Skip to main content

Historic Preservation - Technical Procedures

Spectitle:

Guidelines For Rehabilitating Historic Buildings: Masonry

Procedure code:

0109106S

Source:

National Park Service, Preservation Assistance Division

Division:

General Requirements

Section:

Reference Standards

Last Modified:

02/24/2012

Details:

Guidelines For Rehabilitating Historic Buildings: Masonry



GUIDELINES FOR REHABILITATING HISTORIC BUILDINGS:  MASONRY


U.S. Department of the Interior
National Park Service
Preservation Assistance Division
Washington, D.C.


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.


BUILDING EXTERIOR

MASONRY:  Brick stone, terra cotta, concrete, adobe, stucco and
mortar

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

1.   Recommended:

    -    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.

    Not Recommended:

    -    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.  


PROTECTING AND MAINTAINING

1.   Recommended:

    -    Protecting and maintaining masonry by providing proper
         drainage so that water does not stand on flat, horizontal
         surfaces or  accumulate in curved decorative features.

    Not Recommended:

    -    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.

2.   Recommended:

    -    Cleaning masonry only when necessary to halt
         deterioration or remove heavy soiling.

    Not Recommended:

    -    Cleaning masonry surfaces when they are not heavily
         soiled to create a new appearance, thus needlessly
         introducing chemicals or moisture into historic
         materials.

3.   Recommended:

    -    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
         possible.

    Not Recommended:

    -    Cleaning masonry surfaces without testing or without
         sufficient time for the testing results to be of value.





4.   Recommended:

    -    Cleaning masonry surfaces with the gentlest method
         possible, such as low pressure water and detergents,
         using natural bristle brushes.

    Not Recommended:

    -    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 mortar joints.

5.   Recommended:

    -    Inspecting painted masonry surfaces to determine whether
         repainting is necessary.

    Not Recommended:

    -    Removing paint that is firmly adhering to, and thus
         protecting, masonry surfaces.

6.   Recommended:

    -    Removing damaged or deteriorated paint only to the next
         sound layer using the gentlest method possible (e.g.,
         handscraping) prior to repainting.


    Not Recommended:

    -    Using methods of removing paint which are destructive to
         masonry, such as sandblasting, application of caustic
         solutions, or high pressure waterblasting.

7.   Recommended:

    -    Applying compatible paint coating systems following
         proper surface preparation.

    Not Recommended:

    -    Failing to follow manufacturers' product and application
         instructions when repainting masonry.

8.   Recommended:

    -    Repainting with colors that are historically appropriate
         to the building and district.

    Not Recommended:

    -    Using new paint colors that are inappropriate to the
         historic building and district.

9.   Recommended:

    -    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.

    Not Recommended:

    -    Failing to undertake adequate measures to assure the
         preservation of masonry features.


REPAIRING

1.   Recommended:

    -    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.

    Not Recommended:

    -    Removing nondeteriorated mortar from sound joints, then
         repointing the entire building to achieve a uniform
         appearance.

2.   Recommended:

    -    Removing deteriorated mortar by carefully hand-raking the
         joints to avoid damaging the masonry.

    Not Recommended:

    -    Using electric saws and hammers rather than hand tools to
         remove deteriorated mortar from joints prior to
         repointing.

3.   Recommended:

    -    Duplicating old mortar in strength, composition, color,
         and texture.

    Not Recommended:

    -    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.

4.   Recommended:

    -    Duplicating old mortar joints in width and in joint
         profile.

    Not Recommended:

    -    Changing the width or joint profile when repointing.

5.   Recommended:

    -    Repairing stucco by removing the damaged material and
         patching with new stucco that duplicates the old in
         strength, composition, color, and texture.

    Not Recommended:

    -    Removing sound stucco; or repairing with new stucco that
         is stronger than the historic material or does not convey
         the same visual appearance.

6.   Recommended:

    -    Using mud plaster as a surface coating over unfired,
         unstabilized adobe because the mud plaster will bond to
         the adobe.

    Not Recommended:

    -    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.

7.   Recommended:

    -    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.

    Not Recommended:

    -    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
         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.

8.   Recommended:

    -    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.

    Not Recommended:

    -    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

1.   Recommended:

    -    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.

    Not Recommended:

    -    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
ADDRESSED.

DESIGN FOR MISSING HISTORIC FEATURES

1.   Recommended:

    -    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.

    Not Recommended:

    -    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