In the framework of the conservation of the Cathedral of Our Lady in Tournai (Belgium), the Royal Institute for Cultural Heritage (KIK-IRPA, Brussels) was called upon in 2012 to carry out a preliminary study of two Romanesque portals called the Mantile and Capitole portals. The aim of this study was to understand the deterioration mechanisms of the stone and to propose a conservation strategy. Both portals are constructed from the local black Tournai stone, with the exception of the 19th century restoration in Belgian bluestone. Due to the strongly deteriorated state and the large size of the portals, a detailed visual inspection survey of each stone block was necessary to obtain an overview of the actual state of conservation and to develop an adapted conservation strategy. The deterioration patterns were digitally mapped with the Metigo MAP software (fokus GmbH), using rectified photographs as a template. These mappings present a visual clarification of the location, extent and degree of the different deterioration patterns. They also enable us to evaluate and compare the deterioration patterns of both portals and can be linked to the results of the laboratory analyses.