Restoration Materials Compatible with Heritage Wall Paintings ^†

The conservation-restoration interventions at historical monuments in Romania require materials that respond both to the general requirements set out in the International Charters on the conservation and restoration of heritage, and to the specific conditions of the country: compatibility with the nature and characteristics of the constituent elements of the historical monuments, reversibility, and resistance to environmental factors. Failure to comply with the above principles has favored, in the past, the application in the works of conservation-restoration some inadequate materials, with excessive hardness and impermeability, with negative consequences on the state of preservation of historical monuments. The restoration materials presented in the paper were made on the basis of the information obtained through the physical and chemical characterization using specific investigation techniques (, X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray analysis, Fourier transform infrared spectroscopy, chemical analysis) of the mortars taken from historical monuments. The characteristics of the new materials are compared with those of other similar materials used in the restoration work.

The materials based on hydrated lime or hydraulic lime, with and without pozzolana addition have been characterized from a chemical, physical-mechanical, and durability (frost-defrost and crystallization of soluble salts resistance) point of view.

For the materials made, we obtained characteristics that recommend them in the works of conservation-restoration of the mural paintings:

• do not contain the chemical components of cement degradation (tricalcium aluminate, sulphates);
• allow the exchange of humidity, having good water vapor permeability;
• good resistance to thermal variation;
• mechanical resistance compatible with the original;
• good resistance to biodeterioration.

The materials made were tested on support-models (reproducing the original techniques) and experimentally in situ, on different masonry or wood monuments. Materials containing hydraulic lime or pozzolana addition play a special role in restoration because they allow the execution of work on monuments located under severe microclimate conditions (permanent excessive humidity or large variations in temperature and humidity).