This paper focuses on the use of modified nano-clay particles as a controlled release system for biocides from building materials. Different (model) biocides were incorporated in a biocide/nano-clay composite and subsequently the release of the biocides was monitored under different environmental conditions. In addition, the biocide/clay material was formulated into a model finishing material (gypsum) to evaluate the antifungal activity. Intercalation of biocides in modified nano-clays was found to significantly prolong the release of the biocide and prevent premature leaching of the biocide from the building material. Release rate of the biocide could be tuned by selection of the type of modification used for the nano-clay platelets. Even after prolonged leaching up to 45 days in artificial rain tests, gypsum samples containing biocide/clay composites did not show any fungal growth, whereas gypsum samples containing pure biocide had lost their antifungal activity after exposure to artificial rain for 7 days or more, demonstrating the potential of this technology for practical applications. The presented approach is very versatile, and may be used for a large variety of biocides and is envisioned to be applicable to different construction and finishing materials, including waterborne paints. To optimize the performance in a specific application area, the leaching or release process of the nano-clays should be known in the different application materials, and consequently requires alternative testing methods, e.g. methods which characterize the fungal growth as a function of release in more detail. Although correlation with practice requires further investigation, the presented method gives a good first indication for prolonged protection of building materials.