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CRUMBLING:
This condition is indicative of a certain brittleness or tendency of the
stone to break up or dissolve. It may be caused by an inherent
weakness in the limestone or gradual breakdown of the binder, or it may be
the result of external factors affecting the
strength and durability of the limestone. This condition may be caused by
the use of de-icing salts, or any other source of salt migration, such as
that which can occur when
rising damp is present. There is currently little which can be done
to repair the damage once this condition has developed, however the early
detection of potential problems and elimination of sources of salts is
critical to arresting the process. When this condition is severe and
obviously caused by the heavy or inappropriate use of de-icing salts, it
is sometimes called "Salt Fretting". Regular preservation
maintenance may eliminate the
causes promoting crumbling, however, once the condition has occurred, its
correction or repair is beyond the level of a maintenance procedure.
The Regional Historic Preservation Officer (RHPO) should be contacted for
assistance.
CHIPPING:
The separation of small pieces or larger fragments from a masonry unit,
frequently at the corners, edges or mortar joints is known as chipping.
These fractures are generally caused by deterioration and repointing,
especially due to the use of too hard a mortar, or
by accident or vandalism.
Repairs include detachment repairs, patching and splicing. Repair of
chipped stone requires a skilled mason and is not a maintenance procedure.
If chipping is due to occasional impact from mowing or other landscape
maintenance, steps should be taken to prevent future damage.
CRACKING:
This condition is manifested by the appearance of narrow fissures ranging
from less than 1/16 to 1/2 inch wide or more in the stone. It results from
a variety of causes, such as structural overloading due to settlement, the
use of too hard a mortar mix or a flaw in
the material. Minor cracking may be no problem, in and of itself,
but it can be an indication of structural problems and the cracks can be a
point of entry of water into the interior of the stone, promoting salt
migration. Cracking, which allows water or salts to
enter the stone, increases the possibility of failure along the limestone
and may result in subsequent spalling. Repairs include patching and
replacement.
DETACHMENT:
This is not a failure of the material per se but a failure of the
construction system, i.e. the connectors and/or joints. The
definition implies that the failed component survives intact and may be
re-installed using appropriate mechanical techniques.
The failure of anchors or metal connectors which lead to detachment may be
caused and/or accelerated by the penetration of water into the structure
behind the stone, causing rust and corrosion. Adequate pointing and
caulking can prevent leakage and penetration of water into the
system.
EFFLORESCENCE:
The appearance of a whitish deposit locally or uniformly over the surface
may be efflorescence, the surface deposition of soluble salts. There
are numerous sources for the soluble salts which create the hazy
appearance; salts can come from mortar, improper cleaning agents, rising
damp, de-icing salts, chemical landscaping treatments and air pollution.
Efflorescence can be a salt residue resulting from improper chemical
cleaning, i.e. too strong a chemical cleaner or inadequate rinsing.
It can also be an indication of water problems. Salt migration and/or
sub-florescence and efflorescence should be considered a symptom which
should be investigated to identify the source of the soluble salts and/or
the source of moisture. Corrective action should then be taken to
eliminate the source of the problem once it is identified.
Some efflorescence may occur naturally with new stones, mortar and
installation materials. Normally, this efflorescence will be removed
by natural rain and weathering processes and/or by regular washing.
The new or continued appearance of efflorescence is a stronger indicator
of problems like rising damp or inappropriate cleaning methods, all of
which should be referred to the Regional Historic Preservation Officer (RHPO).
EROSION:
Erosion is the wearing away of the material surface by the natural action
of wind, windblown particles and water. It can occur with limestone
as well as any exposed materials. Inspections should include examination
for any apparent loss of detail and edge sharpness which could be due to
erosion.
Erosion may be less of a problem on rock-faced or quarry-faced marble, but
may be a more serious problem on stone with more precise detail.
Little can be done to correct this problem once it occurs, other than to
protect the surface from further exposure.
This may stop or at least retard the erosion process.
FLAKING:
This is an early stage of peeling, exfoliation, delamination or spalling
evidenced by the detachment of small flat thin pieces of the outer layers
of stone from a larger piece of stone. Flaking is usually caused by
capillary moisture or freeze-thaw cycles which
occur within the masonry. The problem can also occur due to
sub-florescence, so that if flaking occurs, the area should be examined to
determine if salt crystallization is occurring in the flaked areas.
PEELING:
Peeling is the flaking away of the stone surface from the substrate in
strips or layers. It may result from the improper application of
masonry coatings which result in failure of the coating and/or stone
surface. It may also result from a defect in the stone, or
from weathering. Encrustations
of the surface caused by chemical reactions with environmental elements
may also peel or flake along the bedding plane.
RISING DAMP:
Rising damp is the suction of ground water into the base of masonry
through capillary action. Moisture is drawn up into the stone and
may rise and fall due to conditions of temperature; humidity; site
grading; absence or failure of damp courses, and/or treatments to the
masonry surfaces which affect evaporation.
During active wet periods, rising damp may be visible as a darkening of
the stone along the base at ground level. Due to the continuous
changing of the moisture level due to varying exposure conditions,
staining or efflorescence may be visible at a range of
several feet up from the ground. Continuation of the problem can lead
to more severe problems of flaking, peeling and/or spalling, but the
correction of the problem requires the elimination of the source of water
or the interruption of its path into the stone by
physical or chemical damp-proofing.
SPALLING:
Spalling is the separation and breaking away of pieces of stone due to
sub-florescence, freeze-thaw, improper repointing with too hard a
mortar mix or portland cement, or structural overloading of the stone.
Spalling is less frequent with limestone than with sedimentary stones
which are also less hard. Limestone is hard enough to resist
internal forces which would cause spalling in other natural stones or
fabricated masonry.
SUB-FLORESCENCE:
This is a potentially harmful internal accumulation of soluble salts
deposited under or just beneath the masonry surface as moisture in the
wall evaporates.
The build-up of salts and their crystallization can create substantial
pressures within the masonry, causing pieces to break off along the planes
of deposition. Efflorescence at the surface is an indication that
sub-florescence is possible. Techniques for mitigating the problem
include poulticing, removal of identified salt sources, elimination of
moisture in the stone and damp-proofing.
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