Repointing Terra Cotta

Procedure code:
421407S
Source:
National Capitol Region Specifications - Agriculture Bldg
Division:
Masonry
Section:
Terra Cotta Unit Masonry
Last Modified:
04/17/2017

PART 1---GENERAL

1.01 SUMMARY

  1. This procedure includes guidance on repointing terra cotta units where the mortar is deterior= ated or missing.
  2.  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.
  3. 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 Precautions
    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

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

1.03 SUBMITTALS

  1.  Product Data: Submit manufacturer's technical data for each product indicated including recommendations for their application and use. Include test reports and certifications substantiating that products comply with requirements.
  2.  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.
  3. Protection Program: Submit for approval methods for protecting windows, light fixtures, decorative metal work, plantings, cars and landscape elements.
  4. 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

  1. Qualifications:
    1.  Work must be performed by a firm having not less than five years successful experience in comparable masonry restoration projects 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.
  2. 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.
  3. Mock-ups: Raking and Repointing Sample Work:
    1. Test/Sample Area and RHPO Approval:
      1. Initially perform sample joint raking and repointing on each of a 100 sq. ft. test of terra cotta areas as approved by RHPO.
      2. Demonstrate proficiency with joint raking tools and ability to not damage masonry units with hand tools.
      3. 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.
      4.  Demonstrate workmanship of repointing procedures and joint finishing.
      5. 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.
  4. 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

  1. 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.m Comply with manufacturer's recommendations for minimum and maximum temperature requirements for storage.

1.06 PROJECT/SITE CONDITIONS

  1. 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

  1.  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

  1.  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.
  2. Hydrated Lime: ASTM C207, Type S.
  3. 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.
  4. Water: Clean, free of oils, acids, alkalis and organic matter.
  5. 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

  1. 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.
  2. Mortar Proportions for Terra Cotta: One part white Portland cement, one part lime, 6 parts mortar aggregate.

2.03 EQUIPMENT

  1. Trowels
  2. Hammers
  3. Chisels
  4. Joint tools
  5. Plywood or steel hawk
  6. Stiff fiber bristle brushes
  7. Spray bottle

PART 3---EXECUTION

3.01 PREPARATION

  1. 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

  1.  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.
      1. 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.
      2.  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.
  2. 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

  1. 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.
  2. Use of metal scrapers or brushes will not be permitted.
  3. Use of acid or alkali cleaning agents will not be permitted.

END OF SECTION

Last Reviewed 2017-04-17