DRAFT 12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012 1 A CRITICAL POINT OF VIEW AND RECENT STUDY WITH INNOVATIVE TOOL TO EVALUATE THE PENETRATION DEPTH OF A WATER REPELLENT TREATMENT ON POROUS INORGANIC MATERIALS Valeria Di Tullio 1 , Vasco Fassina 2 , Anna Maria Mecchi 3 , Ilaria Nicolini 3 1 Institute of Chemical Methodologies-CNR, Via Salaria km 29.300 – 00015 Monterotondo Stazione (Roma), Italy 2 Superintendence of Cultural Heritage of Veneto – Santa Croce 770 , Venezia, Italy 3 Institute for the Conservation and the Valorization of Cultural Heritage – CNR, Via Salaria km 29.300 – 00015 Monterotondo Stazione (Roma), Italy Abstract Water repellent treatment is one of the most important interventions usually carried out in the conservation of stone materials. It is essential to choose a suitable product and then to ascertain its effect on a medium and long term basis. Obviously only after experimentation, first in laboratory and after in situ, the behavior of the treatment can be determined. Recently the CEN TC 346 has been trying to establish a common methodology to test in laboratory water repellent products applied to porous inorganic materials. The methodology and time of application can strongly influence the depth of penetration of a treatment into a porous structure. In this paper, a preliminary review by analyzing and highlighting some crucial elements in the study of water repellent treatment in stone specimens has been carried out.. Besides, a comparison has been made between the results of our recent studies of water repellent treatment on a sandstone and a biocalcarenite with the aim of showing the close correlation between the time of application of the product and its penetration depth on stone evaluated by Unilateral NMR depth profile and capillarity absorption . Keywords: stone treatments, water repellent, penetration depth 1. Introduction Water repellents are used to prevent or to reduce water penetration into stone and thereby reducing the decay of the materials. As a consequence it is essential to choose a high quality water repellent product and then to ascertain its effect on a medium and long term basis. Obviously only after experimentation the behavior of the treatment can be determined. As it is well known, it is very difficult to carry out the experimentation in situ because numerous variables must be taken into consideration. For instance, stone properties can vary widely for the same type of stone depending from which part of the quarry the block of stone was taken. For in situ experiments stone properties depend both on the condition of the stone surface and the atmospheric environment. For this reason, it is easier to perform experimentation in laboratory where the experimental conditions can be better controlled. Obviously, to obtain a direct comparison of the results from several studies, it is necessary to have a protocol regarding the most important parameters of evaluation and the methods of application of the water repellent treatment. Besides, there are other factors that are difficult to