The facades of the buildings are rarely “just” from the facades. They play an unsuspected social role in the collective imagination, between protective function, aesthetic image returned and extension of inner habitat.
In response to the first protection requirement, the building sector has developed technical innovations consisting in introducing biocides in the external layers (plaster, painting, etc.) of the walls in order to combat the development of algae, mushrooms and other foams. The key, unintentional but problematic consequences: the dissemination of these agents in the environment.
Studies in archeology have already shown that the protective layer formed by the bacterial cover (algae and mosses) on the historic monuments against the interventionist approaches which seek to eliminate them, whether by the use of biocides, or systematic cleaning.
A vast European three-year project (2019-2022), in which I participated, precisely focused on the pollution with biocides used in facades in the groundwater in the Upper Rhine region. This interdisciplinary research (ecotoxicology, hydrology, social sciences) was carried by five universities in this trinational region between Germany, France and Switzerland.
In this context, it was necessary to question the city in its socio -ecological dimension, between design of buildings (choice of coatings, professional practices, etc.) and health effects of biocidal agents.
From around forty interviews with professionals (building painters, suppliers and manufacturers of coatings), our results made it possible to assess the social acceptability of replacement products to biocides.
Indeed, these can be “intelligent” solutions based on nanoparticles or “low tech” solutions.
The responses of professionals thus oscillated between two orientations:
- A tendency to hyper technicalization that modernizes existing products (intelligent paint based on nanoparticles),
- Conversely, innovations that begin a break with the system of practices instituted and value so -called natural products (mineral paintings, use of lime).
Biocides of protective coatings, a health risk?
Biocides identified in the study are synthetic molecules used as protective films to fight against algae, mushrooms or foams. Let us quote, for example, terbutryne (algicide), daytime (herbicide) and ochtilonone (fungicide), used to prevent the development of plant species and meet a social demand for facade that remain clean.
It is interesting to note that these molecules are also used in the agricultural world and that some have been prohibited for several decades for agriculture, such as Terbutryne.
Their use in the building sector is linked to the evolution of construction techniques (for example, absence of roof overflow which protected the facades of bad weather) and to the artificialization of coatings, with the manufacture of acrylic products (oil derivatives).
The problem is that the maintenance of biocides on the facade is not sustainable. These agents are degraded under the effect of weather conditions and then washed down by the rain to spread at the foot of the facades, then in surface groundwater.
This process can be interpreted as a risk, in the sense of sociologist Ulrich Beck. Its origin is technical innovation and remains largely imperceptible. This risk has no well -defined spatial and temporal limit. These chemicals end up in underground aquifers and can impact environments far from emitting areas, especially since their effects can be deferred over time.
In addition, this risk is likely to generate a cascade of others, the consequences of which are not yet clearly identified. In particular with regard to the degradation of biocides and their interaction with other agents (from agriculture, domestic uses, etc.), the effects and dangerousness of which are still unknown.
Consequently, the biocides contained in facade paintings are a real problem for ecosystems and environmental health given their migration in groundwater under the effect of rain.
Synthetic paints against mineral
To cope with this problem in a sustainable way, it is necessary to limit the use of biocides at source or even to do without it. The professional practices of painters, at the interface between the space of professionals (suppliers, manufacturers, promoters, etc.) and that of society (inhabitants of buildings, social demand from consumers), appear as an essential link.
But the profession of building painter is not homogeneous. Like the oppositions that structure the agricultural world between conventional and biological practices, the building painters are also characterized by cleavage in the products used and their mode of application.
Our interviews show that the type of coating used (synthetic or mineral) makes it possible to establish a typology of practices which testifies to a differentiated relationship with professional identity. This takes both into account the link to bio-based materials, dependence relationships to manufacturers and suppliers and more generally the relationship to autonomy.
We can thus distinguish so -called “conventional” painters (which essentially use synthetic paintings with biocides) and the craftsmen who are moving towards more natural materials such as mineral coatings.
It should be noted that the profession must be understood as part of a whole sector where manufacturers and suppliers of coatings play a preponderant role in the definition of site operations. Indeed, manufacturers not only market coatings, but a whole set of “turnkey” recommendations.
There is often a repair coating, as well as a fixer and a finishing product. These operations channels are most often certified by the manufacturer. Their application is likely to “protect” painters from a possible dispute, in particular within the framework of the ten -year guarantee. This prescription most often becomes the standard: it is customary that painters mobilize the complete systems of the manufacturers, using the same brand for the various operating chains.
The organization of the profession in the sector thus causes a standardization of practices. Consequently, painters benefit from a limited leeway. Faced with an emerging risk like that of biocides, the profession is likely to follow the innovations offered by the networks of manufacturers-suppliers.
First alternative to biocides, “intelligent” paintings
Biocidal replacement solutions are thus part of a technical logic: industrialists develop so -called “intelligent” paintings based on nanoparticles which allow the constitution of a film to maintain dry and “clean” facades.
However, technical solutions based on the encapsulating of biocides or the use of metal nanoparticles generate new problems still little studied, such as the diffusion of microplastics or nanoparticles in the environment.
This joins the logic described by the Austrian sociologist Marina Fischer-Kowalski, specialist in social ecology, for whom our environmental problems are in particular of a “colonization” of natural processes by technique: here, the artificialization of protective coatings.
Far from questioning this movement, such technical innovations thus generate new risks.
Mineral paintings, another interesting option
A minority of professionals value the natural qualities of mineral paintings (lime, silicates) as a replacement solution to biocides. These mineral coatings have the particularity of promoting air and humidity transfers and leaving the walls “breathe”. A craftsman explained it to us:
“I do the repairs with lime -based coatings, we are completely breathable […] Because lime is a super humidity regulator and an antifungal, you cannot make it more natural ”.
This same craftsman quotes the microporosity of the coatings which helps exchanges, unlike plastic fridge:
“With mineral paintings, we have a microporosity with water vapor which is around 2000 grams per square meter. The mineral paintings are breathable, there is an exchange that is done. On semi-mineral paintings, we fall to 1200, which is not bad, so imagine with the paintings that plastic the walls ”.
The plaster has an waterproofing effect with a risk of mold. In contrast to mineral coatings which, due to their breathable properties, avoid the effects of greening. In addition to the use of mineral paintings, other alternatives emerge, such as the use of plants (in the form of essential oils) which contain bioactive molecules with antifungal properties.
These alternatives can be read as “innovations by withdrawal”. These are not based on the development of technological performance, but establish a new relationship to nature. Not only do we activate the potential of natural coatings (breathability, protection), but these become partners with whom a professional sector will be able to compose.
But these environmental innovations rest, hollow, on social innovation. Indeed, this auxiliary status comes up against brakes which testify to the difficulties in admitting that natural materials can replace synthetic and highly technical coatings.
They would however be precious for public policies aimed at initiating a transition to a city without biocide. They would re -register its functioning in natural cycles. Given biocids would indeed promote the consideration of other global issues, such as the perspective of a more permeable city, which would manage rainwater differently (Noua, sedimentation basins, etc.).
_We warmly thank Jens Lange (Albert-Ludwig University in Friborg-Allemagne) the coordinator of the Interreg Navebgo program. Research associates researchers from the Hydrology Department of Albert-Ludwig University in Friborg-en-Brisgau (Germany), the Working Group on Aquatic Functional Ecotoxicology (University of Coblence-Landau), the Institute of Sustainable Chemistry and Environmental Chemistry (University of Leuphana Lüneburg), the societies, actors, government in Europe (University of Strasbourg) that the Terre and Environment Institute of Strasbourg. _
