Thin-layer drying by coating of a viscous product on a hot metallic surface is studied from the point of view of heat and mass transfer. An experimental device has been built up in order both to provide and to estimate the heat flux density at the interface between the hot plate and the drying sample. Results are presented for alumina sludge drying. The determination of the interfacial heat flux is obtained from temperature measurements in the metallic plate and the solution of an inverse conduction problem. An analytical direct model is made using the quadrupole formalism and the system transfer function is calculated. The inverse problem is solved using Beck's sequential function specification method. Intrinsic drying kinetics are obtained by an energy balance.