A versatile and modular nuclear magnetic resonance (NMR) instrument is described that is particularly suited for the study of moisture transport in porous media such as various building materials in which moisture can give rise to several kinds of damages. Quantitative measurements of one‐dimensional moisture profiles and their time evolution can be performed on cylindrical samples having a diameter up to 20 mm with a spatial resolution better than 1 mm. Water absorption and drying experiments on various building materials demonstrate that the instrument can also be used for materials containing relatively large amounts of magnetic impurities, which until now were hardly accessible by NMR techniques. ©1994 American Institute of Physics.