Conditions Influencing Mould Growth for Effective Prevention of Wood Deterioration Indoors (original) (raw)
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The Role of Transient Wetting on Mould Growth on Wooden Claddings
Energy Procedia, 2015
Mold growth on the surface of wooden façades is usually dealt with by using surface treatment such as paint with fungicides. However, new developments in architecture are moving towards less use of coating, and more use of untreated wooden claddings. Mould growth is well understood and described, and several models for predicting mould growth on building materials exist. It is commonly known that mould growth is directly controlled by the climate which the wood is exposed to. Several authors identify humidity, temperature and time as the main drivers of mould growth. However, most of the current growth models developed are based on laboratory measurements at stable climatic conditions. Consequently, these models are less suitable for prediction of mould growth on exterior surfaces exposed to rapidly changing weather conditions. This paper analyses the effect of variations of meteorological data on the mould growth on wooden claddings. An experimental setup of wood samples was exposed to outdoor conditions and hourly weather conditions as well as the mould growth at different intervals were measured. The measurements were supplied with 1-D Heat And Moisture (HAM) simulations to provide a more accurate estimate of the conditions on the surface of the samples. The purpose of the analysis was to evaluate if an existing mould growth model might be applicable also for predicting outdoor mould growth. Several profiles of temperature and moisture were continuously monitored on different locations of an eight-story building made from Cross Laminated Timber (CLT). The results from the analysis of the samples of wood cladding were used to model the mould growth on different locations of the building. Also the drying effect of wind around the building was studied. The study shows that there is large variation of potential mould growth on the façade of the building.
Laboratory study to determine the critical moisture level for mould growth on building materials
International Biodeterioration & Biodegradation, 2012
The susceptibility of building materials to mould growth varies. Some are tolerant to high relative humidity in the ambient air without mould growth occurring, while others are less tolerant, and mould can grow in relative humidity as low as 75%. Within a building, constructions are exposed to different temperatures and relative humidities. To minimise the risk of microbial growth, building materials should be chosen that are tolerant to the expected conditions. In this study, the critical moisture levels for ten building materials with a range of expected critical moisture levels (wood-based materials, gypsum boards and inorganic boards) were evaluated. Samples of the building materials were inoculated with spores from six species of mould fungi (Eurotium herbariorum, Aspergillus versicolor, Penicillium chrysogenum, Aureobasidium pullulans, Cladosporium sphaerospermum, Stachybotrys chartarum) and incubated in test cabinets at specified temperature (10 C and 22 C) and relative humidity conditions (75e95%); growth of mould was analysed weekly for at least 12 weeks. One of the conclusions is that two similar building materials or products may have considerably different resistance to mould growth, and so the results from one type of building material cannot be applied to the other. Also, in order to compare results from different tests, it is important to use the same test method. It is also important to state the temperature at which the critical moisture level applies and how long the material is exposed to the temperature and relative humidity conditions during the test.
