A method for detecting at least one roughness in a face of an abradable layer in a fan casing is provided. The method includes a step of depositing on the abradable layer a first coating and a second coating covering the first coating. The first and second coatings have respective thicknesses (N1, N2) and a physical appearance that differ from one another. Local appearance of the first coating is indicative of a need for a localized touch-up, and local disappearance of the first coating and the second coating is indicative of a need for a localized replacement of the abradable layer.