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.
The stucco finish on Arlington House, Arlington,
Virginia, was marbleized in the 1850s, approximately
30 years after it was built, but because it is a character-defining finish that has gained significance over time, it should be retained and preserved. Photo: NPS files.
Altering masonry features which are important in defining
the overall historic character of the building so that,
as a result, the character is diminished.
Replacing historic masonry features instead of repairing
or replacing only the deteriorated masonry.
Applying paint or other coatings such as stucco to
masonry that has been historically unpainted or uncoated.
Removing paint from historically painted masonry.
Changing the type of paint or coating or its color.
Stabilizing deteriorated or damaged masonry as a
preliminary measure, when necessary, prior to undertaking
appropriate preservation work.
Failing to stabilize deteriorated or damaged masonry
until additional work is undertaken, thus allowing further
damage to occur to the historic building.
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
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 existing condition of the masonry
to determine whether more than protection and maintenance
are required, that is, if repairs to 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.
The caulking shown here is not an appropriate method for repairing
cracks in historic stucco. Photo: NPS files.
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
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.
Repairing, stabilizing, and conserving fragile masonry
by using well-tested consolidants, when appropriate.
Repairs should be physically and visually compatible
and identifiable upon close inspection for future research.
Adequate protection and maintenance of a historic
building is an ongoing commitment. Here, two workers
are priming and repainting exterior stone and
wood trim. If surface treatments are neglected,
more extensive repair and replacement will be
required. Each loss further undermines a building's
historic integrity. Photo: NPS files.
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
emoving 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
Traditionally, adobe surface coatings that protected
the fragile adobe building fabric were renewed
every few years. Women are seen here recoating
an adobe wall with mud plaster mixed with straw
at Chamisal, New Mexico. Photo: Russell Lee, Farm
Security Administration Collection, Library of
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
Repairing masonry features by patching, piecing-in,
or otherwise reinforcing the masonry using recognized
preservation methods. 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 that could be stabilized, repaired
and conserved; or using untested consolidants and untrained
personnel, thus causing further damage to fragile materials.
Removing nondeteriorated mortar from sound joints,
then repointing the entire building to achieve a uniform
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.
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.
Removing masonry that could be repaired, using improper
repair techniques, or failing to document the new work.
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.
The following work
is highlighted to indicate that it represents
the greatest degree of intervention generally
recommended within the treatment Preservation,
and should only be considered after protection,
stabilization, and repair concerns have been addressed.
Limited Replacement in Kind
Replacing in kind extensively deteriorated
or missing parts of masonry features when there
are surviving prototypes such as terra-cotta brackets
or stone balusters. The new work should match
the old in material, design, color, and texture;
and be unobtrusively dated to guide future research
Replacing an entire masonry feature such as a
column or stairway when limited replacement of
deteriorated and missing parts is appropriate.
Using replacement material that does not match
the historic masonry feature; or failing to properly
document the new work.