Skip to main content

Historic Preservation - Technical Procedures

Spectitle:

Removing And Replacing Deteriorated Cast Stone Balusters

Procedure code:

0472001R

Source:

National Capitol Region Specifications

Division:

Masonry

Section:

Cast Stone

Last Modified:

11/01/2013

Details:

Removing And Replacing Deteriorated Cast Stone Balusters



REMOVING AND REPLACING DETERIORATED CAST STONE BALUSTERS


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on the removal of
         deteriorating exterior cast stone (concrete) balusters
         and their replacement.

    B.   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


    B.   American Concrete Institute (ACI), www.concrete.org

 

   C. Cast Stone Institute, www.caststone.org

 

   D. Architectural Precast Association, www.archprecast.org


        
1.03 SUBMITTALS

    A.   Product Data: Submit specifications and other data for
         cast stone, including certification that it complies with
         specified requirements. Include instructions for
         handling, storage, installation and protection.

    B.   Shop Drawings: Submit drawings showing sizes, dimensions,
         sections and profiles of cast stone units, arrangement
         and provisions for jointing, anchoring and fastening,
         supports and other necessary details for lifting devices
         and reception of other work. Indicate location of each
         unit on setting drawings with number designation
         corresponding to number marked on each unit.

1.04 QUALITY ASSURANCE

    A.   Regulatory Requirements: Provide cast stone which
         complies with requirements of "Specifications for Cast
         Stone" (ACI 704-44) of the American Concrete Institute;

        Or "Standard Specification for Architectural Cast Stone"
         (Section 04-72-00 (2011) of Cast Stone Institute;

        Or "Architectural Cast Stone" (Section 04720),
         Architectural Precast Association.
                  

    B.   Mock-Ups:

         1.   Prior to installation of stonework, provide one
              sample railing with all balusters to indicate
              proposed range of color, texture and workmanship to
              be expected in completed work. Build mock-up at
              site as directed, using stone, anchors and
              jointing, as specified in accordance with final
              shop drawings.

         2.   Obtain Contracting Officer's acceptance of visual
              qualities of balusters before start of stonework.
              Replace unsatisfactory mock-up work as directed,
              until acceptable to Contracting Officer. Retain
              sample panels during construction as a standard for
              judging completed stonework. Do not alter, move or
              destroy mock-up until work is completed.

1.05 DELIVERY, STORAGE AND HANDLING

    A.   Packing and Shipping:

         1.   Finished cast stone shall be carefully packed and
              loaded for shipment using all reasonable and
              customary precautions against damage in transit. No
              material which may cause staining or discoloration
              shall be used for blocking or packing.

         2.   Protect cast stone during storage and construction
              against moisture, soiling, staining and physical
              damage.

         3.   Handle stone to prevent chipping, breakage, soiling
              or other damage. Do not use pinch or wrecking bars
              without protecting edges of stone with wood or
              other rigid materials. Lift with wide-belt type
              slings wherever possible. Do not use wire rope or
              ropes containing tar or other substances which
              might cause staining.

    B.   Storage and Protection: Store stone on wood skids or
         pallets, covered with non-staining, waterproof membrane.
         Place and stack skids and stones to distribute weight
         evenly and to prevent breakage or cracking of stones.
         Protect stored stone from weather with waterproof, non-
         staining coverings or enclosures, but allow air to
         circulate around stones.

1.06 PROJECT/SITE CONDITIONS

    A.   Existing Conditions: Do not set cast stone in
         temperatures 40 F or below.

1.07 SEQUENCING AND SCHEDULING

    A.   Coordinating Work: Installer must review installation
         procedures and coordination with other work, with
         Contractor, and other contractors and subcontractors
         whose work will be affected by stonework.

PART 2---PRODUCTS

2.01 MANUFACTURERS

        See "References, 1.02" and consult industry groups (1.02 - B, C, and D)
         for membership directories.

2.02 MATERIALS

    A.   Cast Stone:

         1.   Cast stone shall be a building stone manufactured
              from Portland cement concrete, precast, and of the
              same composition throughout the piece.

         2.   Cement and aggregates shall be carefully chosen to
              produce a cast stone equal in color and texture to
              the appearance of the existing stone. Match only
              cleaned samples of the existing stone.

         3.   All added colors shall be mineral oxide pigments
              guaranteed by the manufacturer to be sun-fast and
              lime-proof.

         4.   Finish shall duplicate in all respects the finish
              of specific example(s) of the existing cast stone
              as designated by the Contracting Officer.

         5.   Aggregates shall be of known durability and shall
              be proportioned to produce maximum density.

         6.   Before delivery, cast stone shall be properly cured
              and shall have a minimum compressive strength of
              5,000 psi and a maximum average water absorption of
              7.5  percent.

         7.   All cast stone shall be sound and perfect. Make all
              edges sharp and true. Provide continuous slots,
              bevels, reglets, rebates and other features, as
              required.

    C.   Mortar and Grout:

         1.   Portland cement: ASTM C150, except complying with
              the non-staining requirements of ASTM C91 for not
              more than 0.03% water soluble alkali.

         2.   Hydrated Lime: ASTM C207, Type S.

         3.   Sand: ASTM C144.

         4.   Water: Clean and potable.

    D.   Stonework Accessories:

         1.   Anchors: Clean existing base anchors set in stone.

         2.   Setting Buttons: Lead or plastic buttons of the
              thickness required for the joint size indicated,
              and of the size required to maintain uniform joint
              width.

2.03 MIXES

    A.   Mortar: Non-staining, cement/lime mortar, complying with
         ASTM C270, Proportion Specification.  Mortar color should
         match adjacent historic mortar; match tooling and other
         details.


PART 3---EXECUTION

3.01 PREPARATION

    A.   Surface Preparation: Clean all adjoining stone surfaces
         before setting by thoroughly scrubbing with fiber
         brushes, followed by a thorough drenching with clear
         water. Use only mild cleaning compounds that contain no
         caustic or harsh fillers or abrasives. If not thoroughly
         wet at time of setting, drench or sponge stone.

3.03 ERECTION, INSTALLATION, APPLICATION

    A.   Measure the existing conditions prior to fabrication of
         the cast stone. Match the existing placement and
         dimensions.

    B.   Execute stonework by skilled mechanics, and employ
         skilled stone fitters at the site to do necessary field
         cutting as stone is set.

    C.   Set stone in accordance with drawings and final shop
         drawings for stonework. Provide anchors, supports,
         fasteners and other attachments shown or necessary to
         secure stonework in place. Shim and adjust accessories
         for proper setting of stone. Completely fill holes, slots
         and other sinkages for anchors, dowels, fasteners and
         supports with mortar during setting of stones.

    D.   Joints: Set units in full bed of mortar, unless otherwise
         indicated.

         1.   Wet stone thoroughly before setting.

         2.   Set stone before initial set of cement bed occurs.
              Do not set stone on dry bed. Tamp and beat stone
              for a complete contact between stone and setting
              bed. Set and level each unit immediately. Set stone
              in pattern shown with uniform joints.

         3.   Grout joints as soon as possible after initial set
              of setting bed. Force grout into joints, and tool.
              Wet joint surfaces, if dry, prior to grouting.

         4.   Cure grout by maintaining in a moist condition for
              7 days.

         5.   Remove grout spillage from face of stone as work
              progresses.

3.03 ADJUSTING/CLEANING

    A.   Clean stonework not less than six days after completion
         of work, using clean water and stiff-bristle brushes. Do
         not use wire brushes, acid-type cleaning agents or other
         cleaning compounds with caustic or harsh fillers.

                         END OF SECTION
 


cast stone, cast balusters