Résumé Nous avons procédé à un examen des principaux produits de traitement de la pierra, car leur application est toujours plus répandue dans le domaine de la conservation et de la restauration des monuments historiques. On constate que la plupart des essais effectués pour obtenir une consolidation en profondeur de la pierre s'est soldée par des échecs, souvent attribués à la trop faible profondeur atteinte par le produit de consolidation. On peut se demander si un traitement superficiel bien étudié et réalisé en tant que tel n'aurait pas plus de chances de réussite.

Summary Stone preservation must be approached as a real problem of applied physical chemistry where the knowledge of the technological and scientific properties of chemicals used for such treatment is of primary importance. This is why we have decided to examine the main products for treating stone and to refer to examples of laboratory tests and also practical applications on historic and artistic monuments. Such an investigation raised numerous questions, since the problem of stone preservation has not been solved and there is no valid philosophy fundamental to the preservation of monuments. Significant progress achieved in recent years in the field of synthetic resins has attracted the attention of specialists undertaking restoration and research laboratories. The rather approximate results obtained after tests with monomers and polymers first brought about a wave of enthusiasm, quickly followed however by reactions for too pessimistic. The properties and results required of chemical must be rational and realistic, based on scientific knowledge, not chimerical and contradictory. A monument must be left with its “original appearance” as long as possible, that is to say, everything must be done to preserve its shape, location and building materials directly chosen by the artist. Replacing old stone by new often causes damage comparable to transforming an architectural motif. Once the imperative need for preservation of a stone construction has become obvious, the remedy proposed was consolidation as deep as possible. In spite of endeavour and experience in this field dating back150 years, this method is still costly and almost impossible to carry out successfully because of the technical difficulties involved. Most tests undertaken to obtain deep consolidation were finally failures, often put down to the fact that the chemical failed to penetrate to the required depth. This seems to point to the theory that properly prepared surface treatment, carefully applied and specifically designed for the purpose, might be more successful.