Skip to main content

Historic Preservation - Technical Procedures

Spectitle:

Re-Setting Loose Granite

Procedure code:

0446524R

Source:

National Capitol Region Specifications

Division:

Masonry

Section:

Granite

Last Modified:

06/14/2012

Details:

Re-Setting Loose Granite



RE-SETTING LOOSE GRANITE


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing displaced
         and cracked granite panels, repairing the substrate and
         re-installing the panels.

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

    B.   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.

    C.   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.

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 degrees F and falling during and for 48
         hours subsequent to laying.


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Stone: To match existing in grade, color and finish.

    B.   Lime:  Should conform to ASTM C207, Type S, high
         plasticity, Hydrated Lime for Masonry Purposes.  

         1.   Lime which meets this standard will "work" well,
              resists drying during curing, and is sufficiently
              strong for the purpose of repointing.  

         2.   Lime expands as it hydrates, making high lime
              mortars more resistant to crack formation.

    C.   Cement:  Should conform to ASTM C150, Type I, White.  It
         should not have more than 0.60% alkali nor more than
         0.15% water soluble alkali.  Use gray portland cement
         ONLY if a dark mortar is to be matched.

         1.   Cement meeting this standard should increase the
              workability of the mortar, accelerate the setting
              time and slightly increase the strength of the
              mortar.

         2.   The low alkali content will prevent efflorescence.

    D.   Sand:  Free of impurities and conforming to ASTM C144.  

         1.   Sand color, size, and texture should match the
              original as closely as possible.  Provide a sample
              of the sand for comparison to the original, and
              have it approved by the RHPO before beginning
              repointing work.

         2.   When possible, use bar sand or beach sand rather
              than crushed sand for the repointing mortar.

              NOTE:  BAR SAND OR BEACH SAND SHOULD BE WASHED TO
              REMOVE THE SALTS BEFORE USING.

              a.   Crushed sand has sharp edges, which makes it
                   more "sticky" and difficult to work into the
                   joints.  

              b.   Bar sand, on the other hand, has rounded edges
                   and flows easily during the mortar
                   application.  

              c.   The working characteristics of mortar made
                   with crushed sand may be improved by adding a
                   slight amount of portland cement.  The amount
                   of cement should be determined by
                   experimentation, but should not exceed 20% of
                   the total lime/cement binder.  20% OR LESS OF
                   CEMENT HAS MINIMAL EFFECT ON THE HARDNESS OF
                   THE MORTAR.  CEMENT CONTENT ABOVE 20% WILL
                   MAKE THE MORTAR TOO HARD.

    E.   Clean, potable water:  If the water must be transported
         or stored in a container, the container must not impart
         any chemicals to the water.

    F.   Stone dust finely ground from the same stone as that to
         be repointed.

    G.   Additives:  NO antifreeze compounds or other admixture
         shall be used.

         NOTE:  DO NOT USE ANTI-FREEZE COMPOUNDS.  THESE COMPOUNDS
         ARE DESIGNED FOR USE WITH CEMENT MORTARS, AND THEIR
         EFFECTIVENESS WITH HIGH LIME MORTARS IS QUESTIONABLE.
         FURTHERMORE, THE COMPOUNDS CONTAIN SALTS WHICH CAN LEAD
         TO SERIOUS PROBLEMS IN THE MASONRY AT A LATER TIME.  

         NOTE:  AIR ENTRAINING AGENTS ARE NOT RECOMMENDED.  THESE
         AGENTS ARE DESIGNED FOR USE WITH CEMENT RATHER THAN LIME,
         AND THEY RESULT IN DECREASED BONDING OF THE MORTAR AND
         THE MASONRY.  AIR ENTRAINING IS NOT NECESSARY WITH HIGH
         LIME MORTARS BECAUSE OF THE NATURAL ABILITY OF THESE
         MORTARS TO FLEX WITH TEMPERATURE CHANGES.

    G.   Epoxy grout

    H.   Reinforcement/Anchors:  Stainless steel type 302/304 3/8"
         in diameter threaded rods, length as required.

2.02 EQUIPMENT

    A.   Natural fiber or nylon bristle brushes

    B.   Wire bristle brush for cleaning anchors

    C.   Mixing Vessels

    D.   Joint tools

    E.   Chisel

    F.   Hammer

    G.   Hawk (plywood or steel mortar board)

    H.   Trowel

    I.   Hoe

    J.   Mesh screen

    K.   Putty knife

    L.   Wooden mortar boxes

2.03 MIXES

    A.   Some factors to consider when mixing lime mortar include
         durability, color and texture, and workability.

         1.   Durability:  Repointing mortar should be softer
              than the masonry units and the original mortar to
              reduce stresses at the edge of the masonry and, in
              the case of lime mortar, to reduce shrinkage which
              can cause cracks in the mortar.

              a.   If the new mortar is harder than the masonry
                   or the original mortar, it can cause serious
                   stresses within the wall during thermal
                   expansion and contraction, which can lead to
                   deterioration of the masonry units rather than
                   the mortar.  

              b.   If the mortar is softer, any deterioration
                   which occurs will take place in the mortar,
                   which is easier to replace than the units
                   themselves.  

