Yes, Marfil Grey Porcelain can be used in exterior applications in very humid climates. Porcelain is a dense and non-porous material, which makes it highly resistant to moisture and humidity. Additionally, Marfil Grey Porcelain is specifically designed to be used in outdoor settings, so it can withstand the elements, including high humidity. However, it is always recommended to consult with the manufacturer or a professional to ensure that the specific product and installation method is suitable for your specific climate and conditions.