The exhaustive revision of previous restoration interventions is a key task when considering the real current state of conservation of an archaeological site, especially when planning new intervention project. This involves the study of former projects and reports, when possible, but also scientific analysis of effects derived from those interventions. In the particular case of archaeological sites this is not always an easy task. On one hand because there is a remarkable lack of documentation, and lack of precision on given data, more accentuated when older. On the other, because there is a poor scientific knowledge of the effects of restoration treatments in the mid- and long-term, in aspects such as durability, effectiveness or degradation mechanisms when they have become harmful. The research project presented here is deepening on the study of these effects, focusing primarily on stone material from selected archaeological sites of Merida; mainly the Roman Theatre and the House of Mitreo.