# Impact of the Aging Process on the Ability of Decorative Materials Containing Biocides to Support Fungal Growth

Nouha Zine Filali, Tamara Braish, Nadine Locoge, Yves Andres

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Nouha Zine Filali, Tamara Braish, Nadine Locoge, Yves Andres. Impact of the Aging Process on the Ability of Decorative Materials Containing Biocides to Support Fungal Growth. Buildings, 2024, 14 (12), pp.3859. 10.3390/buildings14123859. hal-05069417

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Article

# Impact of the Aging Process on the Ability of Decorative Materials Containing Biocides to Support Fungal Growth

Nouha Zine Filali <fnref n="1" />*, Tamara Braish <fnref n="2" />, Nadine Locoge <fnref n="2" /> and Yves Andres <fnref n="1" />

**Abstract:** Building and finishing materials are among the main sources of indoor air pollution and can provide ideal substrates for microbial growth. Environmental factors can induce physico-chemical aging of these materials, altering their composition and increasing their vulnerability to microbial growth. To mitigate this risk, manufacturers are increasingly adding biocidal agents to these materials to prevent microbial contamination. The aim of this project was to study the sensitivity of two different acrylic paints to fungal growth, before and after an aging process, and to assess the impact of aging on the effectiveness of the biocides contained in these materials. To do this, two paints (antifungal and normal paint) were applied to a wall covering (polyester-cellulose) before being subjected to accelerated aging. The later process was based on the addition of detergent or water and exposing the material to a visible light spectrum, moderate temperature (38 ± 6 °C), and ambient relative humidity (25 ± 17%). Prior to 30 days of incubation, the aged and unaged ("native") materials were inoculated with fungal spores using a dry aerosolization system. Fungi behavior was then evaluated by the culture method. The results showed that the native and water-aged normal acrylic paint supported fungal growth at 95 ± 5% relative humidity. However, the use of the cleaning product during the aging process provided additional resistance of the materials against fungal growth. On the other hand, the antifungal paint showed no visible growth due to its biocide content. The accelerated aging and incubation processes led to the depletion of the biocides and thus a decrease in their effectiveness against mold development.

**Keywords:** antifungal treatments; mold growth; aging process; acrylic paint; aerosolization; indoor air quality

## 1. Introduction

People in industrialized countries spend 70-90% of their time in confined spaces (homes, offices, transportation vehicles, or public places), where they are generally exposed to high concentrations of indoor air pollutants over a long period of time [1-3].

As a consequence, exposure to poor Indoor Air Quality (IAQ) can lead to ailments including asthma, throat irritation, shortness of breath, and heart disease. It can also lead to chronic lung disease, bronchitis, and cancer [4]. It has been estimated that up to 20% of people living in European and North American homes were affected by the presence of visible mold [5]. Along with this, it is estimated that in 2014 in the United States, more than 4.5 million cases of asthma resulted from exposure to moisture and mold, with an annual economic cost of approximately USD 3.5 billion [6].

Microbial contaminants in indoor environments include a variety of bacteria (e.g., *Staphylococcus* spp., *Pseudomonas* spp., and *Bacillus* spp.), viruses (such as influenza virus and SARS-CoV-2 virus), fungi, and actinomycetes, which are generally brought into enclosed spaces by occupants and natural or mechanical ventilation systems [7-9]. Fungal

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**Citation:** Zine Filali, N.; Braish, T.; Locoge, N.; Andres, Y. Impact of the Aging Process on the Ability of Decorative Materials Containing Biocides to Support Fungal Growth. *Buildings* **2024**, *14*, 3859. https://doi.org/10.3390/buildings14123859

Academic Editor: Ricardo M. S. F. Almeida

Received: 18 October 2024

Revised: 20 November 2024

Accepted: 27 November 2024

Published: 30 November 2024

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**Copyright:** © 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

<footnote n="1">¹ Laboratoire de Génie des Procédés Environnement Agro-Alimentaire (UMR CNRS 6144), Institut Mines Télécom Atlantique, 44300 Nantes, France; yves.andres@imt-atlantique.fr</footnote>

<footnote n="2">² Centre for Energy and Environment, Institut Mines Télécom Nord Europe, University of Lille, F-59000 Lille, France; tamara.braish@imt-nord-europe.fr (T.B.); nadine.locoge@imt-nord-europe.fr (N.L.)</footnote>

<footnote>* Correspondence: nouha.zine-filali@imt-atlantique.fr; Tel.: +33-2-51-85-82-86</footnote>
species, in particular, are frequently transported into buildings by clothing, footwear, and ventilation systems. Their widespread distribution is facilitated by the production and airborne transmission of fungal spores, which contribute to their accumulation in dust and colonization of building surfaces such as walls, partitions, and ceilings. The most common environmental molds isolated from contaminated materials are *Acremonium* spp., *Alternaria* spp., *Aspergillus* spp., *Chaetomium* spp., *Cladosporium* spp., *Epicoccum* spp., *Fusarium* spp., *Penicillium* spp., *Stachybotrys* spp., and *Trichoderma* spp. [10,11].

Microbial growth is strongly influenced by climatic conditions, including high relative humidity (greater than 75%), moderate temperature (20–29 °C), and nutrient availability [12]. These conditions are considered the key factors for the alteration of any type of material [12,13]. However, the nature, porosity, and density of the substrate can also have an important impact on the susceptibility of the material to microbial growth [14]. Once the material is contaminated, it is considered an important reservoir of microorganisms from which fungal spores can spread into indoor air and then settle on other surfaces. In addition, the exposure of building and furnishing materials to certain environmental conditions (temperature, light, relative humidity, ozone, etc.) can lead to an acceleration of their physico-chemical degradation, resulting in the embrittlement of the material and the release of biodegradable by-products, which promote microbial growth [15]. As an example, the predominant degradation pathway of the polyester molecule under different accelerated aging conditions (acid or wet alkaline) is the hydrolysis of the ester bonds and the autocatalysis with potential synergistic photooxidation (in the presence of oxygen and light or with temperature). This leads to the reduction of the degree of polymerization and the formation of low molecular weight by-products, including aliphatic organic acids and Volatile Organic Compounds (VOCs), which are easily assimilated by molds [15–17].

Microorganisms can affect the material in damp indoor conditions in two forms:

(i) Physical: through the creation of cracks (hyphae production), swelling, and delamination of the surface and (ii) Chemical: through the production of stains (pigment synthesis) and the synthesis of a series of enzymes and chemical substances to establish a process of assimilation and dissimilation of the material's constituents [18,19].

