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Natural Causes • rain and water action • ground movements • thermal stresses • vegetation and root damage • rodent activity • wind erosion
Human Causes • neglect • quarrying or robbing • fire • vandalism and war • mistreatment of structure • design inadequacies
Stone is defined as rock selected or processed by shaping, cutting or sizing for building or other use. Masonry will refer to man-made works or structures composed of stone or brick, including the mortars, joints, plasters and renders therein.
This type of weathering is caused by factors such as vibrations,
ground movements, materials expansion, temperature changes
and extremes, and frost and salt bursting.
Mechanical weathering
Causes of Stone Deterioration
Causes of Stone Deterioration
This includes reactions to processes like oxidation,
chemical dissolution, photochemical processes and precipitation of dust,
acids and gases. Efflorescence or the
presence of salts and black crust formations on stones
is a form of chemical weathering.
Chemical weathering
Causes of Stone Deterioration
This weathering includes vegetal and
microorganism metabolism and growth,
erosion, and root cracking. Animal and human abuse, misuse and neglect are also
factors for this weathering type.
Biogenic weathering
In the absence of an existing local standard or reference to identify morphologies of stone alteration and deterioration,
it is recommended that the internationally accepted NORMAL reference be used for local conditions.
Or the
Alteration modification of the material that does not necessarily imply a negative change to its characteristics from the conservation point of view. . For instance, a reversible coating applied on a stone may be considered as an alteration.
Deterioration modification of the material which always implies a decline in its characteristics from the conservation point of view. Also, process of making or becoming worse or lower in quality, value, character, etc...; depreciation.
Damage Human perception of the loss of value due to decay.
Decay Any chemical or physical modification of the intrinsic stone properties leading to a loss of value or to the impairment of use.
Weathering Any chemical or mechanical process by which stones exposed to the weather undergo changes
in character and deteriorate.
Degradation decline in condition, quality, or functional
capacity.
External Agents • Changes in
temperature • Humidity • Precipitation of
dust, acids and gases
• Movements in the ground
• Vibrations • Catastrophic events • Organisms that
grow outside the stone material
Internal Agents • Humidity in the
material • Salts • Incompatible
materials like iron, wood, etc.
• Organisms that grow or penetrate inside the stone material
CRACKS: • Visible individual cracks resulting in the
separation of one part to another
SUBTYPES: 1. Fractures - – crack that crosses
completely through the stone 2. Star Crack - due to corrosion or impact 3. Hair Crack 4. Splitting - fractures along the planes of
weakness (micro cracks and clay/silt layers
DEFORMATION: • Change in shape without losing integrity of
leading to bending, buckling or twisting of stone
DEFORMATION: • Change in shape without losing integrity of
leading to bending, buckling or twisting of stone
DETACHMENT: SUBTYPES:
1. Blistering – air filled, raised elevations on the face of stone resulting in detachment of outer layer
2. Bursting - loss of stone surface from internal pressure forming a crater
3. Delamination - physical separation into one or several layers
a. Exfoliation - detachment of multiple stone layers sub-parallel
4. Disintegration – detachment of single grains or aggregates of grains
a. crumbling - < 2cm b. granular disintegration –
sanding, powdering and sugaring 5. Fragmentation – complete of partial
breaking up of stone into variable dimensions that are irregular in form, thickness and volume. a. splintering - granular disintegration of
sandstones and granites
b. chipping - granular disintegration of marble
6. Peeling - shedding, coming off or partial detachment of a superficial layer having the aspect of a film or coating which has been applied on the stone surface
7. Scaling - detachment of stone as a scale or stack of scales not following the stone structure and detaching a. Flaking – sandstone contaminated with
sodium chloride; salt crystallization induces granular disintegration
b. Contour scaling – thin detachments on face and figure
c. Spalling – flat dimension stones
FEATURES INDUCED BY MATERIAL LOSS:
SUBTYPES: 1. Alveolization – formation of surface cavities
a. Coving – erosion of alveole developing on the edge of the block
2. Erosion – loss of original surface leading to smooth shapes a. Rounding – preferential erosion leading to
round edges b. Roughening - selective loss of small
particles from an originally smooth surface
3. Mechanical damage - loss of stone material due to mechanical action a. Impact damage - b. Cut – c. Scratch – d. Abrasion – wearing down by friction e. Keying – impact damage that will assist the
adhesion of an added material 4. Microkarst – small interconnected depressions
caused by dissolution of calcareous stone surface 5. Missing part – empty space 6. Perforation – surface punctures 7. Pitting – shallow cavities, cylindrical or conical
which are not interconnected
DISCOLORATION AND DEPOSIT: SUBTYPES:
1. Crust – accumulation of materials on the surface 2. Discoloration - change in color
a. Coloration – b. Staining – ex. Iron staining
3. Efflorescence – whitish powdery surface 4. Encrustation – hard, mineral outer layer
adhering to the stone 5. Film – coating of a clear layer 6. Graffiti – 7. Patina - chromatic alteration due to natural or
artificial aging 8. Soiling – ex. soot
BIOLOGICAL COLONIZATION: • colonization by symbiosis
SUBTYPES: 1. Algae – microscopic vegetal organisms 2. Lichen – leathery appearance 3. Moss - 4. Mould – microscopic fungus 5. Plant – tree, ferns, herbs
When planning the restoration of masonry in historic buildings, the
following principles should be considered
General Conservation Principles
Any new addition or change must always refer to the existing structure. Any intervention
planned must be supported with tests in the laboratory or in situ.
When introducing new materials or processes into the old, the new must match the strength of, or be slightly
weaker than the old.