Historic Preservation - Technical Procedures
- Guidelines For Rehabilitating Historic Buildings: Masonry
- Procedure code:
- National Park Service, Preservation Assistance Division
- General Requirements
- Reference Standards
- Last Modified:
- Guidelines For Rehabilitating Historic Buildings: Masonry
- Last Modified:
GUIDELINES FOR REHABILITATING HISTORIC BUILDINGS: MASONRY
U.S. Department of the Interior
National Park Service
Preservation Assistance Division
An illustrated booklet addressing the Secretary's Standards and the
guidelines is available from the U.S. Government Printing Office.
The title is "The Secretary of the Interior's Standards for
Rehabilitation & Illustrated Guidelines for Rehabilitating Historic
Buildings", ISBN 0-16-035979-1.
Each of the guidelines included in the booklet mentioned above have
been separated into individual entries for specific use in HBPP.
This entry represents one of many guidelines included in the
booklet and describes RECOMMENDED and NOT RECOMMENDED applications
of the Secretary of the Interior's Standards as they relate to
Masonry. For a list of the Secretary of the Interior's Standards
for Rehabilitation, see 01091-04-S; For general information
relating to the purpose, organization and content of the individual
guidelines, see 01091-05-S. Both of these entries should be
referenced along with the information contained in this document.
MASONRY: Brick stone, terra cotta, concrete, adobe, stucco and
Masonry features (such as brick cornices and door pediments, stone
window architraves, terra cotta brackets and railings) as well as
masonry surfaces (modelling, tooling, bonding patterns, joint size,
and color) may be important in defining the historic character of
the building. It should be noted that while masonry is among the
most durable of historic building materials, it is also the most
susceptible to damage by improper maintenance or repair techniques
and by harsh or abrasive cleaning methods. Most preservation
guidance on masonry thus focuses on such concerns as cleaning and
the process or repointing.
IDENTIFYING, RETAINING AND PRESERVING
- 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 joint and unit size, tooling and
bonding patterns, coatings, and color.
- 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
- 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
PROTECTING AND MAINTAINING
- Protecting and maintaining masonry by providing proper
drainage so that water does not stand on flat, horizontal
surfaces or accumulate in curved decorative features.
- 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 only when necessary to halt
deterioration or remove heavy soiling.
- Cleaning masonry surfaces when they are not heavily
soiled to create a new appearance, thus needlessly
introducing chemicals or moisture into historic
- Carrying out masonry surface cleaning tests after it has
been determined that such cleaning is necessary. Tests
should be observed over a sufficient period of time so
that both the immediate effects ad the long-range effects
are known to enable selection of the gentlest method
- Cleaning masonry surfaces without testing or without
sufficient time for the testing results to be of value.
- Cleaning masonry surfaces with the gentlest method
possible, such as low pressure water and detergents,
using natural bristle brushes.
- 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
- 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 mortar joints.
- Inspecting painted masonry surfaces to determine whether
repainting is necessary.
- Removing paint that is firmly adhering to, and thus
protecting, masonry surfaces.
- Removing damaged or deteriorated paint only to the next
sound layer using the gentlest method possible (e.g.,
handscraping) prior to repainting.
- Using methods of removing paint which are destructive to
masonry, such as sandblasting, application of caustic
solutions, or high pressure waterblasting.
- Applying compatible paint coating systems following
proper surface preparation.
- Failing to follow manufacturers' product and application
instructions when repainting masonry.
- Repainting with colors that are historically appropriate
to the building and district.
- Using new paint colors that are inappropriate to the
historic 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 undertake adequate measures to assure the
preservation of masonry features.
- 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
- Removing nondeteriorated mortar from sound joints, then
repointing the entire building to achieve a uniform
- Removing deteriorated mortar by carefully hand-raking the
joints to avoid damaging the masonry.
- Using electric saws and hammers rather than hand tools to
remove deteriorated mortar from joints prior to
- Duplicating old mortar in strength, composition, color,
- 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.
- Duplicating old mortar joints in width and in joint
- Changing the width or joint profile when repointing.
- Repairing stucco by removing the damaged material and
patching with new stucco that duplicates the old in
strength, composition, color, and texture.
- Removing sound stucco; or repairing with new stucco that
is stronger than the historic material or does not convey
the same visual appearance.
- Using mud plaster as a surface coating over unfired,
unstabilized adobe because the mud plaster will bond to
- 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.
- 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.
- Replacing an entire masonry feature such as a cornice or
balustrade when repair of the masonry and limited
replacement of deteriorated or missing parts are
- 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
- 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
- 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.
- 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
to guide the new work. 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.
NOTE: THE FOLLOWING REPRESENTS PARTICULARLY COMPLEX TECHNICAL OR
DESIGN ASPECTS OF REHABILITATION PROJECTS AND SHOULD ONLY BE
CONSIDERED AFTER THE PRESERVATION CONCERNS LISTED ABOVE HAVE BEEN
DESIGN FOR 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.
END OF SECTION