In addition, they may also affect the occupants' health by producing metabolites and waste products (microbial VOCs, mycotoxins, and CO₂) [5,20,21]. In this context, the World Health Organization has published IAQ guidelines to prevent moisture and mold-related problems [22].

Therefore, to reduce the risk of microbial proliferation, two main strategies have emerged. On the one hand, occupants are increasingly using surface cleaning products such as disinfectants, floor cleaners, and multi-surface sprays. This trend has become particularly pronounced since the COVID-19 pandemic, triggered by the spread of SARS-CoV-2 starting in December 2019 [23–27]. For example, a study by Gharpure et al. [28] revealed that 33% of Americans used household disinfectants more frequently and more dangerously to address microbiological risks, including those linked to SARS-CoV-2. Similarly, research by Vayisoglu and Oncu indicates a significant increase in the frequency of cleaning and the use of cleaning products in Turkey over the last four years, increasing by 69% and 74%, respectively, compared to earlier levels [27]. In France, a significant increase in exposure to household cleaning products, including biocides and alcohol-based disinfectants, was also observed [29]. While these cleaning practices are essential for hygiene and disease prevention, they can also lead to potentially harmful exposure to primary and secondary indoor pollutants due to emissions from cleaning products and their interactions with other airborne compounds [30–33]. In addition, the frequent use of cleaning products can have an impact on the cleaned materials, promoting premature aging and altering the composition and properties of surfaces over time [34–37].

On the other hand, the inclusion of biocides in building materials has also been increasingly adopted by manufacturers and controlled by the European Union (EU) [38,39], with the aim of preventing, protecting, and preserving the material during storage or service life. In particular, they are used as preservatives in paints and coatings based on aqueous
polymer resins. The biocides most commonly used in these materials are isothiazol-3-ones, phenylureas, carbamates, and triazines [40–42]. Preservatives commonly used in canned products include 2-methylisothiazol-3(2 H)-one (MIT), 5-chloro-2-methylisothiazol-3(2 H)-one (CMIT), and benzo[d]isothiazol-3(2 H)-one (BIT). For the protection of final coating films applied to interior and exterior walls, biocides such as 2-octylisothiazol-3(2 H)-one (OIT) and 4,5-dichloro-2-octylisothiazol-3(2 H)-one (DCOIT) are frequently used. However, the lifespan of these biocides can also be affected by environmental conditions such as sunlight, temperature, pH, and water contact [43–46]. Several monitoring studies showed that biocides are leached from the material’s surface once it comes into contact with rainwater and end up in the environment via runoff [47–50]. Ultraviolet (UV = 254 nm) radiation from sunlight has been identified to cause the photodegradation of certain biocidal compounds, including OIT and BIT, thereby reducing their efficacy over time [45,51]. Temperature fluctuations, such as daily heating and cooling cycles, can further accelerate the chemical reactions that degrade biocides. For instance, the half-life of DCOIT declines significantly with increasing temperatures from 64 days at 4 °C to just 4.5 days at 40 °C [52]. Similarly, pH variation from acidic (pH < 7) to basic (pH > 7) contributes to the degradation process, highlighting the vulnerability of biocides under variable environmental conditions [51–54].

Despite the widespread use of biocides, research into their persistence, degradation, and efficacy over time under various indoor environmental conditions remains limited [42]. This study aims to investigate the influence of aging on biocide efficacy and material durability under controlled laboratory conditions that faithfully reproduce real-world environments. Accelerated aging was carried out over 30 days, using lamps emitting visible light spectra (400–450 nm to 600–650 nm) to simulate prolonged exposure to sunlight through windows. Simultaneously, the chamber temperature was raised to 38 ± 6 °C under the effect of the lamps, mimicking the daily thermal expansion and contraction of the materials. In a subsequent phase, the materials were subjected to fungal inoculation by aerosolization for 45 min, followed by incubation under conditions of high relative humidity (95 ± 5%) and stable temperatures (23 ± 1 °C) for 30 days in the dark. These parameters were designed to reproduce extreme water exposure conditions conducive to fungal growth.

This study provides valuable insights for the development of more sustainable and environmentally friendly biocide treatments, improving both the performance and longevity of protective materials.

## 2. Materials and Methods

### 2.1. *Building and Decorative Materials*

The materials in this study were selected based on their potential biodegradability and the content of antifungal substances in at least one of the used products.

The used materials were commercially purchased and include the following:

- Polyester Cellulose (PEC): Smooth renovation wall covering containing polyester and cellulose. It is used in this study as a support for decorative materials and as a positive control for fungal growth.

- Antifungal paint (AFP): Suitable for all interior surfaces thanks to its moisture resistance and mold prevention. It contains acrylic resin, titanium pigment, and iron oxide. Biocides include 2,4,7,9-tetramethyldec-5-yne-4,7-diol (TMetdediol), 3-iodo-2-propynyl butylcarbamate (IPBC), and 1,2-benzisothiazol-3(2H)-one (BIT), whose concentrations are not provided by the manufacturer.

- Normal Acrylic paint (AP): Suitable for damp surfaces. It is resistant to water and temperature variations. It contains the following biocides: 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-2H-isothiazol-3-one (3:1) (CMIT/MIT) as well as 1,2-benzothiazol-3(2H)-one (BIT), which are labeled as preservatives for liquid paint storage.
## 2.2. Methodology

To maintain conditions close to reality and meet the study's objectives, a specific protocol has been established, as detailed below (Figure 1):

<figure><img src="image_5.png" /><figcaption>**Figure 1.** Experimental approach used to assess the effect of aging on combined materials (antifungal and normal acrylic paints applied to a polyester-cellulose wallcovering) and their biocidal content.</figcaption></figure>
Two different paints (antifungal and normal paint) were applied separately to a wall covering (polyester-cellulose) and cut into 18 samples. Nine samples were subjected to various accelerated aging conditions, while the remaining nine were left untreated and will be referred to as “native” in the remainder of this document.

The eighteen samples (native and aged) were distributed as follows:

- Six samples (3 native and 3 aged) were used for biocide Emission Rate (ER) measurements to examine the differences in emissions between native and aged samples.

- Twelve samples were subjected to fungal inoculation by dry aerosolization and divided as follows: six samples (3 native and 3 aged) were tested for biocide ER. These measurements are intended to assess the effects of high-humidity incubation and possible fungal growth on the material. The remaining six inoculated samples (3 native and 3 aged) were subjected to quantitative measurements of fungal concentration, expressed in CFU cm⁻².

