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The main historic monuments of the Loire Valley in France are built with tuffeau. This very porous and soft siliceous limestone presents many technical and aesthetic advantages justifying its wide use. Among the most damaging degradations of tuffeau, spalling is the most destructive one. This study aimed at verifying the profiles of gypsum content observed in spalling of tuffeau at the castle of Chambord during a previous study. Here, samples from both the Castle of Chambord and from the Castle of Chaumont-sur-Loire were collected, to provide more extensive and thus representative data for monuments made out of tuffeau in the Loire Valley.For all samples, in both castles, a systematic presence of gypsum was observed in areas subjected to spalling. The gypsum content is always very low at the surface and progressively increases (always around 1%) up to the depth of the zone where the crack is present, and then decreases along depth. No other salt was detected. This study also proved that preexistent cracking is not necessary for gypsum to crystallize. All these statements are totally in accordance with the previous study, hence allowing to confirm its representativeness.

This thesis is dedicated to the establishment of a methodology to study the built cultural heritage, applied to the castle of Chambord. It consists in realizing the health record of the monument, and completing it by an experimental sequence in laboratory, in order to provide a diagnosis of the state of degradation.Historical archives about the castle were gathered and analysed to obtain mappings of dating and nature of stone. By mean of in situ observations, a mapping of degradation has been added. A synthesis of the information concerning the past and the present of the monument allowed establishing a list of the main factors associated to degradations and to a chronology of development of these degradations, so as to estimate their kinetics.Spalling, which is the most damaging and complex usual degradation, has been chosen as case of study for the diagnosis of degradation. The physic-chemical characterisations made on in situ coring lead to systematically found gypsum in spalling’s cracks. Various artificial ageing tests have been performed to enlighten the role of gypsum, its transport mode, and its origin. Atmospheric pollution including gaseous SO2 reproduces well the distribution of gypsum observed in spalling at Chambord. A global mechanism taking into account this phenomenon has been proposed to clarify the development of this degradation., Ce travail de thèse consiste en l’élaboration d’une méthodologie d’étude de monuments historiques, appliquée au château de Chambord. Il s’agit de mettre en place le carnet de santé de l’édifice, et de le compléter par une expérimentation en laboratoire, afin de réaliser un diagnostic d’altération.Les archives historiques concernant le château ont été rassemblées et analysées pour concevoir des cartographies de dates de pose et de nature des pierres. L’examen in situ des façades a ensuite conduit à réaliser des cartographies d’altération. La synthèse des informations concernant le passé et le présent du monument a permis d’établir une liste des principaux facteurs environnementaux associés aux altérations, de même que la chronologie de leur développement, pour ainsi aboutir à une première estimation des cinétiques de progression.C’est la desquamation en plaques, détérioration courante du tuffeau, à la fois la plus dommageable et la plus complexe, qui a été ciblée pour le diagnostic d’altération. Les analyses physico-chimiques réalisées sur des prélèvements in situ ont conduit à l’identification systématique du gypse dans les fissures des desquamations. Des simulations expérimentales ont été mises en place pour appréhender le rôle du gypse, son mode de transport et son origine. La pollution atmosphérique mettant en oeuvre du SO2 gazeux reproduit bien la distribution du gypse telle que mesurée dans les desquamations en plaques observées au château de Chambord. Un mécanisme incluant ce phénomène a été proposé, pour expliquer le développement de cette altération, et qui pourrait être à la base des prévisions de l’évolution des altérations, afin d’envisager le futur du monument.