Identify, Retain and Preserve
Identifying, retaining, and preserving masonry features
that are important in defining the overall historic
character of the building such as walls, brackets, railings,
cornices, window architraves, door pediments, steps,
and columns; and details such as tooling and bonding
patterns, coatings, and color.
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The variety and arrangement of the materials
is important in defining the historic character,
starting with the large pieces of broken stone
which form the projecting base for the building
walls, then changing to a wall of roughly rectangular
stones which vary in size, color, and texture,
all with projecting beaded mortar joints.
Changing the raised mortar joints, for example,
would drastically alter the character. Photo: NPS files.
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Removing or radically changing masonry features which
are important in defining the overall historic character
of the building so that, as a result, the character
is diminished.
Replacing or rebuilding a major portion of exterior
masonry walls that could be repaired so that, as a result,
the building is no longer historic and is essentially
new construction.
Applying paint or other coatings such as stucco to
masonry that has been historically unpainted or uncoated
to create a new appearance.
Removing paint from historically painted masonry.
Radically changing the type of paint or coating or
its color.
Protect and Maintain
Protecting and maintaining masonry by providing proper
drainage so that water does not stand on flat, horizontal
surfaces or accumulate in curved decorative features.
Cleaning masonry only when necessary to halt deterioration
or remove heavy soiling.
Carrying out masonry surface cleaning tests after
it has been determined that such cleaning is appropriate.
Tests should be observed over a sufficient period of
time so that both the immediate and the long range effects
are known to enable selection of the gentlest method
possible.
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The iron stain on this granite post may be removed
by applying a commercial rust-removal product
in a poultice. Photo: NPS files.
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Cleaning masonry surfaces with the gentlest method
possible, such as low pressure water and detergents,
using natural bristle brushes.
Inspecting painted masonry surfaces to determine
whether repainting is necessary.
Removing damaged or deteriorated paint only to the
next sound layer using the gentlest method possible
(e.g., handscraping) prior to repainting.
Applying compatible paint coating systems following
proper surface preparation.
Repainting with colors that are historically appropriate
to the building and district.
Evaluating the overall condition of the masonry
to determine whether more than protection and maintenance
are required, that is, if repairs to the masonry features
will be necessary.
Failing to evaluate and treat the various causes of
mortar joint deterioration such as leaking roofs or
gutters, differential settlement of the building, capillary
action, or extreme weather exposure.
Cleaning masonry surfaces when they are not heavily
soiled to create a new appearance, thus needlessly introducing
chemicals or moisture into historic materials.
Cleaning masonry surfaces without testing or without
sufficient time for the testing results to be of value.
Historic brick damaged by sandblasting.
Sandblasting brick or stone surfaces using dry or wet
grit or other abrasives. These methods of cleaning permanently
erode the surface of the material and accelerate deterioration.
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Abrasive cleaning methods include all techniques that
physically abrade the building surface to remove soils,
discolorations or coatings. Sandblasting has permanently damaged this brick
wall. Photo: NPS files
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Using a cleaning method that involves water or liquid
chemical solutions when there is any possibility of
freezing temperatures.
Cleaning with chemical products that will damage masonry,
such as using acid on limestone or marble, or leaving
chemicals on masonry surfaces.
Applying high pressure water cleaning methods that
will damage historic masonry and the mortar joints.
Removing paint that is firmly adhering to, and thus
protecting, masonry surfaces.
Using methods of removing paint which are destructive
to masonry, such as sandblasting, application of caustic
solutions, or high pressure waterblasting.
Failing to follow manufacturers' product and application
instructions when repainting masonry.
Using new paint colors that are inappropriate to the
historic building and district.
Failing to undertake adequate measures to assure the
protection of masonry features.
Repair
Repairing masonry walls and other masonry features
by repointing the mortar joints where there is evidence
of deterioration such as disintegrating mortar, cracks
in mortar joints, loose bricks, damp walls, or damaged
plasterwork.
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Mortars for repointing should be softer or more permeable than the masonry units and no
harder or more impermeable than the historic mortar to prevent damage to the masonry
units. This early 19th century building is being repointed
with lime mortar. Photo: John P. Speweik.
