Identify, Retain and Preserve
Identifying, retaining, and preserving masonry features
from the restoration period 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 craft details reflect the building's period
of significance and thus need to be carefully
preserved. This artisanry would be difficult to
match if it were damaged, and the effect could
be easily damaged through insensitive treatments
such as painting the brickwork or by careless
repointing. Photo: NPS files.
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Altering masonry features from the restoration period.Failing
to properly document masonry features from the restoration
period which may result in their loss.Applying paint
or other coatings such as stucco to masonry or removing
paint or stucco from masonry if such treatments cannot
be documented to the restoration period.Changing the
type or color of the paint or coating unless the work
can be substantiated by historical documentation.
Protect and Maintain
Protecting and maintaining masonry from the restoration
period 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.
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.
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Because there are so many possible causes for
deterioration in historic buildings, it may be
desirable to retain a consultant, such as a historic
architect or architectural conservator, to analyze
the building. This late 19th century granite has
recently been repointed with the joint profile
and mortar color carefully matched to the original.
Photo: NPS files.
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Repainting with colors that are documented to the
restoration period of the building.
Evaluating the existing condition of the masonry
to determine whether more than protection and maintenance
are required, that is, if repairs to the masonry features
from the restoration period 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, 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.
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.
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 not documented to the
restoration period of the building.
Failing to undertake adequate measures to assure the
protection of masonry features from the restoration
period.
Repair
Repairing, stabilizing and conserving fragile masonry
from the restoration period by well-tested consolidants,
when appropriate. Repairs should be physically and visually
compatible and identifiable upon close inspection for
future research.
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"Fallingwater," a dramatic reinforced
concrete residence by Frank Lloyd Wright, is anchored
into bedrock on the hillside. The
significance of this structure means great attention
to detail must be taken during stabilization and repair work on the deteriorating concrete features. Photo: HABS Collection, NPS.
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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.
Removing deteriorated mortar by carefully hand-raking
the joints to avoid damaging the masonry. Duplicating,
and if necessary, reproducing period mortar in strength,
composition, color, and texture.
Duplicating and, if necessary, reproducing period
mortar joints in width and in joint profile.
Repairing stucco by removing the damaged material
and patching with new stucco that duplicates stucco
of the restoration period 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.
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This 18th century pediment and surrounding wall
exhibit distinctively different mortar joints.
These differences need to be taken into consideration
in a restoration project. Photo: NPS files.
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Repairing masonry features from the restoration
period by patching, piecing-in, or otherwise reinforcing
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 from
the restoration period when there are surviving prototypes
such as terra-cotta brackets or stone balusters. The
new work should be unobtrusively dated to guide future
research and treatment.
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 masonry from the restoration period that could
be stabilized, repaired and conserved; or using untested
consolidants and untrained personnel, thus causing further
damage to fragile historic materials.
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.
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.
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Caulking was inappropriately used here in place
of mortar on the top of the wall. As a result,
it has not been durable. Photo: NPS files.
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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 from the restoration
period such as a cornice or balustrade when repair of
the masonry and limited replacement of deteriorated
or 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 from
the restoration period 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.
The new work should be unobtrusively dated to guide
future research and treatment.
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The Rhode Island State House (left), designed by McKim, Mead, & White, is undergoing restoration of the marble terraces (right), walls, steps, balustrades and plazas in a phased project. Photos: Durkee, Brown, Viveiros
& Werenfels, Architects.
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Removing a masonry feature from the restoration period
that is unrepairable and not replacing it.
The following Restoration
work is highlighted to indicate that it involves
the removal or alteration of existing historic
masonry features that would be retained in Preservation
and Rehabilitation treatments; and the replacement
of missing masonry features from the restoration
period using all new materials.
Removing Existing Features from Other Historic
Periods
Removing or altering masonry features from
other historic periods such as a later doorway,
porch, or steps.
Documenting materials and features dating
from other periods prior to their alteration or
removal. If possible, selected examples of these
features or materials should be stored to facilitate
future research.
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The treatment, Restoration, is undertaken
to return a building to its appearance at
a specific time, as shown in this drawing.
The Meyer May House in Grand Rapids, Michigan,
was designed by Frank Lloyd Wright and built
in 1909. In 1922, May added to the house
for an expanding family. After the May occupancy,
the house was altered for use as apartments,
with a carport added in 1955. In the 1980s
restoration, the Wright's original design
was deemed more significant than May's later
changes, and, as a result, the additions
were removed and the house returned to its
1909 appearance. Drawing: Martha L. Werenfels,
AIA.
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Failing to remove a masonry feature from another
period, thus confusing the depiction of the building's
significance.
Failing to document masonry features from other
historic periods that are removed from the building
so that a valuable portion of the historic record
is lost.
Re-creating Missing Features
from the Restoration Period
Re-creating a missing masonry feature that
existed during the restoration period based on
physical or documentary evidence; for example,
duplicating a terra-cotta bracket or stone balustrade.
Constructing a masonry feature that was part of
the original design for the building but was never
actually built; or constructing a feature which
was thought to have existed during the restoration
period, but for which there is insufficient documentation.
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