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Historic Preservation - Technical Procedures

Spectitle:

Resetting Loose Sandstone Units

Procedure code:

0447004R

Source:

Internet - University Of Vermont

Division:

Masonry

Section:

Sandstone

Last Modified:

11/02/2012

Details:

Resetting Loose Sandstone Units



RE-SETTING LOOSE SANDSTONE UNITS


PART 1---GENERAL

1.01 SUMMARY

    A.  This procedure includes guidance on re-setting loose
         sandstone units.  GENERALLY, THIS PROCEDURE SHOULD BE
         PERFORMED BY AN EXPERIENCED CONTRACTOR.

    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 

1.03 QUALITY ASSURANCE

    A.  Standards:  ASTM C144, Aggregate for Masonry Mortar; ASTM
         C150, Portland Cement; ASTM C207, Hydrated Masons Lime;
         and manufacturer's printed recommendations for product
         use and installation.

    B.  Certifications:  Prior to delivery, submit certificates
         attesting to compliance with applicable specifications
         for grades, types and classes.

    C.  Joint Raking:  Prior to raking out all areas, cut back
         joints at location selected by Contracting Officer using
         the methods specified.  Raking will continue at no
         additional cost to the Government, until an acceptable
         sample is achieved.  This area will serve as standard for
         joint raking for the entire job.  It will be marked and
         left unpointed until all other pointing is complete.
         Point when directed by the Contracting Officer.

    D.  Sample Stone Pointing and Repair:  Repoint joints, re-
         attach stone fragments and repair stone using materials
         and methods specified at a location(s) selected by the
         Contracting Officer.  The samples accepted by the
         Contracting Officer will serve as a standard for the
         entire job.  They will be marked and left undisturbed.

    E.  To obtain sand/aggregate that matches historic, have a
         sample analyzed.  Color and texture should be closely
         matched to eliminate need for pigment additives which can
         fade and reduce strength of mortar.

1.04 PROJECT/SITE CONDITIONS

    A.  Environmental Requirements:  No stone pointing or repair
         shall be performed when the air temperature or stone
         surface temperature is 40 F and falling during and for 48
         hours subsequent to laying.


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Mortar for Bedding and Pointing:

         1.   Portland Cement:  Type 1, ASTM C150, gray and/or
              white mixed as necessary to match mortar color to
              original mortar.

         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.

         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

2.03 MIXES

    A.   Bedding Mortar Mix Proportions: Mix by Volume.

         1.   1 part Portland cement

         2.   2 parts lime putty

         3.   10 parts sand

         NOTE: DO NOT ADD PIGMENTS TO THE BEDDING MORTAR.

    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 ERECTION, INSTALLATION, APPLICATION

    A.   For Small Stones:

         1.   Carefully remove small shifted and/or loose
              sandstone units.  Clean of dirt, mortar, and loose
              debris.  Retain for re-use.  Re-build support
              masonry and lay new bedding material.

         2.   Remove loose debris from the stone cavity, and
              rinse with water to remove dust.  

         3.   Pre-wet adjacent surfaces with clean, potable
              water.

         4.   Re-set sandstone in an evenly filled bed of mortar,
              with full mortar coverage on horizontal and
              vertical joints. Maximum tolerances from plumb and
              level new work, not to exceed variation from plumb
              and level of adjacent existing work.  Match
              existing placement, pattern and location.  Note: If
              replacement units are required, they should match
              original sandstone in color, texture, and size, and
              be free from salts and other contaminants.

         5.   Construct uniform joints.  Shove vertical joints
              tight.  Adjust stone units to final position while
              mortar is soft and plastic.  Set stone with joints
              tooled back 1".  Point remaining depth as the rest
              of the stone is pointed.  See 04470-06-R for
              guidance on repointing sandstone.

         6.   Keep mortar and stone damp (80-90% RH) for 72 hours
              or until mortar is cured.

    B.   For Large Stones:

         1.   DO NOT REMOVE.

         2.   Tightly secure large stones using wooden wedges
              soaked in water.

         3.   Carefully clean joints of loose mortar and other
              debris and repoint in place.  See 04470-06-R for
              guidance on repointing sandstone.

3.02 ADJUSTING/CLEANING

    A.   At the time of repairing, patching, pointing and re-
         setting of the stone, immediately remove mortar, grout
         and adhesives from the face of the masonry.

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

                             END OF SECTION
 


resetting loose sandstone units, sandstone blocks