Several properties of ceramic materials such as mechanical strength, acoustical characteristics, etc. are related to their degree of porosity. Traditional methods to estimate the porosity of materials used in construction are two slow and tedious to perform, rising the need of searching new techniques to get the degree of porosity in a fast and robust way. In this paper, a system to estimate indirectly the degree of porosity by classifying ceramic samples according the changes produced in the radio frequency response is presented. The proposal uses a patch antenna to extract relevant features that help to estimate the class of a given ceramic sample. Results show that it is possible to classify samples based on the changes of the spectral response that varies according their level of porosity since they affect the propagated waves around the antenna when they are located on the surface of the patch, and so impinges upon directly on resonance frequency and bandwidth of the antenna.