Salts causes surface damages and efflorescence for masonry walls. This has increased the interest to understand the salt transfer phenomena taking place in porous matrix. There is still however a lack of published transport data in the literature. Especially the diffusion coefficients of salts in different brick structures are lacking. In this work a method for measuring the rate of diffusion of salt in ceramic material is presented and applied to the measurement of diffusivity of NaCl in three different brick materials. Fick's first law of diffusion was applied to calculate the diffusion coefficients in a pseudo stationary state by means of linear regression analysis. The result for the diffusivity of 0.05 molar NaCl in water in new Finnish red brick was (0.499 +/- 0.004) (*) 10(-5) cm(2)/s in the temperature of 25 +/- 0.05degreesC. The corresponding values for the old light brick and old dark brick was (0.453 +/- 0.008) (*) 10(-5) cm(2)/s and (0.337 +/- 0.009) (*) 10(-5) cm(2)/s respectively. The diffusion coefficients are given as an effective diffusion coefficients calculated with the porosity value measured to each of the specimen. The concept of salt diffusion and diffusion mechanism inside the porous matrix are also discussed. (C) 2003 Kluwer Academic Publishers.