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Removing deteriorated mortar by carefully hand-raking
the joints to avoid damaging the masonry.
Duplicating old mortar in strength, composition,
color, and texture.
Duplicating old mortar joints in width and in joint
profile.
Repairing stucco by removing the damaged material
and patching with new stucco that duplicates the old
in strength, composition, color, and texture.
Using mud plaster as a surface coating over unfired,
unstabilized adobe because the mud plaster will bond
to the adobe.
Cutting damaged concrete back to remove the source
of deterioration (often corrosion on metal reinforcement
bars). The new patch must be applied carefully so it
will bond satisfactorily with, and match, the historic
concrete. Replacement stones tooled to match original.
Repairing masonry features by patching, piecing-in,
or consolidating the masonry using recognized preservation
methods. Repair may also include the limited replacement
in kind--or with compatible substitute material--of
those extensively deteriorated or missing parts of masonry
features when there are surviving prototypes such as
terra-cotta brackets or stone balusters.
Applying new or non-historic surface treatments
such as water-repellent coatings to masonry only after
repointing and only if masonry repairs have failed to
arrest water penetration problems.
Removing nondeteriorated mortar from sound joints, then
repointing the entire building to achieve a uniform
appearance.
Using electric saws and hammers rather than hand tools
to remove deteriorated mortar from joints prior to repointing.
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Some aspects of a building's visual character
are fragile and are easily lost. This is true
of brickwork, for example, which can be irreversibly
damaged with inappropriate cleaning techniques
or by insensitive repointing practices. The historic
character of this front wall is being dramatically
changed from a wall where the bricks predominate,
to a wall that is visually dominated by the mortar
joints. Photo: NPS files.
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Repointing with mortar of high portland cement content
(unless it is the content of the historic mortar). This
can often create a bond that is stronger than the historic
material and can cause damage as a result of the differing
coefficient of expansion and the differing porosity
of the material and the mortar.
Repointing with a synthetic caulking compound. Using
a "scrub" coating technique to repoint instead of traditional
repointing methods.
Changing the width or joint profile when repointing.
Removing sound stucco; or repairing with new stucco
that is stronger than the historic material or does
not convey the same visual appearance.
Applying cement stucco to unfired, unstabilized adobe.
Because the cement stucco will not bond properly, moisture
can become entrapped between materials, resulting in
accelerated deterioration of the adobe.
Patching concrete without removing the source of deterioration.
Replacing an entire masonry feature such as a cornice
or balustrade when repair of the masonry and limited
replacement of deteriorated of missing parts are appropriate.
Using a substitute material for the replacement part
that does not convey the visual appearance of the surviving
parts of the masonry feature or that is physically or
chemically incompatible.
Applying waterproof, water repellent, or non-historic
coatings such as stucco to masonry as a substitute for
repointing and masonry repairs. Coatings are frequently
unnecessary, expensive, and may change the appearance
of historic masonry as well as accelerate its deterioration.
Replace
Replacing in kind an entire masonry feature that
is too deteriorated to repair--if the overall form and
detailing are still evident--using the physical evidence
as a model to reproduce the feature. Examples can include
large sections of a wall, a cornice, balustrade, column,
or stairway. If using the same kind of material is not
technically or economically feasible, then a compatible
substitute material may be considered.
Removing a masonry feature that is unrepairable and
not replacing it; or replacing it with a new feature
that does not convey the same visual appearance.
The following work
is highlighted to indicate that it represents
the particularly complex technical or design aspects
of Rehabilitation projects and should only be
considered after the preservation concerns listed
above have been addressed.
Design for the Replacement of Missing Historic
Features
Designing and installing a new masonry feature
such as steps or a door pediment when the historic
feature is completely missing. It may be an accurate
restoration using historical, pictorial, and physical
documentation; or be a new design that is compatible
with the size, scale, material, and color of the
historic building.
Creating a false historical appearance because
the replaced masonry feature is based on insufficient
historical, pictorial, and physical documentation.
Introducing a new masonry feature that is incompatible
in size, scale, material and color.
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