Development of a new rapid method for mould testing in a climate chamber: preliminary tests
European Journal of Wood and Wood Products, 2013
The purpose of this study was to develop fast, simple and robust solid wood mould testing methods for the use in small-scale laboratory tests. The objective was to investigate mould susceptibility of different wood materials within the batches. The proposed method is based on natural contamination of non-sterile surfaces in climates conducive to mould growth. For this purpose, a climate chamber with regulated temperature and relative humidity was used. The conditioning chamber was divided into upper and lower chamber by a thin layer of stainless steel placed horizontally above the fan to minimise air circulation to the sample in the upper compartment. Mouldinfected samples from outdoor tests were used as a source of mould inocula, and test trials were conducted on Scots pine (Pinus sylvestris L.) sapwood. Samples were suspended from the top of the upper chamber, and the chamber was exposed to different temperature and humidity levels. Severe mould infestation was observed after 12-14 days of incubation. Visual mould rating was then performed. Regardless of some constraints, this test method was very simple, fast, and effective. More importantly, unlike other test methods, it closely models mould infestation as it would occur under natural condition. Entwicklung eines neuen Schnellverfahrens zur Prü fung von Schimmelbefall in einer Klimakammer-Vorversuche Zusammenfassung Zweck dieser Studie war die Entwicklung eines schnellen, einfachen und robusten Verfahrens zur Prüfung von Schimmelbefall auf Massivholz im Labor. Ziel war es, die Anfälligkeit von in der Prüfkammer unterschiedlich angeordneten Prüfkörpern für Schimmelbefall zu untersuchen. Die vorgeschlagene Methode basiert auf natürlicher Kontamination nicht steriler Oberflächen in Klimata, die Schimmelwachstum fördern. Hierfür wurde eine Klimakammer mit regulierbarer Temperatur und relativer Luftfeuchte verwendet. Die Klimakammer wurde mittels einer horizontal über dem Ventilator angebrachten dünnen Edelstahlplatte in einen oberen und einen unteren Teil abgeteilt, um die Luftzirkulation im Bereich der Prüfkörper in der oberen Kammer zu minimieren. Von Schimmel befallene Prüfkörper aus Freilandversuchen dienten als Infektionsquelle. An Kiefernsplintholz (Pinus sylvestris L.) wurden Testversuche durchgeführt. Die Prüfkörper wurden an der Decke der oberen Kammer aufgehängt und in der Kammer wurden verschiedene Temperatur-und Feuchteniveaus eingestellt. Nach 12-14 Tagen wurde starker Schimmelbefall festgestellt. Anschließend wurde der Befall visuell bewertet. Abgesehen von einigen Einschränkungen erwies sich diese Methode als sehr einfach, schnell und effektiv. Noch wichtiger war jedoch, dass dieses Verfahren, im Vergleich zu anderen Prüfverfahren, Schimmelbefall am realistischsten modelliert.
Building and Environment, 2009
We report the results of a study to evaluate the growth rate of three species of mould on plasters, finishes and paints typically used in structures with heavy weight building envelopes. The aim was to determine the influence of the chemical composition (in terms of organic fraction of the materials) on the growth rate of moulds. The study was carried out in the following steps: -characterization of materials;inoculation of mould spores (3 species) on 7 types of material (2 plasters, 3 finishes, 2 paints); -growth in a climatic chamber (23 C and 90% RH); -analysis of the mould growth rate using various experimental techniques (fluorescence microscopy analysis, thermogravimetric analysis, etc.). Results show a clear correlation between the organic substances contained in paints, plasters and finishes and the growth rate of the mould. This study is part of a more general research program which addresses the effects on indoor environment air quality based on the European directive 2002/91/EC. This directive specifically indicates that energy consumption in buildings should be limited and sets threshold values for the thermal resistance of the building walls and windows. As a consequence window manufacturers are improving the thermal property of windows by reducing the air permeability, which may increase the indoor and surface relative humidity percentage (RH%) and lead to the development of mould in the indoor environments.
HAM and mould growth analysis of a wooden wall
International Journal of Sustainable Built Environment, 2013
The aim of engineers is to design structures, while minimising their energy dependence and create a suitable environment for living. Some of the most important factors for maintaining the indoor environment are temperature and humidity. Unsuitable combinations of heat and moisture (HAM) could indicate a danger of mould growing. The mould's existence influences the reliability and lifespan of a structure. Some materials, for example wood, are very sensitive to mould growth. To analyse a structure for mould growth risk it is necessary to know the values of temperature and relative humidity on the surfaces and inside of structures. There are two possibilities to acquire these quantities; taking measurements at a construction site or in a laboratory, or applying numerical solutions using an accessible programme. One such programme is Wufi, which has been developed especially for HAM analysis. An advantage of measuring at the construction site is the reality, which is not affected by numerical errors. On the other hand, numerical analysis usually needs lower costs and does not demand so much time to simulate long term periods. From the point of view of accuracy, it is suitable to verify the numerical solution with measurements. The aim of this paper is threefold. First, to analyse the risk of mould growth. Second, it presents a verification of numerically calculated data using Wufi 2D against actual measurement data acquired from a real structure, which is presented by a low-energy house located in Oulu/Finland. Third, to prove that the form of low-energy building structures do not increase mould growth risk. After carrying out the verification, the received outcomes are utilised for mould growth analysis. For an expression of reality in the numerical solution, a transient simulation was needed. The received outcomes were then used for mould growth analyses. There is a possibility to predict real mould growth risk inside the structure and on its surfaces, corresponding to the critical relation between temperature and relative humidity, which separates favourable and unfavourable areas for mould growth.
