Patterned Staining of Rendered Facades: Hygro-Thermal Analysis as a Means for Diagnosis

Abstract

Pathological phenomena in physical performance of buildings, such as façade staining, require accurate diagnosis and understanding of causative mechanisms in order to suggest effective remedial means. Lately, rendered façades of newly built residential buildings in Israel have developed patterned staining revealing the underlying structure. Samples from stained areas indicated selective growth of microorganisms. Typical finishes proved to support fungi growth under optimal growth conditions. However, this could not explain selective growth. Only advanced hygro-thermal analysis could explain in detail substrate-dependent surface moisture content evolutions. It showed that significantly larger moisture contents are obtained above thermally insulated parts, even in the absence of surface condensation and rain, and that decreasing the rendering's moisture diffusivity enhances these differences.