Especially in humid or wet environments, such as bathrooms and kitchens, silicone sealants must be protected by the use of biocides from the growth of microbiological agents, i.e. fungi (mould or yeast), bacteria, or algae, to ensure longevity of the aesthetic aspect of sealing joints. Environmental aspects of using biocides, efficacy of active ingredients, and appropriate test methods to be used in order to assess ultimate performance and predict service-life durability under various weathering conditions (underwater leaching, UV exposure, outdoor) are all important aspects that require careful consideration.
Based on the experiences acquired in Rohm and Haas and Dow Corning laboratories, respectively, we have shown the importance of pre-conditioning the specimens, and selecting the appropriate test method to assess the anti-fungal protection of sealants. Among the various methods developed for that purpose, i.e., CAN2-19.0-M77, Wallhauser test method, NFX 41-514, ISO 846 and ASTM G21-96, we have shown that ISO846, method B, is the most appropriate for assessing the efficacy of biocides in protecting sealants against fungus growth in sanitary environments. We also discuss the choice of the appropriate inoculums and challenge testing conditions, as well as the key aspects that are important for proper interpretation of the ratings resulting from the challenge tests.
Comparative testing carried out with various silicone sealant systems enabled the identification of active ingredients adequate to provide durable protection of a cured silicone sealant, in particular after underwater leach-out conditioning, which for weatherproof sealing in residential glazing and sanitary applications is an important requirement. Comparison of the ratings obtained before and after underwater leaching provides therefore insights that allow estimation of the decrease of anti-fungal efficacy over time during service-life. Key selection criteria that an effective biocide needs to fulfill are also suggested.