The aging process consisted of 30 days of accelerated physico-chemical aging, divided into four stages:

The initial step involves exposing the material to a combination of physico-chemical aging factors, in particular exposure to light and the application of a cleaning agent. If fungal growth is observed on both types of material (native and aged), the material will be classified as biodegradable and free of biocidal effects, and the test will end at this stage. If aging promotes the growth of inoculated spores, this will be considered sufficient to alter the biocide, enabling the functional life of biocides to be estimated.

Conversely, if aging reveals fungal inhibition, i.e., a significantly lower concentration of inoculated spores on aged materials than on native samples, a second step will be implemented. This involves dividing the aging factors, first by exposing three additional samples to light alone, then three more to the combined effect of light and water. If fungal growth remains absent, whether on the aged material alone or on both types of material (native and aged), a third and final step will be implemented. This step consists of adding a nutrient solution designed to fulfil two functions: to facilitate the diffusion of the biocide (if it is present) from the material into the solution and, in the event of nutrient deficiency, to act as a nutrient medium to promote fungal proliferation.

### 2.2.1. Sample Preparation

The polyester-cellulose support was cut into a group of circular samples with a surface area of approximately 64 cm² each. A total of 48 samples were covered by an antifungal paint layer (0.49 ± 0.025 g), 12 other samples were covered by a layer of the normal acrylic paint (0.50 ± 0.017 g), and 9 other samples were kept uncovered to use as a positive control for the inoculation process.

The 48 samples coated with antifungal paint were divided into 4 series:

- Twelve (3 native, 3 aged, and 6 inoculated incubated native and aged) samples were used to evaluate the biocide ER;

- Twelve (3 native and 9 aged) samples were used to evaluate the ability of the material to promote fungal growth after 30 days of incubation under high relative humidity (95 ± 5%);

- Eighteen samples were designated to monitor the growth/survival of deposited spores on the native materials during the 30 days of incubation by evaluating the fungal growth on 3 samples out of the 18 every 7 days. The significant difference between the concentration of initially inoculated spores on the first day (D0) and those on the other sampling days was calculated using a nonparametric Kruskal-Wallis test with an alpha risk of 0.05%, followed by Dunn's correction;

- Six (3 native and 3 aged) samples on which 8 mL of a nutrient solution (10 g L⁻¹ Tryptone—5 g L⁻¹ Meat extract—5 g L⁻¹ Sodium chloride) was added to evaluate the depletion of biocides over time (before and after the aging process).
The twelve samples coated with the normal acrylic paint were divided into 6 (3 native and 3 aged) samples to evaluate the ability of the material to promote fungal growth and 6 other samples (3 native and 3 aged) to which 8 mL of the nutrient solution was added to similarly assess biocide depletion over time.

### 2.2.2. Material Aging

The aging process consisted of a 30-day physico-chemical procedure conducted in a sealed chamber (Figure 2). The chamber was equipped with two lamps providing ambient heating at T = 38 ± 6 °C and maintained an ambient relative humidity (RH) = 25 ± 17%. This process was divided into three scenarios:

(1) "Cleaning Product and Light Aging Process" (CPLAP): This involved adding a commercial cleaning product, with the aim of reproducing real-life conditions and daily cleaning habits. The composition of the cleaning product, used during the aging process, was determined by spiking 1 µL of this product into a Tenax TA adsorbent tube and then analyzing it by TD-GC-MS/FID. During the aging process, 869 ± 61 µL of this detergent was sprayed twice a day for one month onto the aging samples. After a 5 min application, the detergent was wiped off with a paper towel to simulate typical occupant cleaning habits and accelerate the aging process. The material was also continuously exposed to a visible light spectrum (400–450 nm to 600–650 nm) for 30 days. The distance between the light and the samples was equal to 48 cm (Figure 2).

(2) "Water and Light Aging Process" (W LAP): This test is similar to the previous one, except 803 ± 132 µL of ultra-pure water, instead of the cleaning product, was sprayed twice a day for one month on the surface of the material.

(3) "Light Aging Process" (LAP): This consisted only of continuous exposure of the samples to the visible light spectrum for 30 days.

<figure><img src="image_6.png" /><figcaption>**Figure 2.** Aging chamber.</figcaption></figure>

The purpose of the second and third aging processes is to study the individual impact of each aging parameter (the use of detergent and the application of light) on the depletion of biocides and thus the susceptibility of the material to fungal growth.

### 2.2.3. Fungal Inoculation

Several preliminary tests, including impaction sampling of bioaerosols using the MAS-100NT air sampler (MBV AG, Stäfa, Switzerland) with a 1000 L/10 min sampling system, as well as cultivation on various synthetic solid media (nutrient agar, malt extract agar, and Reasoner 2A agar), were performed to select a suitable environmental fungus for cultivation on PEC. These tests showed that *Aspegillus niger* and *Pencillium* sp. have the ability to successfully grow on PEC, regardless of inoculation and incubation conditions.

*Cladosporium sphaerospermum*, known to grow on both cellulose and acrylic paint [18,55,56] and to withstand extreme conditions [57], was selected from the culture collection (DSM 104746, Leibniz Institute DSMZ, Braunschweig, Germany) to be used with *Aspegillus niger* and *Pencillium* sp. as a material inoculant.
Fungal inoculation was performed by dry aerosolization, using 15 min of air pumping (D = 10 L min⁻¹), carrying the fungal spores into a sealed chamber (V = 103 L). The sealed chamber contained the different samples (native, aged, covered, and uncovered) in addition to 8 sterile empty Petri dishes (for the quantification of the inoculated spores’ concentration) placed randomly in the sealed chamber (Figure 3). Fungal contamination took place by the sedimentation of the airborne spores for approximately 45 min.

<figure><img src="image_7.png" /><figcaption>Figure 3. Inoculation of samples with fungal spores.</figcaption></figure>

The incubation of the inoculated samples was performed over 30 days under appropriate relative humidity (95 ± 5%) for fungal growth and moderate temperature (23 ± 1 °C).

