Water-based coatings materials, due to their desirable properties such as very good resistance to weather conditions and flexibility as well as easy application, are used for both decorative and protective purposes. The ability of the coatings to transport water can effect fungi growth, loss of adhesion, or the penetration of aggressive ions from rain into the substrate. Therefore, determining the water transport properties of water by paints is a key point in determining their protective properties.

This study investigated the effects of preparation, conditioning, and testing methodologies on the water vapour permeability properties of waterborne coatings. The study was divided into two parts. In the first part, the influence of the binder content of the paint product, the film thickness, and the presence of different substrates on the water vapour permeability values obtained was determined. In the second part, the influence of conditioning and testing methods was investigated. The conditioning method was selected based on the target use of the coating (indoor/outdoor), in accordance with the instructions in the PN-EN ISO 7783:2018-11 standard. However, due to the possibility of applying outdoor paints indoors, they were conditioned using both methods. Since the standard does not indicate how to select a test method for each group of prepared coatings, wet and dry cup methods were performed.

The results obtained show that the water vapor transmission rate decreases with increasing binder content, and the observed differences are greater for thicker coatings. The water vapor transmission through the coating on the substrate depends on the interaction between them. The coating conditioning method has the greatest influence on its ability to transport water; therefore, to determine the protective properties of the coating, it is important to choose test conditions that best represent the actual conditions in which the coating will be used.