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Historic Preservation - Technical Procedures

Spectitle:

Removing And Replacing Deteriorated Stone Masonry

Procedure code:

0440004R

Source:

Developed For Hspg (Nps - Sero)

Division:

Masonry

Section:

Stonework

Last Modified:

02/24/2012

Details:

Removing And Replacing Deteriorated Stone Masonry



REMOVING AND REPLACING DETERIORATED STONE MASONRY


THIS PROCEDURE SHOULD BE PERFORMED UNDER THE DIRECTION OF AN
HISTORICAL ARCHITECT OR ENGINEER TO DETERMINE THE MOST EFFICIENT
AND LEAST DESTRUCTIVE MANNER FOR EXECUTING THE WORK.  APPROVAL
FROM
THE REGIONAL HISTORIC PRESERVATION OFFICER IS REQUIRED.


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing and
         replacing deteriorated stone masonry.  It should be used
         in conjunction with procedure 04520-02-R "Repointing
         Masonry Using Lime Mortar" and 04100-03-S "Preparing Lime
         Mortars for Repointing Masonry".

    B.   Damage to stone in the form of cracking, splitting and
         spalling often occurs in areas sheltered from direct
         rain-washing.

    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 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), 100
         Barr Drive, West Conshohocken, PA 19428, (610) 832-9585
         or FAX (610) 832-9555.

1.03 PROJECT/SITE CONDITIONS

    A.   Environmental Requirements:

         1.   Weather:  Do not proceed with patching or
              replacement under adverse weather conditions, or
              when temperatures are below or above manufacturer's
              recommended limitations for installation;  Proceed
              with the work only when forecasted weather
              conditions are favorable for proper cure.

         2.   Wet Weather:  Do not apply or mix mortar on outside
              surfaces with standing water or outside during
              rain.

         3.   Cold Weather, winter construction is not allowed
              without consent of Regional Architect;  Winter
              construction (midwest region) is defined as any
              time between December 1 and March 1 and/or when
              surface temperature of masonry is below 40oF. or
              air temperature is predicted to be below 40oF.
              within 48 hours; Heat mortar materials to above
              40oF. if necessary.

         4.   Hot Weather:  The surface temperature of the work,
              not the ambient temperature, should not be higher
              than 100oF.; Mortar mixing should be done only in
              the shade; Cover mortar in hot weather to reduce
              evaporation; Pointing work should be done in the
              shade;  Work around the building during the day so
              that the fresh work will be shielded from direct
              sunlight to reduce evaporation rate.

         5.   All work must be suspended during frosty weather
              unless a heated enclosure is provided.  Work should
              not be done in full sun at temperatures above 27oC.
              unless shading of the walls is provided and the
              masonry wall temperature is kept below this point;
              Burlap sacking and water misting may be necessary
              to control evaporation; High temperatures can cause
              flash setting of cements and rapid evaporation of
              water in the mix, leading to lack of development of
              final strength by the cement.

         6.   Special Precautions and Notes:  Do not allow
              masonry to freeze until mortar is thoroughly dry
              and hardening almost complete (approx. three days
              time); The setting of lime mortar is very much
              slower than that of cement mortar because the
              curing requires the absorption of carbon dioxide to
              form hard lime carbonates; It is a very lengthy
              process, so do not expect it to become hard
              immediately, especially at the core of large masses
              of masonry.


PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.   Repointing Tools:  Available from good hardware stores,
         building material suppliers or mail-order catalogues.

         1.   The Stanley Gold-blatt Tool Co.
              511 Osage Ave.
              Kansas City, KS  66105-2198
              913/621-3010

         2.   Marshalltown Trowel Co.
              P.O. Box 738
              Marshalltown, IA  50158
              515/753-5999

         3.   Masonry Specialty Co.
              4430 Gibsonia Rd.
              Gibsonia, PA  15044
              412/443-7080

2.02 MATERIALS

    A.   Salvaged Stone:  Approved, sound, crack free, clean stone
         without face chips larger than 1/2 inch, salvaged from
         removed face stone work.

    B.   Replacement Stone:  Upon approval of Regional Historic
         Preservation Officer, provide natural building stone of
         type (classification) and with color, and surface texture
         to match existing stone on building.  Match existing
         stones in size and shape.

    C.   Lime

    D.   Naturally colored binder such as (PFA) low sulphate
         pozzolanic fly ash

    E.   HTI Powder (white refractory brick powder - "High
         Temporary Insulation") - may be used as a pozzolanic
         additive to make a weak hydraulic mortar.

    F.   Mortar and Grout Materials:  

         1.   Portland Cement:  ASTM C150, Type I.

              a.   For stonework and other masonry indicated,
                   provide non-staining white cement complying
                   with staining requirement 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.

              a.   Colored Mortar Aggregate:  Natural or
                   manufactured sand selected to produce mortar
                   color indicated.

         4.   Colored Mortar Pigment:  Natural and synthetic iron
              oxides and chromium oxides, compounded for use in
              mortar mixes.  Use only pigments with record of
              satisfactory performance in masonry mortars.

