morphology of

stone deterioration

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.

FACEWORK

MORTAR & RUBBLE

PLASTER

POINTING BEDDING MORTAR

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

CRACK AND DEFORMATION:

FRACTURE STAR CRACKS SPLITTING

CRACK AND DEFORMATION:

DEFORMATION

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

BLISTERING

BURSTING

EXFOLIATION

DELAMINATION

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

CRUMBLING SUGARING

SANDING

FRAGMENTATION

SPLINTERING

CHIPPING

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

PEELING SCALING

SPALLING

CONTOUR SCALING

FLAKING

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

Alveolization

Rounding

Differential Erosion

Erosion

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

Scratches

Impact damage

Keying

Cuts

Pitting

Microkarst

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

Efflorescence

Encrustation

Crust Discoloration

Soiling

Patina

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

Algal colonization

Lichens

Moss

Mould

Plant colonization

When planning the restoration of masonry in historic buildings, the

following principles should be considered

General Conservation Principles

Any intervention or process to be introduced should be reversible

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.

The least intervention is the best restoration