### 2.2.4. Fungal Growth Assessment

The quantification of the developed fungi on the surface of the material was carried out in two steps:

The first step ($T_0$) was to quantify the initial concentration of inoculated spores. This step was performed just after the sedimentation period. It consisted of recovering the settled spores from the empty Petri dishes with 10 mL of isotonic solution ($10^{-2}$ M MgSO₄ and 0.25% Tween 20). The spore recovery was followed by a series of 1/10th dilutions, of which 0.1 mL was taken from each dilution and spread on a Dicloran Rose-Bengal Chloramphenicol (DRBC) agar medium (Biokar Diagnostics, Pantin, France), to finally obtain the fungal concentration in CFU cm⁻² after incubation at 25 ± 2 °C for 3 days, by applying the following equation:

$$ \text{Concentration (CFU cm}^{-2}\text{)} = \frac{\text{number of detected colonies (CFU)} \times \text{dilution factor}}{\text{surface area of material (cm}^{2}\text{)}} $$

The second step ($T_{+30d}$) was to evaluate the fungal growth on the inoculated surface of each tested sample after 30 days of incubation. This step was first performed by visual inspection followed by a quantitative evaluation that included, as previously described, counting the concentration of developed molds. The Limit Of Detection (LOD) of fungal quantification was equal to 2 CFU cm⁻².

The inoculation and incubation processes and the assessment of fungal growth are identical to those used by [58,59].

### 2.2.5. Variation in Biocide Emission Rates from Acrylic Paints After Aging and Incubation Process

The assessment of biocide content, likely to have an antifungal effect on the native acrylic dry paint, and the assessment of the aging impact (“aged materials”) and the combined effect of the aging and incubation processes (“aged and incubated materials”) on its depletion over time were performed by semi-quantitative Thermodesorber/Gas Chromatography—Mass Spectrometry/Ionizing Flame Detector (TD-GC-MS/FID) analysis.
This test was performed according to the French label [60] and is similar to that used in previous studies [59,61]. The LOD of the GC method was equal to 0.004 µg m⁻³.

### 2.2.6. Paint Characterization

To accurately determine the carbon, hydrogen, oxygen, sulfur, and nitrogen content of the two used paints, elemental analysis was performed using a Thermo Electron Flash EA 1112 analyzer (Thermo Fisher Scientific, Waltham, MA, USA). This analyzer has an LOD of 0.06% and a Limit Of Quantification (LOQ) of 0.2% for each element. Triplicate measurements were conducted for each sample to ensure repeatability, with sample weights ranging from 0.5 to 1 mg, enabling the quantification of the elemental composition (C, H, N, S, and O) in the paints.

Additionally, Energy-Dispersive X-ray spectroscopy (EDX) analysis was also performed using the EDX-720/800HS/900HS (Shimadzu Europe, Duisburg, Germany) instrument to perform the qualitative and quantitative analysis of trace elements that could support fungal growth. The LOD of EDX analysis is 0.001%.

## 3. Results and Discussion

### 3.1. Material Characterizations

Fungi, like other organisms, have a number of nutritional requirements to ensure various vital functions. They require a source of carbon substrates to provide sufficient energy for cell growth and also to act as carbon sources for new cell synthesis. In addition, they need inorganic sources (ammonium, nitrate, or phosphate ions) and traces of other minerals (calcium, potassium, magnesium, and iron) for the biosynthesis of essential constituent molecules, such as amino acids, proteins, nucleic acids, glucosamine, and chitin [12].

In an ambient environment, fungi adapt to uptake nutrients and substrates from their surroundings. Simple soluble nutrients are absorbed through the cell wall and plasma membrane, but the substrate is often composed of long complex polymers that need to be broken down by specific enzymes secreted by the fungi. In this part of the study, elemental analysis and EDX were performed to obtain a rough indication of the composition of the materials and the potential sources that could be used for fungal growth. Table 1 shows some detected elements in three material types (polyester cellulose and acrylic and antifungal paints).

<table><caption>**Table 1.** Analysis of the composition of the used polyester cellulose and the two acrylic paints. The standard deviation represents three measurements.</caption><thead><tr><th>Compounds/Materials</th><th>Polyester-Cellulose</th><th>Acrylic Paint</th><th>Antifungal Paint</th></tr></thead><tbody><tr><td>N (wt.%)<sup>1</sup></td><td>&lt;LOQ<sup>2</sup></td><td>0.6 ± 0.01</td><td>0.4 ± 0.09</td></tr><tr><td>C (wt.%)</td><td>45 ± 0.06</td><td>35 ± 0.05</td><td>31 ± 0.002</td></tr><tr><td>H (wt.%)</td><td>5 ± 0.05</td><td>5 ± 0.02</td><td>4 ± 0.04</td></tr><tr><td>S (wt.%)</td><td>&lt;LOD</td><td>&lt;LOD<sup>3</sup></td><td>&lt;LOD</td></tr><tr><td>O (wt.%) (by the difference)</td><td>40 ± 0.3</td><td>15 ± 0.03</td><td>7 ± 0.17</td></tr><tr><td>Ti (wt.%)</td><td>0.5 ± 0.4</td><td>40 ± 0.04</td><td>33 ± 0.2</td></tr><tr><td>Ca (wt.%)</td><td>0.9 ± 0.4</td><td>0.1 ± 0.04</td><td>22 ± 0.2</td></tr><tr><td>Mg (wt.%)</td><td>&lt;LOD</td><td>0.6 ± 0.04</td><td>&lt;LOD</td></tr><tr><td>P (wt.%)</td><td>0.6 ± 0.4</td><td>0.3 ± 0.04</td><td>0.3 ± 0.2</td></tr><tr><td>Zn (wt.%)</td><td>&lt;LOD</td><td>&lt;LOD</td><td>0.1 ± 0.2</td></tr><tr><td>Fe (wt.%)</td><td>0.3 ± 0.4</td><td>0.2 ± 0.04</td><td>0.1 ± 0.2</td></tr><tr><td>Moisture (wt.%)</td><td>2 ± 0.5</td><td>46 ± 0.03</td><td>52 ± 1.2</td></tr><tr><td>Ash (wt.%)</td><td>9 ± 0.4</td><td>45 ± 0.04</td><td>57 ± 0.2</td></tr></tbody></table>

Based on the results presented in Table 1, the majority of the detected elements show a similar proportion for the three materials, except for titanium, which shows a low

<footnote n="1">¹ (wt.%): percentage of weight; ² LOQ: limit of quantification; ³ LOD: limit of detection.</footnote>
proportion (0.5 ± 0.4%) for PEC, and calcium, which shows a higher proportion (22 ± 0.2%) for the antifungal paint compared to the acrylic paint (0.1 ± 0.04%) and PEC (0.9 ± 0.4%).

