Repairing Sandstone By Through-Surface Repair

Procedure code:
Developed For Hspg (Nps - Sero)
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    A.   This procedure includes guidance on retaining delaminated
         sandstone with the use of adhesive grout and pins
         countersunk into the stone surface.  This procedure is
         known as Through Surface Repair.

    B.   Through Surface Repair is recommended for surfaces that
         are delaminated but cannot be composite patched, or if
         the void between layers exceeds 1/2".  Composite patching
         is the process of reconstructing missing stone surfaces
         by applying layers of cement/sand mixtures to the
         deteriorated surface.  For guidance on composite patching
         sandstone, see 04470-01-R.

    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).

    D.   For additional information on the characteristics, uses
         and problems associated with sandstone, see 04470-01-S.


    A.   American Society for Testing and Materials (ASTM), 100
         Barr Drive, West Conshohocken, PA 19428, (610) 832-9585
         or FAX (610) 832-9555.



    A.   E. I. Dupont de Nemours & Co., Inc.
         1007 Market Street
         Wilmington, DE  19898
         Teflon and Nylon Plus/dowels

    B.   Ernest F. Fullam, Inc.
         900 Albany-Shaker Road
         Latham, NY  12110
         60 mm. syringe

    C.   Sika Corporation
         201 Polito Ave.
         Lyndhurst, NJ  07071

    D.   Emerson & Cummings, Inc.
         59 Walpole St.
         Canton, MA  02021

    E.   Conservation Materials Ltd.
         P.O. Box 2884
         Sparks, NV  89432
         800/733-5283 or 702/331-0582
         Fluid Coke

    F.   Samuel Cabot, Inc.
         100 Hale Street
         Newburyport, MA  01950

    G.   Thoro System Products
         7800 NW 38th Street
         Miami, FL  33166


    A.   For Epoxy Resin Grout:

         1.   Epoxy resin such as "Sikadur Lo Mod" (Sika Chemical
              Corporation), or approved equal.

         2.   Microballoons (Emerson and Cummings, Inc.), or
              approved equal.

    B.   For Cementitious Grout:

         1.   Cement:  Portland cement ASTM C 150, Type II,

              NOTE:  DO NOT use gray cement; It is more difficult
              to color and work, shrinks more in curing, and may
              cause staining.

         2.   Microballoons (see Section 2.02 A.2. above)

         3.   Fluid coke (Conservation Materials, Ltd.), or
              approved equal

         4.   Cab-O-Sil (Cabot Corporation), or approved equal

         5.   Bonding agent such as ACRYL-60 (Thoro System
              Products), or approved equal

    C.   For Finish Coat:

         1.   Cement:  Portland cement ASTM C 150, Type II,

              NOTE:  DO NOT use gray cement; It is more difficult
              to color and work, shrinks more in curing, and may
              cause staining.

         2.   Lime: ASTM C 207, Type S, high plasticity:
              Increases cohesion during mixing, slows down the
              rate of cure, and moderates the qualities which
              could cause an excessively strong and moisture-
              resistant cement repair to fail and damage old

         3.   Sand:

              a.   Local natural sand, graded or masonry mortar
                   and conforming to ASTM C 144.

              b.   Sand color, size, and texture should match the
                   original as closely as possible to provide the
                   proper visual characteristics without other
                   additives.  A sample of the sand is necessary
                   for comparison to the original, and should be
                   approved by the consultant before beginning
                   repointing work.

              c.   The color of the sand shall be the primary
                   factor used to make mortars which match
                   existing adjacent fabrics.

         4.   Crushed Sandstone:

              a.   Best repairs contain actual sandstone; Use
                   stone removed from the area to be repaired, or
                   other old stone with the same qualities.

              b.   Grind it fine enough to pass through a 16-mesh
                   screen, and wash thoroughly.

         5.   Dry Pigments:

              a.   Use when available crushed stone is not
                   sufficient to give a color match.

              b.   Use stable fade-proof mineral oxide pigments
                   either natural- or synthetic-fade.

              NOTE:  DO NOT exceed recommended manufacturer's
              suggested maximum amounts; Too much pigment reduces
              strength and gives unstable color.  Maximum
              pigment/cement ratio to be 1/10 (verify with

         6.   Additives:

              a.   ACRYL-60 (Thoro System Products), or approved
                   equal:  Use only latex admixtures that are
                   labeled nonreemulsifiable like ACRYL-60; Do
                   not use bonding agents that may break down in
                   the presence of moisture.

                   GREENISH TINT.

    D.   Clean, potable water


    A.   Masonry drill with 1/4" drill bit

    B.   Pins (size to be 1/8" smaller than hole size)

    C.   60 mm (2 oz.) single-use syringe designed for use by
         veterinarians (Ernest F. Fullam, Inc.), or approved

    D.   Trowels

2.04 MIXES

    A.   Epoxy Resin Grout (simpler to use and stronger):

         1.   1 part Sikadur Lo Mod, or approved equal

         2.   2 parts Microballoons


    B.   Cementitious Grout (less hard and more flexible):

         1.   2 parts white Portland cement

         2.   2 parts Microballoons

         3.   2 parts fluid coke

         4.   1 part Cab-O-Sil, sizes 0-1

         5.   3 parts ACRYL-60, or equivalent

    C.   Finish Coat (for painting drill holes):

         1.   1 part white Portland cement

         2.   1 part Type S lime

         3.   2-3 parts sand

         4.   3-4 parts crushed sandstone

         5.   Dry pigments (maximum 10% by weight)

         6.   Mix with water and ACRYL-60, or equivalent in 5:1



    A.   Deterioration of sandstone due to moisture is evident as
         spalling, erosion, cracking, flaking and deteriorated
         mortar joints.

    B.   Before proceeding with any type of repair, examine the
         sandstone to determine the extent and the cause of the
         damage.  Compare undamaged stone with areas of suspected
         decay.  Use a magnifying glass if necessary.  Look
         closely at the following:

         1.   Color:  What color is the stone?  Is there
              variation in color within individual stones?  Is
              there variation between stones?

         2.   Pattern:  Are there swirls, bands, or veins of
              color within the individual stones?

         3.   Texture:  Is the stone surface rough or smooth?  Is
              it hard or crumbly?  Is the texture uniform or

         4.   Surface Tooling:  Is the face of the stone rough,
              smooth?  Are there any chiseled grooves?  Are there
              any decorative surface patterns?  Are any parts
              damaged or missing?

         5.   Sand Grains:  Is the grain size large or small?
              Are the grain shapes regular or irregular, uniform
              or varied?  Does the grain structure appear densely
              or loosely packed together?  Are there mica flakes
              present in the stone (these will often appear to
              glitter on the surface)?

         6.   Cementing Material:   What color is the material
              between the grains?  Do the grains project from the
              stone surface, giving the surface a rough texture?

         7.   Decay and Old Repairs:  Is there evidence of
              erosion, crumbling, spalling or other types of
              deterioration?  Is there evidence of previous
              patching or repairs?


    A.   Seal any cracks with a non-oily clay.

    B.   Drill staggered rows of holes no more than 1/4 inch in
         diameter through the face of the stone.

    C.   Using a 60mm syringe, inject adhesive grout (either epoxy
         resin-based or cementitious acrylic-based) into the
         drilled holes.

    D.   Insert pins into the grout-filled holes and countersink
         them; The pins should be 1/8 inch smaller than the hole.

    E.   Patch holes with finish coat of composite patching

                         END OF SECTION
Last Reviewed 2012-02-24