2 nd Historic Mortars Conference HMC2010 and RILEM TC 203-RHM Final Workshop 22-24 September 2010, Prague, Czech Republic 527 II.13 Analytical Diagnosis Protocol to Assess the Impacts of Environmental Stressors on Historical Mortars Acting as the Support of Wall Paintings Maite Maguregui 1 , Ulla Knuutinen 2 , Kepa Castro 1 , Irantzu Martinez- Arkarazo 1 and Juan Manuel Madariaga 1 1 University of the Basque Country, Department of Analytical Chemistry, Spain, maite.maguregui@ehu.es 2 Helsinki Metropolia University of Applied Sciences, Finland Abstract This work describes a new analytical diagnosis protocol to assess the environmental impacts on historical mortars acting as supports of wall paintings. The adequate assessment of such impacts requires not only the identification of the original and decaying products but also clarify the mechanisms (chemical reactions between original materials and environmental stressors) that promote the decaying. The proposed protocol is divided in four steps: (1) Analytical (both elemental and molecular) characterization by means of portable non-destructive spectroscopic and micro-destructive analytical techniques to identify the original and decaying compounds of the mortars, (2) Chemometric analysis on quantitative data of soluble salts, (3) Chemical simulations (MEDUSA, RUNSALT…) to explain the reactions between mortar components and environmental stressors and (4) Validation of the decaying reaction taking into account the agreement between the spectroscopic information and the chemometric calculation + chemical simulation results. The possibilities offered by this diagnosis protocol are described on two case studies: (a) mortars from medieval wall painting affected by ammonium nitrate rich infiltration waters and (b) Pompeian mortars of wall paintings exposed outdoors from the last 150 years after its excavations. 1 Introduction A mural or wall painting is the general term for a painting applied directly to a wall. The mortar of a wall painting is composed of two layers, the arriccio layer