Diferencial stains on mortar-coated facades

hydrothermal simulation analysis of mechanisms and behaviors

Abstract

Differential stains, or fantômes, are characterized by the formation of visible contours on the coating, associated with moisture retention and thermophoresis, a phenomenon in which atmospheric particles preferentially deposit on cooler regions of the façade. This study analyzes how the hygrothermal performance of façades composed of ceramic blocks, mortar joints, and concrete, subjected to three finishing conditions (no paint, economic paint, and standard paint), influences the formation of these stains. The research is applied to a building exhibiting this pathology, located in Brasília, Brazil. The study evaluates the duration within the critical ranges of the isopleths for fungal development, the temperature differentials between the materials, and the occurrence of surface quasi-condensation. The results indicate that the unpainted system presents a higher risk of biological colonization due to greater moisture retention. On the other hand, the painted systems, although they reduce surface moisture, can show increased temperature differentials between the materials, which may favor the occurrence of thermophoresis when there is significant thermal contrast between the substrates.