         2.   The repointing mortar should allow the passage of
              water, both liquid and vapor.  If the mortar does
              not allow water to pass freely through it, the
              water can become trapped inside the wall, freeze
              and cause serious deterioration to the masonry.

         3.   Color and texture:  The repointing mortar should
              match the original mortar in color, texture and
              physical characteristics.

              a.   Obtaining an accurate color match is best
                   achieved by selecting an appropriate sand.

                   1)   Use sand which is similar to the original
                        in color and gradation.  Sand from more
                        than one source may be required.  

                   2)   For repointing of natural stones, use
                        finely ground stone "dust" in the mortar
                        to match the joints as closely as
                        possible to the stone.

              b.   If the original mortar was tinted, or if it is
                   impossible to obtain a color match through the
                   use of sand, it may be necessary to use a
                   special mortar pigment.  

                   CAUTION:  PIGMENTS MAY REACT WITH OTHER
                   INGREDIENTS IN THE MORTAR TO FORM
                   EFFLORESCENCE.  THEY MAY ALSO WEATHER AT A
                   DIFFERENT RATE THAN NATURAL COLORING AND CAUSE
                   A COLOR VARIATION IN THE MORTAR.  

                   NOTE:  IF PIGMENTS MUST BE USED, PURE MINERAL
                   OXIDES SHOULD BE USED BECAUSE THEY DO NOT FADE
                   OR LEACH OUT OF THE MORTAR.  AMOUNT OF PIGMENT
                   SHOULD NOT EXCEED 2% OF THE MORTAR MIX BY
                   WEIGHT.

              c.   Many mortars used before the twentieth century
                   have small lumps of incompletely burned or
                   ground lime, or other impurities.  To match
                   the original appearance of the masonry, these
                   impurities must be included in the new
                   repointing mortar.  Use identical materials,
                   such as ground oyster shells (obtained at feed
                   stores) or lumps of lime, to duplicate
                   original lumps.

         4.   Workability:  The workability or plasticity of the
              mortar is a direct result of the selection of
              materials.  

    B.   Mortar Mix:  

         1.  Have the existing mortar completely analyzed to
              determine its composition.  Use only repointing mortar
              that is softer and more permeable than the masonry units,  

              preferably matching the original mortar if it has performed 
              well and not caused damage to the masonry units.

         2.   Measure all ingredients by cubic volume using a
              pre-established uniform measure, such as a small
              bucket, rather than a less uniform measure such as
              a shovel.

         3.   For historic masonry set in lime mortar, use the
              following mortar mix:

              1 part portland cement
              3 parts lime
              8-12 parts sand (To match existing mortar as
              closely as possible.)

              NOTE:  The exact mix required will relate to the
              grain size and sharpness of the sand and will vary
              depending on the supply.  

              -OR-

              For historic masonry set in standard mortar, use
              the following mortar mix (ASTM C270 Type "0") as a
              starting point:

              1 part portland cement
              2 parts lime or lime putty
              6 to 9 parts sand and stone dust (To match existing
              mortar as closely as possible.)

              -OR-

              For Granite (ASTM C270 Type "S"):

              2 parts portland cement
              1 part lime
              7-9 parts aggregate
              Enough water to form a workable consistency

              NOTE:  FOR DETERIORATED GRANITE OR GRANITE WALLS
              INDICATING MOVEMENT, USE ASTM C270 TYPE "N" AS
              LISTED ABOVE FOR LIMESTONE.

         4.   Mix a final "job-size" batch once the correct sand
              color, cement content, etc. have been determined
              through small tests to ensure the on-site mixing
              conditions will result in the same final product.


PART 3---EXECUTION

3.01 ERECTION, INSTALLATION, APPLICATION

    A.   Carefully remove shifted and loose granite panels.  Clean
         of dirt, mortar, and loose debris.  Retain for re-use.
         Re-build support masonry and lay new bedding material.

    B.   Clean any exposed metal anchors of all corrosion by
         scraping and brushing with stiff wire brushes.  Replace
         any unsound anchors as necessary with new stainless steel
         anchors of same approximate size and shape.  Bed new
         anchors in epoxy grout.

    C.   Re-set granite, maximum tolerances from plumb and level
         new work, not to exceed variation from plumb and level of
         adjacent existing work.

    D.   Wet masonry and lay in full bed of mortar.  See 04100-03-
         S for mortar mixing procedures.  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.  For pointing
         procedures, see 04520-02-R.

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

3.02 ADJUSTING/CLEANING

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

    B.   Use only tools and equipment which are clean and free of
         hardened or partially hardened material.

    C.   After all work is complete, clean stone only with fiber
         bristle brushes and water.  Use no acids, detergents, or
         other cleaning agents.

                         END OF SECTION
 


displaced granited, cracked granite, resetting loose granite, reinstalling granite