The validity of an equation which predicts the behavior of a porous solid in contact with an acid or buffered acid solution is demonstrated. The results indicate that dissolution of the solid will occur followed by reprecipitation in the pores ahead of the advancing acid. In a buffered acid solution, dissolution occurs at the front of the advancing acid, reprecipitation ahead of this and surprisingly, dissolution also occurs further ahead in front of the precipitation front. This phenomenon is compared to that observed in tooth decay and it is concluded that other equally interesting implications of this analysis exist, such as the corrosion of masonry. In fact the work appears relevant to innumerable observations of this kind in stone conservation. -- AATA