Historical buildings are subject to various environmental, physical, and human-induced factors from the time of their construction to the present day. The resulting damages and material changes are evaluated within the framework of “building pathology” in restoration science. Accurate analysis of building pathology is one of the most fundamental requirements for preserving the original identity of historical structures and passing them on to future generations.
Deteriorations observed in historical buildings are generally examined under four main categories based on their causes and symptoms:
1. Physical and Mechanical Deterioration
These types of deterioration usually result from factors such as temperature fluctuations, freeze-thaw cycles, wind effects, or foundation settlement:
- Cracks and Fissures: Caused by static stresses or dynamic effects like earthquakes. Deep fissures may indicate weaknesses in the structural system.
- Delamination and Scaling: The separation of material into layers. Moisture movements and salt crystallization trigger this process.
- Surface Powdering (Chalking): The loss of the material's binding properties, leading it to crumble into sand-like particles; this significantly reduces mechanical strength.
- Material Loss and Erosion: Volumetric losses caused by wind and physical friction, which can lead to the disappearance of architectural details.
2. Chemical Deterioration
Chemical reactions between building materials and environmental factors lead to permanent changes in the mineral structure:
- Salt Crystallization (Efflorescence): Pressure generated by dissolved salts crystallizing within pores causes internal cracking in stone.
- Carbonation and Sulphation: Atmospheric gases combining with moisture to form acidic compounds lead to the formation of "black crust" on stones like marble.
- Oxidation: Corrosion of metal elements causing volume expansion, which in turn cracks the surrounding stone texture.
3. Biological Deterioration (Biodeterioration)
Effects arising from the growth of living organisms on building surfaces:
- Microorganisms (Algae, Moss, Fungi): They alter the moisture balance, causing surface staining and microscopic levels of erosion.
- Lichen Formation: With root-like structures, they settle into stone pores and cause fragmentation on the surface.
- Plant and Root Action: The growth of plant roots settled in joints creates significant mechanical pressure on stone blocks.
4. Human-Induced Deterioration and Improper Interventions
Unconscious repair practices can accelerate the natural aging process of the structure:
- Inappropriate Cement-Based Repairs: Cement, which is incompatible with traditional lime mortars, prevents walls from "breathing" and traps moisture.
- Improper Cleaning Techniques: Methods like high-pressure sandblasting destroy the patina layer, which serves as the stone's natural protective shield.
- Incorrect Adaptive Reuse: Loading the building beyond its carrying capacity brings structural problems.
Analysis and Diagnosis: The Core Phase of Restoration
For a successful restoration application, damage analysis, mineralogical examinations, and salt analyses must be conducted in laboratory environments. Additionally, Non-Destructive Testing (NDT) methods—such as thermal imaging, ultrasonic measurements, and radar systems—provide detailed information about the internal structure of the building.