This European Standard specifies a method for determining the water-vapour transmission rate of coatings, coating systems and related products, intended for exterior masonry and concrete. The method is applicable to coatings and coating systems on porous substrates such as brick, concrete and renderings NOTE 1: The method is also applicable to the determination of the water-vapour transmission rate of coatings and coating systems intended for other substrates. The procedure using a porous substrate is not applicable for coatings having dry film thicknesses less than 80 µm as determined by calculation. NOTE 2: Some products, normally of low viscosity and/or very low solids content, that do not form films, or abnormally affect the porosity of porous substrates, should not be included when the water-vapour transmission rate of coating systems is determined. Their effect in practical situations should be agreed between the interested parties.