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

         6.   Aggregate for Grout:  ASTM C404.

    G.   Manufactured and raw materials accessory to the primary
         products.

         1.   Supports, fasteners, installation accessories, and
              anchors:  Stainless steel only for use with
              granite.  Brass, bronze, or stainless steel for use
              with limestone and other masonry.

         2.   Flashings or barriers:  Sheet copper or as
              detailed.

2.03 EQUIPMENT

    A.   Trowels:  range in length from 10-12 inches

    B.   Chisels:  Joint chisels or a standard mason's chisel with
         a 1-1/2 in. blade and a long narrow handle

    C.   Hammers:

         1.   5# stone dressing hammer

         2.   2# striking hammer

         3.   "No-Bounce" hammer

         4.   Full size and one half size brick hammers

    D.   Joint Tools:  (see 2.01 MANUFACTURERS above)

         1.   3/8"-1/4" raised beaded tool

         2.   3/8"-1/4" beaded striking tool

         3.   1/2" raised beaded tool with offset handle

         4.   1/2" flat joint iron

         5.   Pointing tool should be about 1/16" narrower than
              the joint being filled to achieve good compaction

    E.   Hawks:  Plywood or steel hawk (mortar board)

    F.   Brushes:

         1.   Natural bristle brushes

         2.   Stiff bristle brushes (no wire)

    G.   Spray bottle

2.02 MIXES

    A.   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 mechanical batch
         mixer.

    B.   Consistently and accurately measure materials for each
         batch.

    C.   Mix for at least five minutes in a mechanical batch mixer
         or mortar box.

    D.   Mix trowel workable consistency for unit masonry setting
         and resetting.

         1.   Mixer 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.

    E.   Mix firm dry consistency for repointing.

    F.   Discard mortar not used within two hours after mixing; do
         not retemper at mixer.

    G.   Dispose of waste mortar and cleaning water in approved
         manner; do not contaminate the site, adjoining property,
         or waste to sewers.

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

         1.   Color Pigmented Mortar:  Where colored mortar
              pigments are indicated, do not exceed pigment-to-cement ratio of 1-to-10, by weight.

         2.   Match original color and texture for each kind of
              mortar and masonry work.

         3.   Match to inner mortar color which has been
              protected from weathering and soiling, not face
              color.

         4.   Conform to the dry mix color matching, "A Fast
              Method of Matching Mortar Colors Using Heat,"  APT
              Bulletin, Vol. X, No., 2, 1978, pp. 79-85, copy
              provided by RHPO; or other method approved.

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

    J.   Mortar Proportions:

         NOTE:  VERIFY PROPORTIONS WITH MORTAR ANALYSIS TO MATCH
         OR RESEMBLE HISTORIC MORTAR.

         1.   Pointing Mortar for Stone:  One part white portland
              cement, 1 part lime, 6 parts colored mortar
              aggregate.

         2.   Rebuilding Mortar:  Comply with ASTM C270,
              proportion Specification, Type N, unless otherwise
              indicated with cementitious material content
              limited to portland cement-lime.

         3.   Grout:  ASTM C476.


PART 3---EXECUTION

3.01 PREPARATION

    A.   Surface Preparation:  Where fresh masonry joins existing
         work, clean the exposed surface of the set masonry by
         removing loose stone and mortar and wet lightly to obtain
         the best possible bond with the new work.

3.02 ERECTION/INSTALLATION/APPLICATION

    A.   Carefully remove by hand, as indicated, any stone which
         has deteriorated, shifted, or is damaged beyond repair.

         1.   Carefully cut out perimeter joints of stone by hand
              using a hammer and chisel.

         2.   Break down the rest of the damaged stone with
              vertical saw cuts and break it up with a hammer and
              chisel.

    B.   Carefully clean out the cavity to receive the stone.
         Remove mortar, loose particles and other debris from in
         preparation for resetting.

    C.   Thoroughly wet the cavity with water; Dampen the new or
         salvaged stone with water.

    D.   Spread a 1/2 inch thick mortar bed into the open cavity;
         the new mortar should consist of coarse sand and grit to
         match the original mortar.  Butter vertical joints for
         full width before setting and set unit(s) in full bed of
         mortar, unless otherwise indicated.

    E.   Repair and/or replace removed stone with salvaged stone,
         where possible, or with new stone to match existing,
         including size.  Set the stone in the cavity.

    F.   Fill the joints with a grout of lime and low sulphate
         pozzolanic fly ash (PFA) or lime and HTI powder.

    G.   Tool joints after setting to match joints of surrounding
         stone.

    H.   Repoint new mortar joint to comply with requirements for
         repointing existing masonry, except rake out joints
         before mortar sets.

3.03 ADJUSTING/CLEANING

    A.   Wipe all excess mortar as the work progresses.  Dry brush
         at the end of each day's work.  After mortar is
         thoroughly set and cured, clean new masonry surfaces,
         walls, sills, overhangs, etc., of all loose mortar, and
         dirt and point up all nail holes, cracks, etc., after
         which wash down all masonry walls, leaving them clean and
         neat.

                         END OF SECTION