Historical Constructions, P.B. Lourenço, P. Roca (Eds.), Guimarães, 2001 353 ABSTRACT: There is a clear need to develop and systematise a methodology to approach interventions on ancient renders. In fact inadequate interventions, with systematic resource to modern solutions, originated in Portugal a situation characterised by the disappearing of original lime renderings and finishings and caused several anomalies due to functional incompatibility between pre-existing elements and new materials. The research project Oldrenders, accomplished by researchers from LNEC in collaboration with the construction enterprise STAP - Reparação, Consolidação e Modificação de Estruturas, SA., and partially financed by Agência de Inovação, has as main objectives the definition of such a methodology and the preparation of criteria to support the selection of substitutive compatible mortars. This paper synthesises the aims and conclusions of the Project. 1. OBJECTIVES OF THE RESEARCH Interventions on ancient buildings included for too long the systematic remotion of the original renders, plasters and finishings and its substitution by renders and plasters based on Portland cement, painted with products based, first in oil paints and then in acrylic and vinylic resins. In the meantime, the theory of conservation has more and more pointed out the historic and aesthetic importance of preservation of material evidences and their fundamental part in the definition of formal and material authenticity of historic artifacts. Several studies recently developed at LNEC, or with LNEC’s direct support (Aguiar, J., 1999, Margalha, G., 1997, Tavares, M., 1998), contributed to modify the Portuguese idea about the architectural value and meaning of renders and finishings in the nation’s historic heritage. From a restrictive perspective - today considered as false and related to fascist paradigms – affirming the primacy of the simplicity of white lime on South of the country and of the solid expression of faced stone masonry, on the North, there was a quick evolution to the re-discover of an enormous richness of chromatic, textural and decorative expression. Indeed, external solutions completely unknown by architectural and urbanistic history till recently, were finally rediscovered, such as paintings, grafitti and sgrafitti, trompe-l’oeil, scagliole, intonachini, etc. This long oblivion originated a dramatic incapacity of “seeing” this kind of techniques, with hard consequences in the quality of our urban rehabilitation interventions. The enormous quantity of inadequate interventions in historic buildings, with systematic resource to modern solutions, created a situation characterised by the disappearing of original lime renderings and finishings. As a consequence, the surviving original decorations acquired a new patrimonial value, which obliges new intervention attitudes. Actually, substitutive practices, which are still the great majority in Portuguese building restoration and urban rehabilitation, originated several anomalies due to functional incompatibility between new renders and ancient masonry, besides affecting the patrimonial and Methodologies for characterisation and repair of mortars of ancient buildings M. Rosário Veiga, José Aguiar, António Santos Silva and Fernanda Carvalho Laboratório Nacional de Engenharia Civil (LNEC), Lisbon, Portugal