and energy material production. Another characteristic is that, when placing two alive, individual mycelium bricks together, the mycelium will rapidly spread amongst them and become the bonding material.

On the other hand, one of the most important disadvantages of mycelium-based objects is that their water resistance decreases overtime and thus they become vulnerable to mold and humidity. Artist Philip Ross, cofounder of MycoWorks, mentions that the mycelium bricks survived the east coast winter with no coating and without touching the ground for several years, swelling and shrinking depending on the weather but still functional when dried out. However, when in contact with the ground a mycelium panel may start to decompose in about a period of six weeks^[3]. On the contrary, if maintained in favorable and stable conditions it can have a lifespan of approximately 20 years^[4]. What can serve as a general statement, is that mycelium behaves like untreated softwood, meaning that it will stay strong whilst inside but start decaying when overly exposed to changing weather conditions. Other than that, despite mycelium being stronger than concrete relative to its weight, its compressive strength of around 30 psi is far from comparable to the 4000 psi of concrete^[5].

The combination of different substrate and mycelium types obviously relates to the properties that the final material will develop and to the environmental conditions needed for it to reach its full potential. For example, Sebastian Cox and Ninela Ivanova used the mycelium of horse hoof fungus (fomes fomentarius), a mushroom that grows on tree trunks and therefore they chose to use woodchip waste (coppiced hazel and goat willow) as a substrate material for their furniture making. As a result they produced strong, lightweight and fully compostable furniture forms. Other types of strains that can be used as mentioned by Phil Ross are namely: Ganoderma lucidum, Ganoderma tsugae, Ganoderma oregonense, Trametes versicolor and Piptoporus betulinus. However there is one very common strain used mainly for its fast growth rates: the oyster mushroom (Pleurotus ostreatus).

When it comes to insulation, there are several factors that can affect the performance of a mycelium-based material. These — as mentioned before — are mainly the choice and combination of substrate and fungal strain. Generally, the final material will incorporate the properties of both actors. Some strains are more or less suitable because of the density and quality of the mycelium tissue they create. In the same way, each substrate has different mechanical properties, thermal and water insulation qualities. What is needed for an insulation material — as opposed to the compact formulation needed for a structural brick — is low density and porosity. Having a light-weight material is also important. Apart from the thermal properties of mycelium, the advantage of using mycelium-based products for insulation is that they do not have to be exposed to the outside environment which is the number one factor that would accelerate degradation. On the other hand, the biggest challenge is how to protect them from humidity and mold without destroying their compostability.

The principal limitation in using existing natural treatments like oil or waxes for insulation is that they do not consist a permanent solution, meaning that they need to be reapplied after a certain period of time. This would require for the panels to be easily detached from the structure, in case they should be re-treated, repaired or replaced. It is important to take into account this constructional challenge given the humid climate conditions of Porto and the fact that the mycelium technology is still in an experimental stage.

HOW TO GROW AN INSULATION PANEL

What is basically needed to grow a panel is a substrate to be colonized by the mycelium, a mold for the mixture to develop and grow, moisture and certain sanitary requirements so that the panel is not infected by bacteria during the process.

The substrate is usually composed by agricultural waste such as coffee, cardboard, woodchip waste, rice and wheat husks, sawdust etc., inoculated by the mycelium and let to take the shape of the mold during several days of incubation. However, since the start, it is important to use flat working surfaces, gloves and alcohol to sanitize hands and surfaces in every step of the way. Irregular surfaces or ones that can develop scratches must be avoided because they are difficult to clean and therefore promote bacteria infection.

The same goes for the mold. It should be made out of a smooth, even material, preferably transparent, so that the growth process can be observed from the outside. For this reason, one could use plastic molds and avoid wooden ones. Metal or glass molds could also be used but would need even more meticulous cleaning. The molds should be air-tight — but with a special filter or small holes in order to allow some gas exchange — and maintained with high humidity inside. They can be later used either as part of the finished panel or be removed. Alternatively, the panel can be combined with a laminated back or sandwich of a thin, rigid material when greater tensile strength is required^[6].

The length of the incubation period depends mostly on the strain, the environmental temperature and the humidity. Some fungal strains grow faster than others. For example, the oyster mushroom can grow very fast as opposed to the horse-hoof fungus (fomes fomentarius) or the trametes which grow slower. However, during a slow growth, the material is more likely to be infected and therefore demands a more specialized environment. When it comes to temperature, low temperatures will slow down the process but extremely high ones will also risk infections. Optimal growth temperature also depends on the strain, although on average it could be 25 degrees. Especially for insulation use, we should not let the mycelium grow more than necessary, as in this way the increased density of its tissue will decrease the desired porosity of the panel.

Finally, in order to terminate all biological activity and have the finished material, we have to cook the panel in a temperature between 70 and 90 degrees, preferably after pre-drying. In this process it is important to make sure that the heat inserts the core of the material. According to Maurizio Montalti, founder of Officina Corpuscoli and co-founder of Mogu, a 5 cm panel of insulation should not be cooked more than one and a half hour. Once the fungal mycelium is cured, it is not going to come alive again and the material is ready to be used.

Although still in an experimental phase, mycelium insulation can potentially replace traditional synthetic materials, such as polyurethane, reducing in that way the global environmental waste and energy consumption. However, in order to use natural systems in building construction, their benefits and constraints should first be evaluated. It is interesting to dive into the possibility of working with materials of such cultural difference than concrete, steel and plastic. Those systems refrain from the mentality of the eternal and lead us towards the concept of the ephemeral. To explore their full potential, designers will may have to face the challenge of applying and — most importantly — accepting the temporal as a building solution.

INTRODUCTION TO PROTOTYPING

The first samples processed by our Critical Change Research Lab, come from the strains of Oyster mushroom (Pleurotus Ostreatus), Shiitake and Reishi mushroom (Ganoderma Lucidum). In those samples we can see the different textures created by the mycelium depending on its type. For example the shiitake mycelium creates a much thicker, leather-like skin on the surface comparing to the oyster mushroom where the mycelium tissue appears to be less dense. We can also see how a mold-infected material looks like as well as the way in which the material gets burned when the curing temperature is higher than it should be (in this case higher than 100 degrees Celsius).

Following this article we kept working with mycelium! If you want to learn more about the possibilities that mycelium has to offer and how we produce insulation panels out of this fascinating organism, check out our ensuing articles: Insights into Mycelium (Interview with Maurizio Montalti), Producing Mycelium Insulation and Mycelium Insulation Panels!

On our YouTube-Channel you can also find a tutorial how we made the mycelium panels at the Summer School 2018.