The different effect of two paint systems on moisture buffer capacity of traditional and modern plasters

Abstract

Plasters can be finished with paint systems that can affect their moisture storage and transport properties. To confirm that, eight traditional and modern plastering mortars and pastes – based on cement, natural hydraulic lime, air lime, earth and gypsum - were coated with a vinyl paint (A) and an acrylic paint (B) and underwent the same hygroscopic characterization of the bare mortar samples. The effect of paint system A on water vapor adsorption and moisture buffering was small, in some cases positive. However, all the plasters painted with system A showed lower water vapor permeability than the bare plasters. The variation in the thickness of equivalent air layer was not the same for all the plastering mortars and pastes, suggesting that the different plastering substrates were still involved in the hygroscopic mechanism. The application of paint system B, instead, significantly reduced the hygroscopic behavior of the plasters, leveling their responses. The two paints, produced for different scopes and so with different kind and contents of constituents, have a diverse effect on those properties. Therefore, to optimize the passive contribution that plasters may have to indoor comfort, it is important to make a conscious choice when choosing paint finishing systems.