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Historic Preservation - Technical Procedures

Spectitle:

Repointing Terra Cotta

Procedure code:

0421407R

Source:

National Capitol Region Specifications - Agriculture Bldg

Division:

Masonry

Section:

Terra Cotta Unit Masonry

Last Modified:

10/26/2012

Details:

Repointing Terra Cotta



REPOINTING TERRA COTTA


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on repointing terra
         cotta units where the mortar is deterior= ated or missing.

    B.   This procedure should be used in conjunction with 04520-
         02-R, which describes in more detail the purpose of
         repointing in general, the materials required and
         precautions that should be taken.

    C.   See 01100-07-S for general project guidelines to be
         reviewed along with this procedure. These guidelines
         cover the following sections:

         1.   Safety Precautions

         2.   Historic Structures Precaution= s

         3.   Submittals

         4.   Quality Assurance

         5.   Delivery, Storage and Handling=

         6.   Project/Site Conditions

         7.   Sequencing and Scheduling

         8.   General Protection (Surface and Surrounding)

         These guidelines should be reviewed prior to performing
         this procedure and should be followed, when applicable,
         along with recommendations from the Regional Historic
         Preservation Officer (RHPO).  

1.02 REFERENCES

    A.   American Society for Testing and Materials (ASTM)
         www.astm.org

1.03 SUBMITTALS

    A.   Product Data: Submit manufacturer's technical data for
         each product indicated including recomme= ndations for
         their application and use. Include test reports and
         certifications substantiating that produ= cts comply with
         requirements.

    B.   Restoration Program: Submit written program for each
         phase of restoration process including protection of
         surrounding materials on building and site during
         operations. Describe in detail materials, methods and
         equipment to be used for each phase of restoration work.

    C.   Protection Program: Submit for approval methods for
         protecting windows, light fixtures, decorative metal
         work, plantings, cars and landscape elements.

    D.   Samples: Submit, for verification purposes, prior to
         mock-up erection, samples of the mortar for pointing and
         masonry rebuilding and repair, in forms of 6" long by 1/2 inch
         wide sample strips of mortar set in aluminum or plastic
         channels.

1.04 QUALITY ASSURANCE

    A.   Qualifications:

         1.   Work must be performed by a firm having not less
              than five years successful experience in comparable
              masonry restoration proje= cts and employing
              personnel skilled in the restoration processes and
              operations indicated.

         2.   All technicians planned for use on the job will be
              required to successfully complete five linear feet
              of cutting and raking of mortar joints by hand in
              the presence of the Contracting Officer prior to
              working on the job. Unsuccessful performance in
              this test area will be grounds for rejection of
              this technician for this job.

    B.   Field Samples: Prior to start of general masonry restoration, prepare the following sample panels on
         building where directed by Contracting Officer. Obtain
         Contracting Officer's acceptance of visual qualities
         before proceeding with the work. Retain acceptable panels
         in undisturbed condition, suitable designated during
         construction as a standard for judging completed work.

         
1.   Repointing: Prepare two separate sample areas of
              approximately 3' high by 6' wide for each type of
              repointing required, one for demonstrating methods
              and quality of materials and workmanship expected
              in removal of mortar joints, and the other for
              demonstrating quality of materials and workmanship
              expected in pointing mortar joints.

    C.   Mock-ups:  Raking and Repointing Sample Work:

         
1.   Test/Sample Area and RHPO Approval:

              a.   Initially perform sample joint raking and
                   repointing on each of a 100 sq. ft. test of
                   terra cotta areas as approved by RHPO.

              b.   Demonstrate proficiency with joint raking
                   tools and ability to not damage masonry units
                   with hand tools.

              c.   Mix and cure test batch of repointing mortar
                   and place in joints; repeat test mix until
                   mortar color is approved.  Test mortar should
                   be matched, dried and approved before placing
                   in joints.  Sample joints should match the
                   historic in composition, color texture,
                   tooling width and other visual properties.

             
d.   Demonstrate workmanship of repointing
                   procedures and joint finishing.

              e.   Gain written approval from RHPO for test area
                   before proceeding with remaining work.

         2.   Joint Raking Method:  Rake joints by hand ONLY
              using special joint cleaning chisels and hammer.

         3.   Repointing Method:  Repoint joints by hand ONLY
              using approved pointing trowels.  NO "BAGGING" OR
              CAULKING GUN POINTING METHODS APPROVED.

   
D.   Source of Materials: Obtain materials for masonry restoration from a single source for each type of
         material required to ensure match of quality, color,
         pattern and texture.

1.05 DELIVERY, STORAGE AND HANDLING

    A.   Storage and Protection:

         1.   Protect masonry restoration materials during
              storage and construction from wetting by rain, snow
              or ground water, and from staining or intermixture
              with earth or other type materials.

         2.   Protect grout, mortar, and other materials from
              deterioration by moisture and temperature. Store in
              a dry location or on waterproof containers. Keep
              containers tightly closed and away from open
              flames. Protect liquid components from freezing.
              Comply with manufacturer's recommendations for
              minimum and maximum temperature requirements for
              storage.

1
.06 PROJECT/SITE CONDITIONS

    A.   Environmental Requirements: Do not repoint mortar joints
         or repair masonry unless air temperatures are between
         40 degress Fahrenheit (4 Celsius) and 80 degrees Fahrenheit (27 Celsius) and will remain so for at
         least 48 hours after completion of work.

1.07 SEQUENCING AND SCHEDULING

    A.   Coordinating Work: Perform masonry restoration work in
         the following sequence:

         1.   Provide approved protection of adjacent building
              materials and features.
         2.   Repair existing masonry including replacing
              existing masonry with new masonry materials.

