Cultural Heritage materials are often porous and in many cases present decay in several forms. Because of their historical value, they must be protected. Nowadays, this type of materials is menaced by the phenomenon of graffiti, which not only is normally aesthetically unwanted, but it also damages the historic substrates due to the penetration of paints and the methods used during the elimination process of graffiti. In order to protect these substrates against this phenomenon, anti-graffiti products can be used. These systems prevent the penetration of dyes and paints into the surface, facilitating the removal of graffiti. However, weathered porous substrates such as those commonly found in Cultural Heritage objects, present special protection requirements which are not fulfilled by the anti-graffiti currently available in the market. Considering this situation, a new anti-graffiti system with specific properties to prevent damage caused by graffiti attack in Cultural Heritage buildings has been developed within the framework of the project “Development of a new anti-graffiti system, based on traditional concepts, preventing damage of architectural heritage materials, GRAFFITAGE”, a three-year project funded by the European Commission. In this project, 10 institutions including technological centres, SMEs and public entities from 6 European countries (Spain, Germany, Poland, Belgium, Italy, Slovenia) have participated under the coordination of TECNALIA from its Construction and Territorial Development Unit. The new anti-graffiti formulation is based on a pH-sensitive silicon-based polymer charge complex and presents the following characteristics: - hydrophobicity so as to avoid or diminish problems caused by water penetration; - adequate adherence to porous surfaces; - low aesthetical variations after application so that the application of the coating is not perceived by the naked eye; - improved drying behaviour and water vapour permeability; - resistance to UV light/condensation ageing and natural weathering; - good cleaning efficiency; - its chemical composition is environmentally friendly. The formulation was tested onto 8 substrates of different porosity from 5 European countries (Spain, Germany, Italy, Belgium and Slovenia). The study of the behaviour of the coating was performed in the laboratory in a first stage and in real outdoor conditions in a second stage. Hydric and durability properties such as drying behaviour, water vapour permeability, natural weathering and UV light / condensation ageing were studied, as well as the colour and gloss variations and the water repellence. One of the most important aspects was the study of the cleaning efficiency of the coating with the aim of validating the effectiveness of the new product during the cleaning of graffiti. In order to establish the improvement with respect to existing commercial products, 4 different anti-graffiti of current use were selected and their behaviour compared with that of the new anti-graffiti formulation. The results obtained from these tests confirmed that the new product is highly adequate for the protection of Cultural Heritage porous substrates. In this sense, the anti-graffiti system developed in this EU project constitutes a promising prototype, which after further improvement with regards to its synthesis process and study of its durability properties in different environments, could be commercialized in Europe.