Dampness is a common condition in old buildings and, accordingly, many paint systems specific for this type of buildings allow for application on walls with non-negligible moisture content. In spite of that, performance evaluation of these paints is normally carried out using dry substrates or even on free paint films. This paper presents a research performed on sixteen commercial paint systems: seven silicate, three silicone, three hydro-pliolite and two lime-based paint systems, as well as one common vinyl emulsion paint that served as reference. Each paint was applied and cured both on dry and damp mortar substrates. The test specimens were subjected to water vapour permeability and evaporative drying tests. The following conclusions could be drawn: (i) the way paint systems influence the drying of the substrate to which they were applied and where they cured may vary significantly depending on the moisture content of that substrate; (ii) vapour permeability, measured with specimens applied and cured on dry substrate, may be an acceptable way of predicting a paints’ influence on the drying provided that the paints are applied and cured on dry substrate or that their characteristics are not significantly affected by the moisture content of that substrate.