Validation of critical moisture conditions for mould growth on building materials
Building and Environment, 2013
Materials that are stored or used in damp conditions may be subject to mould growth. However, all materials are not equally susceptible; for each specific material, there is a critical moisture level for mould growth. If this is exceeded, there is a risk that mould fungi will develop on the material. This level can be determined in accelerated laboratory tests, at constant temperatures and relative humidity (RH) favourable to mould growth. Within a building however, these parameters are expected to vary from one part of the construction to another, and are seldom constant; there is fluctuation in temperature and RH due to seasonal or shorter-term variations. In this study, test pieces of the same materials tested in a laboratory environment were placed in three outdoor ventilated crawl spaces and three outdoor ventilated attics, where the temperature and RH varied, and mould growth on the test pieces was studied over 2.5 years. Material-specific mould growth curves were produced based on critical moisture levels, as determined in laboratory experiments under constant temperature and RH. When the actual conditions of RH and temperature exceeded these curves, there was mould growth on the test pieces if the time was sufficiently long. The conclusion from the study is that although conditions in laboratory studies are simplified and accelerated, the results serve well to indicate mould growth within a building construction.
Resistance of different wood-based materials against mould fungi: a comparison of methods
European Journal of Wood and Wood Products, 2020
Wood-based materials are generally prone to colonization by mould fungi and other discoloring microorganisms, but their resistance to fungal discoloration varies. Different standardized test methods for determining the susceptibility to mould fungi have been used to evaluate various wood-based materials, but the obtained results suggest that mould resistance depends on the method applied. Therefore, this study aimed at a comparative evaluation of two commonly used methods for determining the mould resistance of wood-based materials, i.e. the chamber method according to BS 3900—Part G6 and the malt agar plate method according to ISO 16869. Solid wood, wood fiber insulation boards and wood polymer composites were inoculated, incubated for different time intervals, and assessed with regard to superficial mould growth. Mould growth ratings obtained with the two methods did not correlate well, neither within one type of material nor across different materials, which can be attributed to ...
Mould Growth Experiments of Full Scale Wood Frame Wall Assemblies
This paper reports on a full-scale experimental investigation of the mould growth on different types of wood products used for sheathing and framing wall assemblies. Objectives included examination of the difference in mould growth in full-scale wall systems under different temperature and humidity conditions for treated and untreated wood products. Importantly this study used full scale wall assemblies; to date mould growth studies have only been performed within a laboratory on small samples of materials. Moreover, this study recreates the conditions which evidently cause mould growth on full scale wall assemblies. Tests were performed within a climate chamber on three wall assemblies. The scope of the study includes both the sheathing and framing components, but this paper focuses mainly on the sheathing. Results indicate that the relative humidity conditions needed for mould growth to occur on wood in a reasonable time (less than several months) are higher than a surface relativ...
Laboratory Investigations of Mold Growth on Transverse and Longitudinal Wood Surfaces
Applied Sciences
The possible influence of anatomical sections of wood on mold growth was investigated by means of a laboratory experiment. The selected fungi, Aspergillus sp., Penicillium sp., and Alternaria sp. were inoculated by spraying on the surface of wood specimens prepared from pine (Pinus sylvestris) and spruce (Picea abies). The incubation was carried out under stable environmental conditions (temperature of 22 °C, relative humidity of 75, 87, and 95%) over three months. Mold growth was evaluated based on regular microscopic and macroscopic observations. The recorded mold coverage fractions and the qualitative indicators of mold development were later expressed by a dimensionless mold index. The differences in mold growth in the anatomical sections of wood were found to be relatively insignificant. In contrast, comparison of measured data with other experimental studies showed large differences, especially in the initial growth phase. The discrepancy is probably related to differences amo...