It has been clear that the water content of building structures is an important factor on carbonation of concrete by a past study using a model building at the age of 11 years’ natural exposure, not to speak of frost damage. In this paper, the water absorption experiment using specimens of ALC, concrete and clay bricks are dealt with wet finishings and a method for predicting control effect on water absorption of wet finishings is proposed. As a result, a predictive model composed of finishings, surface layer and inside of structural bodies, are clarified to be effective.