It is also noted that oxygen content was higher in PEC (40 ± 0.3%), referring to the presence of oxygenated compounds that are more easily assimilated by molds. The water content was higher in both types of paint compared to PEC (2 ± 0.5) due to the presence of solvents in the paint composition.

The minimum nutrient requirements for fungi (determined in liquid culture medium, as agar contains impurities that can bias results) are approximately 2% carbon, 0.2% nitrogen, 0.1% potassium and phosphorus, 0.05% magnesium, 0.005% calcium, and 0.005% chlorine sources [12]. The comparison of these values with those obtained in our study leads us to believe that the analyzed materials contain sufficient elements to support fungal growth under certain environmental conditions [62,63].

Cellulose, for instance, is a polymer assimilated as a single source of substrates by *Aspergillus niger*, *Penicillum notatum*, and *Cladosporium* sp. when environmental conditions (pH, temperature, moisture, level of antifungal substances, etc.) are met [56,63]. Moisture bioavailability is found to be a crucial element for fungal growth [57]. An analysis by Reis-Menezes et al. [56] on the biodegradation of different types of cellulose (book paper) under two different humidity conditions (95–100%) revealed that the higher the relative humidity, the greater the fungal growth. In their study, they also showed that the addition of calcium carbonate on paper led to better fungal growth. This reveals that the high concentration of calcium (22 ± 0.2%) found in the antifungal paint could promote the growth of inoculated fungi.

Titanium dioxide (TiO₂), on the other hand, is responsible for the white color, brightness, and durability of building materials and is a widely used pigment in wall coatings. It is responsible for maintaining quality for a longer period of time due to its very high light refraction and heat resistance [64].

## 3.2. Biodegradability of Decorative Materials Under Different Aging Conditions

### 3.2.1. Antifungal Paint (AFP)

In order to study the ability of AFP to support fungal growth, a dry inoculation of fungal spores by an aerosolization system, without providing any kind of nutrient, was performed on AFP in its different states (native, WLAP, CPLAP, or LAP) and on native PEC, serving as a positive control. The results of the AFP resistance to fungal growth are presented in Figure 4.

<figure><img src="image_8.png" /><figcaption>**Figure 4.** Concentration variation (CFU cm⁻²) of inoculated spores on uncovered material (PEC) and on combined antifungal paint (AFP) in different states: Native, Light Aging Process (LAP), Cleaning Product and Light Aging Process (CPLAP), and Water and Light Aging Process (WLAB) after 4 weeks of incubation. The y axis is scaled to Log10. Error bars represent standard errors of 3 measurements.</figcaption></figure>
According to Figure 4, the concentration of inoculated spores was equal to (3 ± 4) × 10² CFU cm⁻². After 30 days of incubation, only the native PEC showed fungal growth with a concentration of (2 ± 1) × 10⁶ CFU cm⁻². However, none of the native or aged AFP showed visible signs of growth. Furthermore, the concentration of spores on the AFP surface was below the detection limit (<LOD), revealing that no viable inoculated spores were recovered on the AFP surface after incubation. This result suggests that the inoculated spores were not able to survive on the antifungal paint surface (native or aged). Thus, the aging process used in this study did not have a positive effect on mold growth.

Three assumptions can be proposed to explain the non-resistance of the inoculated spores on the different antifungal paint surfaces: (i) the high applied relative humidity (95 ± 5%) during the incubation process might have enabled the germination of the fungal spores, but these germinated spores could not survive for a long time because of the low nutrient availability from the polymerized paint; (ii) the biocides emitted by the antifungal paint could have a negative effect on mold growth; (iii) the hydrophobicity of the material did not allow water uptake from the ambient environment.

Vacher et al. reported in their study that adding thin wallpaper (80 g) or acrylic paint as a cover to biocide-free plasterboard supports fungal growth, especially *Aspergillus niger* and *Penicillium* sp. In contrast, the addition of wallpaper to biocide-treated plasterboard (2.5% of 1,2-benziothiazol-3-(2H)-one and 2.5% of 2-methyl-4-isothiazol-2-one) prevents fungal growth by transferring some of the biocides to the wallpaper. For acrylic paint applied to biocide-treated gypsum board, slow fungal growth was noted [14]. These results showed that the biodegradable support behaves differently toward fungal growth depending on the nature of the coating applied to it.

To further investigate fungal death on the surface of the antifungal paint, a survival kinetic was performed during the 30 days of incubation by taking three samples every 7 days from the first day of inoculation to the 30th day of incubation. As illustrated in Figure 5, on the first day of inoculation (D₀), (1.6 ± 1) × 10³ spores per cm² were inoculated on the surface of the native antifungal paint; then, after 7 days of incubation, this concentration decreased to 24 ± 20 spores per cm², and then to 7 ± 1 spores per cm² after 14 days of incubation, until exhaustion after 21 days of incubation. These results show that during the incubation period, the spores respond to the environmental stimuli (water, oxygen, and the availability of a fermentable substrate such as glycerol or acetate) and lose their resistance by triggering the germination process during the first 6–8 h [65,66]. Then, due to the insufficient nutrients or because of the presence of biocides initially contained in the material, they are not able to survive for long on the surface of the material.

<figure><img src="image_9.png" /></figure>

**Figure 5.** Representation of the survival of inoculated spores on native antifungal paint (CFU cm⁻²), starting from the first day of inoculation (D₀) to the last day of incubation (D₃₀). The y axis is scaled to Log10. Error bars represent standard errors of 6 measurements. Significance was calculated with respect to deposited spores using a nonparametric Kruskal–Wallis test, with an alpha risk of 0.05%, followed by a Dunn's correction to analyze the different samples. **: *p* < 0.005 and ***: *p* < 0.0005.
### 3.2.2. Acrylic Paint (AP)

In order to investigate whether the nature of the acrylic polymer is responsible for the low nutrient availability, high hydrophobic surface area, and fungal mortality, a fungal inoculation and quantitative assessment of fungal growth on the normal acrylic paint was performed (Figure 6).

