An ash deposit growing model based on surface growing theory is developed in order to represent the coal fired ash deposits. The predicted characteristics are compared to physical and chemical measurements of a typical ash deposit collected from an existing coal fired power plant located in the south of Brazil. Several structures were generated and compared to scanning electron images of ash deposits collected from the steam superheater section. The physical and chemical characteristics of the ash deposits, such as porosity, pore size distribution and fractal dimension of a typical ash deposit were measured using SEM image. All the images were analyzed using Imago software. Also, the existing ceramic phases were quantified using EDX detection and X-ray diffraction. The proposed random trajectory particle deposition model led to good agreement when compared to the macro quantities such as porosity and fractal dimension. It is expected that the modeled porous structure can be used for further heat transfer analysis and evaluation of coal-fired steam boiler designs. (C) 2011 Elsevier B.V. All rights reserved.