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Historic Preservation - Technical Procedures

Spectitle:

Repointing Sandstone

Procedure code:

0447006R

Source:

Internet - University Of Vermont

Division:

Masonry

Section:

Sandstone

Last Modified:

11/13/2012

Details:

Repointing Sandstone



REPOINTING SANDSTONE


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on raking out and
         repointing the deteriorated or inappropriately repointed
         horizontal and vertical joints on exterior sandstone.

    B.   Deteriorated mortar includes that which is excessively
         soft, crumbling, cracked, badly stained or missing.

    C.   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.

    D.   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

    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 recommendations for
         their application and use. Include test reports and
         certifications substantiating that products 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 exterior surfaces and elements not being repointed, such as: 
         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 a form of 6" long by 1/4 inch to 1/2 inch
         appropriately wide sample strips of mortar set in aluminum or plastic
         channels.  Width of channel forms should be similar to the existing mortar joints.

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 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 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.   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.   Existing Conditions: No stone work will be performed when
         the air temperature is 40 degrees F and falling or when stone
         surface temperature is 40 degrees F or below.

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.   Mortar for Pointing:

         1.   Portland Cement:  Type 1, ASTM C150, non-staining
              white as approved by RHPO to achieve proper color.

         2.   Hydrated Masons Lime:  ASTM C207, Type S.

         3.   Aggregate: Clean, sharp sand free of loam, silt,
              soluble salts and organic matter. Select
              aggregate and pigment to match the final mortar
              color to the color of the original mortar.  Sand
              should contain a full range of sizes from coarse to
              fine.

         
4.   Water:  Clean and free of deleterious amounts of
              oil, acid, alkalis and organic matter.

2.02 EQUIPMENT

    A.   Brushes:  Natural fiber or nylon bristle only.

    B.   Mixing Vessels:  Polyethylene plastic or as recommended
         by adhesive manufacturer.

    C.   Measuring Boxes

    D.   Joint tools

    E.   Chisel

    F.   Hammer

   
G.   Hawk

    H.   Trowel

    I.   Putty knife

    J.   Stiff fiber bristle brushes

    K.   Spray bottle

2.03 MIXES

    A.   General:  Replacement mortar MUST be weaker than the
         sandstone.  Mortars exposed to the weather should be
         formulated to resist erosion and freeze-thaw
         deterioration.  Mortars not exposed to severe weathering
         should be soft, flexible and durable.

         
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, unworkable 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.

         
5.   To insure proper color match between mixed mortars,
              the same person should mix all mortar for an entire
              job.

    B.   Pointing Mortar Mix Proportions (Type O): Typical for
         most wall surfaces, not directly exposed to the weather.

         Mix by volume the following:

         1.   1 part Portland cement

         2.   2 parts lime putty

         3.   12 parts sand

         
4.   Add pigments as required, but NEVER more than 10%
              of the total weight of portland cement.  Much
              smaller amounts are usually enough.  Always use the
              smallest amount necessary to produce the desired
              color and limit carbon black to 2%.  Pigments
              should be of mineral oxide composition.

   
C.   Pointing Mortar Mix Proportions (Type N): More common for
         surfaces directly exposed to the weather.

         Mix by volume the following:

         1.   1 part Portland cement

         2.   1 part lime putty

         
3.   10 parts sand

         4.   Add pigments as required, but NEVER more than 10%
              of the total weight of portland cement.  Much
              smaller amounts are usually enough.  Always use the
              smallest amount necessary to produce the desired
              color and limit carbon black to 2%.  Pigments
              should be of mineral oxide composition.


PART 3---EXECUTION

3.01 PREPARATION

    A.   Protection:

         1.   Protect persons, motor vehicles, landscaping, 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.

3.03 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.

             
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.

              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
              featheredge 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 only tools and equipment which are clean and free of
         hardened or partially hardened material. Use of metal
         scrapers or brushes will not be permitted.

   
C.   Clean sandstone only with fiber bristle brushes and
         water. Use no acids, detergents, or other cleaning agents

                             END OF SECTION
 


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