<figure><img src="image_10.png" /><figcaption>**Figure 6.** Concentration variation (CFU cm⁻²) of inoculated spores on uncovered material (PEC) and on combined acrylic paint (AP) in different states: Native, Light Aging Process (LAP), Water and Light Aging Process (W LAP), and Cleaning Product and Light Aging Process (CPLAP) after 4 weeks of incubation. The y axis is scaled to Log10. Error bars represent standard errors of 3 measurements.</figcaption></figure>

According to Figure 6, the native PEC shows fungal growth with a concentration of (2 ± 1) × 10⁶ CFU cm⁻², which is 10⁴ times higher than the inoculated spores ((2.5 ± 3) × 10² CFU cm⁻²). The same is true for the native AP, where fungal growth was observed with a concentration of (5 ± 5) × 10⁵ CFU cm⁻², which is 10³ times higher than the initially inoculated spore concentration. This suggests that the acrylic paint supports the fungal growth and that the present biocides (5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-2H-isothiazol-3-one (3:1) and 1,2-benzothiazol-3(2H)-one) used as preservatives did not negatively impact the fungal growth. For the aged materials, only the WLAP material showed a fungal growth ((2 ± 0.7) × 10⁷ CFU cm⁻²), which is more than 10⁵ times higher than the initially inoculated spores, whereas the CPLAP showed no signs of fungal growth.

From these results, it can be concluded that the cleaning product used during the aging process has an adverse impact on the viability of the inoculated spores. However, the water used during the aging process led to the embrittlement of the material and, therefore, to an increase in the fungal concentration by a factor of 100 compared to the native AP, revealing that this type of aging promotes the accessibility to fungi.

Considering the percentage of water absorption after WLAP, where AP shows 10 ± 4% and AFP is 6 ± 2%, the following conclusions can be drawn.

In terms of hydrophobicity, both antifungal (AFP) and normal (AP) acrylic paints can be classified as moderately hydrophilic, as they demonstrate a significant capacity (>5%) to retain water. In terms of biodegradability, standard acrylic paint promotes fungal growth despite the presence of biocides serving as preservatives for canned products. Antifungal paint, on the other hand, effectively inhibits mold growth on PEC.

Regarding the aging process, the use of water during this process favors alteration of the AP and consequently promotes fungal growth, while aging using a cleaning product is responsible for the antifungal action. The latter can be explained by the following two hypotheses: (i) biocides present in the acrylic paint were transferred to the material surface
through the use of the cleaning agent, resulting in the death of the initially deposited spores; (ii) the used cleaning agent contains fungicidal compounds that induced the death of the germinated cells.

To identify the potential effect of the cleaning product on the fungal growth, an agar diffusion test was performed. It consisted of spreading an *A. niger* spores onto a DRBC agar plate and then placing detergent-soaked and dried paper discs on the top, which were then incubated at 25 °C for three days. During the incubation period, the *A. niger* strain grew rapidly on the DRBC medium, while the detergent discs affected fungal growth by creating an inhibition zone around each disc (Figure 7). These results support the second hypothesis that the detergent has a fungicidal effect and is therefore responsible for the death of inoculated spores on the aged samples (Figure 6).

<figure><img src="image_11.png" /><figcaption>**Figure 7.** Impact of the cleaning product on *A. niger* growth.</figcaption></figure>

Indeed, TD-GC-MS/FID analysis showed that the detergent is composed of about 27 compounds, mainly alcohols (33%), hydrocarbons (30%), aldehydes (19%), a small fraction of terpenes (Limonene and α- and β-pinenes) (11%), and organic acids (7%). Table 2 shows an extract of the mass concentrations (Cm) of certain detergent compounds known to influence fungal growth.

<table><caption>**Table 2.** The mass concentration (Cm, µg mL⁻¹) of the detected compounds in the used cleaning product.</caption><thead><tr><td>Compounds</td><td>Cm (µg mL<sup>-1</sup>)</td></tr></thead><tbody><tr><td>D-Limonene</td><td>15</td></tr><tr><td>β-Pinene</td><td>2.5</td></tr><tr><td>1-Octanol</td><td>32</td></tr><tr><td>1R-α-Pinene</td><td>1</td></tr><tr><td>P-Mentha-1,5-Dien-8-Ol</td><td>5</td></tr><tr><td>1-Decanol</td><td>37</td></tr><tr><td>2,6-Dimethyl-2,6-Octadiene-1,8-Diol</td><td>4</td></tr><tr><td>1-Dodecanol</td><td>462</td></tr><tr><td>1 Hexadecanol/1-Tetradecanol</td><td>143</td></tr><tr><td>Decanol</td><td>44</td></tr></tbody></table>

Alcohols are widely used for inert surface disinfection, hand hygiene, and at lower concentrations as preservatives. They have broad-spectrum, fast-acting antimicrobial activity. The aging process, however, can lead to the evaporation of most alcohols present in the applied cleaning product.

Terpenes (limonene, α and β-pinenes) are also commonly used for surface disinfection, as preservatives, and in the pharmaceutical industry due to their broad antibacterial, antifungal, and anti-insect potential [67]. The mode of action of these compounds is believed to interact with membrane cells due to their lipophilic nature, leading to the inhibition of membrane enzymes and increasing the fluidity of cell membranes. They can
also affect the respiration by inducing the accumulation of reactive oxygen species (ROS) and the ionic transport of microorganisms [68–70]. It has been shown that α-pinene has an antifungal effect, especially against *A. niger* and *Penicillium* sp. [71]. However, β-pinene is more effective against other fungi such as *Fusarium* sp. [72].

### 3.3. *Variation in Biocide Emission Rates from Antifungal Paints After Aging and Incubation Process*

In order to assess the contribution of biocides to the fungal resistance, measurement of the biocides released from the antifungal paint at the different states (native, inoculated incubated, CPAP, and combined incubation cleaning-product aging processes) was performed using the semi-quantitative TD-GC-MS/FID method (Figure 8). The assay consisted of characterizing the emissions of two samples from the three prepared replicates at each state. Only one biocide (2,4,7,9-tetramethyldec-5-yne-4,7-diol) was detected using this method. The analysis of biocide emissions from normal acrylic paint was not carried out, as the biocides used were intended to protect the material in its liquid state.

<figure><img src="image_12.png" /></figure>

**Figure 8.** Evolution detected biocide, 2,4,7,9-tetramethyldec-5-yne-4,7-diol (TMetdediol), emission rate (µg m⁻² h⁻¹) from the antifungal paint (AFP) in the different states (incubation, aging with cleaning product, and combined incubation cleaning-product aging processes). Error bars represent standard errors of 3 measurements.