         3.   Rake out existing mortar from deteriorated joints
              to be repointed.

         4.   Point existing mortar joints of masonry to be
              restored.

         5.   Clean up masonry surface as required after
              repointing.


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Portland Cement: ASTM C50, Type I. For stonework and
         other masonry indicated, provide non-staining white
         cement complying with staining requirements of ASTM C91
         for not more than 0.03% water soluble alkali.

    B.   Hydrated Lime: ASTM C207, Type S.

    C.   Aggregate for Mortar: ASTM C144, unless otherwise indicated.

         1.   Colored Mortar Aggregate: Natural or manufactured
              sand selection to produce mortar colors to match
              terra-cotta joints. Contracting Officer shall
              determine exact mortar color from samples prepared
              for the Contractor. Match size, texture and
              gradation of existing mortar as closely as
              possible.

    D.   Water: Clean, free of oils, acids, alkalis and organic
         matter.

    E.   Anchors: Type and size as recommended by RHPO or if not
         indicated to match existing in size and type. Fabricate
         anchors from AISI type 347 stainless steel.

2.02 MIXES

    A.   General:

         1.   Measurement and Mixing: Measure cementitious and
              aggregate material in a dry condition by volume or
              equivalent weight. Do not measure by shovel. Use
              known measure. Mix materials in a clean container,
              by hand.  See also 04100-03-S for additional
              guidance.

         2.   Mixing Pointing Mortar: Thoroughly mix cementitious
              and aggregate materials together before adding any
              water. Then mix again adding only enough water to
              produce a damp, workable mix which will retain
              its form when pressed into a ball. Maintain mortar
              in this dampened condition for 1-to-2 hours. Add
              remaining water in small portions until mortar of
              desired consistency is reached. Use mortar within
              30 minutes of final mixing; do not retemper or use
              partially hardened material.

         3.   Colored Mortar: Produce mortar of color required by
              use of selected ingredients. Do not adjust
              proportions without RHPO's approval.

         4.   Do not use admixtures of any kind in mortar, unless
              otherwise indicated.

    B.   Mortar Proportions for Terra Cotta: One part white
         Portland cement, one part lime, 6 parts mortar aggregate.

2.03 EQUIPMENT

    A.   Trowels

    B.   Hammers

    C.   Chisels

    D.   Joint tools

    E.   Plywood or steel hawk

    F.   Stiff fiber bristle brushes

    G.   Spray bottle


PART 3---EXECUTION

3.01 PREPARATION

    A.   Protection:

         1.   Protect persons, landscaping, motor vehicles, surrounding
              surfaces of building whose masonry surfaces are
              being restored, building site, and surrounding
              buildings from injury resulting from masonry
              restoration work.

         2.   Erect temporary protection covers over pedestrian
              walkways and at points of entrance and exit for
              persons and vehicles which must remain in operation
              during course of masonry restoration work.

         3.   Contractor shall test those areaway drains, window
              well drains, etc., which will be used to assure
              that drains are functioning properly prior to
              performing masonry restoration operations in those
              areas. The Contractor shall report immediately to
              the Construction Engineer the location of drains
              which are found to be stopped up or blocked.

         4.   Prevent grout or mortar used in repointing and
              repair work from staining face of surrounding
              masonry and other surfaces. Remove immediately
              grout and mortar in contact with exposed masonry
              and other surfaces.

         5.   Protect sills, ledges, windows, and projections
              from mortar droppings.

3.02 ERECTION, INSTALLATION, APPLICATION

    A.   Joint Raking:

         1.   Cut out mortar from deteriorated joints by hand to
              depths equal to 2 times their whole width but not
              less than 5/8" nor less than that required to
              expose sound, unweathered mortar.

              NOTE:  POWER OPERATED ROTARY HAND SAWS AND GRINDERS
              WILL NOT BE PERMITTED ON TERRA COTTA.

              a.   Use chisels with a 1 inch maximum head for
                   cutting out the mortar. Sharpen chisels hourly
                   to minimize the chipping. One (1) chip per linear
                   yard of cutting will be the standard of
                   acceptable skill, or as approved by the contracting officer.

              b.   Do not spall edges of masonry units or widen
                   joints. Replace any masonry units which become
                   damaged.

         2.   Rinse masonry joint surfaces with water to remove
              any dust and mortar particles. Time application of
              rinsing so that, at time of pointing, excess water
              has evaporated or run off, and joint surfaces are
              damp but free of standing water.

    B.   Joint Pointing:

         1.   Apply first layer of jointing mortar to areas where
              existing mortar was removed to depth greater than
              surrounding areas. Apply in layers not greater than
              3/8" until a uniform depth is formed. Compact each
              layer thoroughly and allow to become thumbprint-
              hard before applying next layer.

         2.   After joints have been filled to a uniform depth,
              place remaining pointing mortar in 3 layers with
              each of first and second layers filling
              approximately 2/5 of joint depth and third layer
              the remaining 1/5. Fully compact each layer and
              allow to become thumbprint hard before applying
              next layer. Take care not to spread mortar over
              edges onto exposed masonry surfaces, or to
              feather-edge mortar.

         3.   When mortar is thumbprint hard, tool to match
              original appearance of joints, unless otherwise
              indicated. Remove excess mortar from edge of joint
              by brushing.

         4.   Cure mortar by maintaining in a damp condition for
              not less than 72 hours.


3.03 ADJUSTING/CLEANING

    A.   After mortar has fully hardened, thoroughly clean exposed
         masonry surfaces of excess mortar and foreign matter
         using stiff nylon or bristle brushes and clean water,
         spray applied at low pressure.

    B.   Use of metal scrapers or brushes will not be permitted.

    C.   Use of acid or alkali cleaning agents will not be
         permitted.

                         END OF SECTION
 


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