• Conservation principles: All works follow ICOMOS and UNESCO conservation principles, including minimum intervention, preservation of authenticity and original materials, compatibility, reversibility or retreatability where technically feasible, respect for the historic patina, and avoidance of conjectural reconstruction.
  • Documentation and investigation: The existing condition is recorded through photography, photogrammetry, laser scanning, material and deterioration mapping, archaeological investigation, stratigraphic testing, sampling and laboratory analysis.
  • Structural assessment: The vault, walls and structural corners are assessed using sonic testing, coring, thermography and other suitable investigations. Structural consolidation is limited to confirmed areas of need.
  • Protection and site preparation: Sacred objects are photographed, catalogued, protected or temporarily removed. Work areas, scaffolding and access routes are controlled to protect the Grotto, visitors and religious activities.
  • Cleaning: Cleaning methods are selected through trial areas. Work starts with the least aggressive dry methods, followed where necessary by controlled water-based cleaning, compresses and careful manual removal of persistent deposits.
  • Consolidation and repair: Detached plaster, stone, marble and mosaic elements are stabilised using compatible injections, lime-based mortars, grouting, anchoring or re-fixing. Incompatible previous repairs are removed only where necessary.
  • Joint and loss treatment: Open joints, cracks and lacunae are filled using compatible mortars selected for composition, strength, permeability, colour and texture. Replacement of original materials is limited to cases where conservation is not possible.
  • Aesthetic integration and protection: Chromatic reintegration is limited, distinguishable on close inspection and carried out without creating false historical evidence. Compatible protective treatments are applied only after testing and approval.
  • Building services and monitoring: Electrical, lighting, fire-protection and ventilation systems are upgraded with minimum physical and visual impact. Temperature, humidity, air quality and other environmental conditions are continuously monitored.
  • Recording and maintenance: All interventions, materials and findings are fully documented before, during and after the works. Completed areas remain subject to inspection, monitoring and planned preventive maintenance.