According to Figure 8, the native emission rate of 2,4,7,9-tetramethyldec-5-yne-4,7-diol was 29 ± 5 µg m⁻² h⁻¹, which then dropped to 10 ± 2 µg m⁻² h⁻¹ for inoculated incubated native materials. For the aged materials, the ER dropped further to 2 ± 0.2 µg m⁻² h⁻¹, finally stabilizing at 2 ± 0.8 µg m⁻² h⁻¹ for inoculated and incubated aged materials. These results are consistent with those of a previous study on OIT and MI biocide emissions from plaster in different states (native, native inoculated and incubated, aged, and aged inoculated and incubated). In this study, the native ERs of MIT were 1.97 and 2.10 µg m⁻² h⁻¹ for the first and second samples, respectively. Subsequently, the ER dropped below the detection limit after inoculation, aging, and the combined processes of aging and inoculation. Similarly, OIT showed a native ER of 2.71 and 2.94 µg m⁻² h⁻¹ for the first and second samples, respectively. These rates dropped to 0.55 and 0.62 µg m⁻² h⁻¹ for the first and second inoculated and incubated samples, respectively, and became undetectable in all other samples [59].
These results demonstrate a significant decrease in the biocide's emission rates to very low levels, and even exhaustion for some species despite the difference in the nature of the materials and the type of biocide measured. Indeed, during the incubation period, and due to the high applied relative humidity (95 ± 5%), the materials absorbed water from the surrounding environment. For AFP, water absorption was approximately 0.15 ± 0.06 g and 0.7 ± 0.2 g in the native and aged state, respectively, which constitutes 10 ± 4% and 48 ± 14% of the acquired mass in the native and aged state, respectively. For AP, the water absorption was 0.2 ± 0.1 g and 0.8 ± 0.4 g in the native and aged state, respectively, representing 14 ± 4% and 51 ± 18% of the acquired mass in the native and aged state, respectively. The absorbed water diffuses into the bulk of the material, carrying with it biocides (which are to some extent water soluble) and other hydrophilic compounds from the bulk to the surface, resulting in the leaching of these compounds from the material into the surrounding environment. This observation appears to be supported by numerous studies explaining the leaching of biocides when the building materials are exposed to water [44,47,73,74]. These studies also indicate that the contact time has a significant impact on the leaching intensity. Over a long period of contact, the present concentration of biocides (SVOCs) in materials is depleted. This is due to the fact that the volatile components (VOCs/SVOCs) are continuously emitted, while the reservoir of these in the materials is limited. As a result, the concentration gradient between the surface of the material and the gas phase decreases, and consequently, the emission rates are reduced [75].

On the other hand, during the aging process (CPLAP and WLAP), the acquisition rate of aged materials increased to 6 ± 2% for AFP and 10 ± 4% for AP. This increase can be attributed to the application of cleaning products (containing more than 30% water) or to water, which facilitates the solubilization of biocides incorporated into the material matrix, thus promoting their leaching. In addition, the relatively high temperature (T = 38 °C) generated by the lamps promotes the diffusion-driven emission (evaporative transport) of these active substances, especially during the first three weeks of exposure, to become stable thereafter at very low emission rates (e.g., TMetdediol = 2 ± 0.2 µg m⁻² h⁻¹). These results were also confirmed by Wolkoff's studies [76,77]. Moreover, biocide emission from the material to the surrounding environment becomes more important when the wet/dry cycle is introduced, especially when the material remains wet during the entire leaching period [48]. The latter can explain the obtained lower emission rate from the aged or incubated aged materials (e.g., TMetdediol = 2 ± 0.2 µg m⁻² h⁻¹) compared to the incubated native material (e.g., TMetdediol = 10 ± 2 µg m⁻² h⁻¹).

These results show that aging and incubation have a significant effect on the emission of biocides from the antifungal paint, which raises the following questions: Are biocides responsible for the mortality of spores initially inoculated on native samples? Will they have the same efficiency against fungal growth after the material is subjected to aging and incubation processes?

### 3.4. Assessment of the Effectiveness of Biocides in Decorative Materials

A nutrient solution (NS) was added to the native or WLAP samples to estimate the fungicidal effect of biocides present in the decorative materials. The addition of this solution was intended to promote the transfer of biocides present in the applied paints to this solution. Moreover, in the case of absence of any antifungal substances (PEC alone, for example), it will provide all the necessary nutritive and energy elements to ensure the inoculated spores' growth.

The quantitative evaluation (Figure 9) showed that the concentration of inoculated spores was (2 ± 3) × 10² CFU cm⁻². This concentration increased to (8 ± 2) × 10⁵ CFU cm⁻² for the NS alone and to (2 ± 1) × 10⁶ CFU cm⁻² for the native PEC. However, no sign of fungal growth was detected on the native AFP (with or without NS). This reveals that the biocides present in the AFP have been diffused into the NS and possess an antifungal effect, preventing mold growth on the NS. The lack of fungal growth on the WLAP AFP shows that the paint does not contain enough bioavailable elements to support fungal
growth; however, once the NS was added, the concentration was similar to that of the initially inoculated spores ((2 ± 2) × 10² CFU cm⁻²) due to the inactivation of the biocide action. These results are coherent with those presented in the previous section, where the emission rate of biocides from the aged AFP was less than that from the native AFP due to the depletion of biocides from the material. Therefore, the aged material does not afford the optimal protection of that provided by the material in its native state.

<figure><img src="image_13.png" /><figcaption>**Figure 9.** Representation of fungal growth (CFU cm⁻²) on the nutritive solution (NS), polyester cellulose (PEC) alone, and antifungal paint (AFP) in its native (native AFP) or water and light aged (W LAP) state with or without the addition of the NS. The y axis is scaled to Log10. Error bars represent standard errors of 3 measurements.</figcaption></figure>

For normal acrylic paint, the results are the same as those obtained previously (Figure 6). Normal AP promotes fungal growth in both native ((5 ± 5) × 10⁵ CFU cm⁻²) and aged ((2 ± 0.7) × 10⁷ CFU cm⁻²) states, despite the presence of biocides (Figure 10). That is, the biocides used in this paint are intended to preserve the paint and not to protect it against fungal growth [78,79]. Furthermore, the addition of NS on the native or aged material allows an increase in the fungal concentration (from (5 ± 5) × 10⁵ to (7 ± 4) × 10⁷ CFU cm⁻² for the native AP and from (2 ± 0.7) × 10⁷ to (9 ± 2) × 10⁷ CFU cm⁻² for the WLAP-AP); this is due to the addition of nutrients that further promote the fungal growth.

Vacher et al. performed, in a second part of their study, an experiment almost similar to the one realized in this study by adding a complete medium to estimate the fungicidal effect of the substrate. They reported that the acrylic paint combined with biocide-free plasterboard or with aluminum allows a rapid infestation after 10 days of incubation. However, when the paint was applied to the biocide-treated plasterboard, a slower mycelia growth was noted on this substrate after 21 days. On the other hand, glycerol paint allows a rapid fungal infestation regardless of the nature of the substrate (with or without fungicidal substance) [14].

