This study presents the results of sorption measurements and analyzes their applicability in the determination of the moisture diffusion coefficient in the porous media in which these processes occur. The test involved three classes of autoclaved aerated concrete density: 500, 600 and 700. The sorption processes under examination covered practically the whole range of hygroscopic humidity from RH = 0% up to RH = 98%. The idea of the experiment was to place dry samples of the tested concretes to

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... 98% relative humidity stimulated by the saturated water solution of K 2 SO 4 . The tests were performed until weight stabilization of all samples, which took about 10 months. On the basis of the results obtained, individual diffusion coefficients were determined using two different calculation procedures: the square root of time method and the logarithmic method. The first method applies to the initial stage of the process, while the other is used at its advanced stage. Both measurement methods were assessed in terms of their applicability and compatibility.