The Drying Behaviour of Building Materials Treated with Anti-graffiti

Anti-graffiti coatings are often used to protect facades against unwanted graffiti. Despite the fact that anti-graffiti are widely used, their effect on the drying behaviour of the materials is not well known. Recommendations on their application as well as product documentation generally only considers their water vapour permeability without taking into account that the drying behaviour of a material is largely governed by liquid water transport. The paper reports the findings of a research on six types of anti-graffiti coatings (permanent and sacrificial, water repellent and not) applied to two substrate materials (fired-clay brick and calcium silicate brick). The effect of the anti-graffiti coatings on the drying behaviour of these materials is evaluated by means of drying tests performed at different RH. The drying behaviour of the same material impregnated with different types of water repellent products is given for comparison. The obtained results are analyzed as a function of product composition and the properties of the substrate materials, such as porosity and pore size distribution. The possible consequences of the application of the tested anti-graffiti coatings on common damage processes, such as frost and salt crystallization, are discussed.