These results show that the used biocides in the AFP provide a slower biodegradability of the substrate and a significantly longer resistance compared to other untreated substrates.

The accelerated aging process implemented in this study combines several physico-chemical parameters over a period of one month to replicate the material's "life" under realistic conditions. It uses a visible light spectrum (400 to 650 nm) to stimulate sunlight through windows. It also incorporates the application of a cleaning product or water to mimic daily cleaning habits in environments characterized by high temperatures or humidity, such as tropical regions or bathrooms. The aim of this protocol is to assess the durability of the antifungal treatment and its long-term efficacy under difficult conditions.
<figure><img src="image_14.png" /><figcaption>**Figure 10.** Representation of fungal growth (CFU cm⁻²) on the nutritive solution (NS), polyester cellulose (PEC) alone, and acrylic paint (AP) in its native (native AP) or water and light aged (W LAP-AP) state with or without the addition of NS. The y axis is scaled to Log10. Error bars represent standard errors of 3 measurements.</figcaption></figure>

The combined exposure to light, high temperatures, and water can have a synergistic effect on material degradation. UV light degrades hydrophobic compounds and photoactive additives and triggers photodegradation reactions at the ester group of the polymer matrix [80–82]. These reactions make the paint more porous and more likely to absorb water. Simultaneously, high temperatures accelerate polyacrylic degradation and promote the evaporation of volatile components, including solvents and biocides [77,83,84]. These changes alter the paint’s surface chemistry and reduce its water resistance. Additionally, repeated exposure to water, particularly during a drying and wetting cycle, can lead to solubilization and loss of organic pigments, surfactants, and other water-soluble compounds [36]. This results in the loss of molecular weight and color lightening or further physical and chemical degradation by promoting moisture retention in the paint structure [36]. Following wipe-cleaning with water, the water penetrates the film, and a phase separation mechanism occurs, causing surfactants and any other water-soluble compounds to migrate to the film surface [85]. This migration is influenced by a number of factors, including the porosity of the material and the external environmental conditions (temperature, pH, and relative humidity) [36,86]. Once deposited on the surface, surfactants can either be degraded by light exposure or removed by aqueous cleaning agents and wiping. These cleaning processes contribute to crack formation, increased surface rigidity, and pore proliferation on the film [87]. The ionic strength and pH of cleaning solvents also play a role in paint film aging [37]. In particular, solvents with a pH greater than eight or less than or equal to five favor solvent-induced swelling, which further affects the paint’s structural integrity [36].

These aging conditions not only damage the paint but also complicate interactions between molds and biocides. The depletion of biocides during aging and cleaning reduces the material's resistance to microbial growth. In addition, prolonged exposure could lead to the development of other microbial species, as successive contaminations enable microorganisms to exploit degraded substrates and microbial by-products (e.g., organic compounds or dead cells) to support their growth [18,55,88].

Thus, the process of accelerated aging highlights the interconnected nature of environmental stresses and material degradation and also underscores the significant challenges involved in predicting long-term material performance and antifungal efficacy under diverse and dynamic conditions.
**4. Conclusions**

This study evaluated the sensitivity of two commercial acrylic paints, normal acrylic paint (AP) and antifungal acrylic paint (AFP), to fungal growth, as well as the effects of accelerated aging on their antifungal performance. The investigation was carried out in four key stages.

**Stage 1: Paint characterization**

These analyses revealed that both acrylic paints contained sufficient proportions of the essential elements required for optimal mold growth, notably carbon (>2%), phosphorus (>0.1%), and calcium (>0.005%). However, some elements, such as magnesium in AFP, were detected at very low concentrations.

**Stage 2: Biodegradability of two acrylic paints under different aging conditions**

* Antifungal acrylic paint, in its native or aged state, protects the polyester cellulose wall covering against fungal growth, thanks to its biocide content. In contrast, normal acrylic paint, which contains biocides mainly to preserve it in a liquid state, promotes fungal growth.

* The aging process with a cleaning agent offers additional protection of the material against fungal growth due to its antifungal ingredients. On the other hand, the aging process with water leads to the deterioration of the material and favors a higher fungal growth compared to the native material.

**Stage 3: Biocide depletion during aging**

Antifungal acrylic paints showed significant biocide depletion under accelerated aging conditions involving dry/wet cycles at high temperatures (38 ± 6 °C) and moderate relative humidity (25 ± 17%). Incubation at high humidity (95 ± 5%) further accelerated biocide loss, reducing the paints' ability to resist fungal growth over time.

**Stage 4: Assessment of the effectiveness of biocides**

This stage investigated the main cause of mold mortality in the antifungal acrylic paint. To this end, a nutrient solution was applied to provide additional nutrients for fungal growth and to facilitate the diffusion of biocides from the materials. The results demonstrated that biocides in the antifungal acrylic paint diffused into the nutrient solution during incubation, effectively inhibiting fungal growth. In contrast, normal acrylic paint in all tested conditions (native or aged, with or without nutrient solution) supported fungal proliferation, indicating that acrylic resin, despite its complex chemical structure, exhibits biodegradability.

This study reveals a complex relationship between material composition, environmental exposure, and microbial resistance, providing critical insight into the durability and biodegradability of these coatings. Furthermore, it highlights the importance of optimizing material composition and strictly controlling environmental parameters such as temperature, humidity, and light exposure, which are key factors in aging, fungal germination, and biocide depletion, with a view to preserving the functional properties of wall coatings and mitigating the risk of biodegradation over time.

**Author Contributions:** Conceptualization, N.Z.F., N.L. and Y.A.; methodology, N.Z.F., N.L. and Y.A.; data curation, N.Z.F.; validation, N.Z.F. and Y.A.; formal analysis, N.Z.F. and T.B.; investigation, N.Z.F. and T.B.; writing—original draft preparation, N.Z.F.; writing—review and editing, T.B., N.L. and Y.A.; visualization, N.Z.F. and Y.A.; supervision, N.L. and Y.A.; project administration, N.L. and Y.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by French Environment and Energy Management Agency as a part of the Treat Aging project, grant number 1962C0012 (2019), and financed by Pays de la Loire region, grant number 49185 (2019).

**Data Availability Statement:** Data are contained within the article.
**Conflicts of Interest:** The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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