Repairing Sandstone By Through-Surface Repair
- Procedure code:
- Developed For Hspg (Nps - Sero)
- Last Modified:
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:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- 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<</p>
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
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:
- Epoxy resin such as "Sikadur Lo Mod" (Sika Chemical Corporation), or approved equal.
- Microballoons (Emerson and Cummings, Inc.), or approved equal.
B. For Cementitious Grout:
- Cement: Portland cement ASTM C 150, Type II, white.
NOTE: DO NOT use gray cement; It is more difficult to color and work, shrinks more in curing, and may cause staining.
- Microballoons (see Section 2.02 A.2. above)
- Fluid coke (Conservation Materials, Ltd.), or approved equal
- Cab-O-Sil (Cabot Corporation), or approved equal
- Bonding agent such as ACRYL-60 (Thoro System Products), or approved equal
C. For Finish Coat:
- Cement: Portland cement ASTM C 150, Type II, white. NOTE: DO NOT use gray cement; It is more difficult to color and work, shrinks more in curing, and may cause staining.
- 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 stone.
- Local natural sand, graded or masonry mortar and conforming to ASTM C 144.
- 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 re-pointing work.
- The color of the sand shall be the primary factor used to make mortars which match existing adjacent fabrics.
- Crushed Sandstone:
- Best repairs contain actual sandstone; Use stone removed from the area to be repaired, or other old stone with the same qualities.
- Grind it fine enough to pass through a 16-mesh screen, and wash thoroughly.
- Dry Pigments:
- Use when available crushed stone is not sufficient to give a color match.
- 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 manufacturer).
- 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.
CAUTION: ADMIXTURE ABOVE RECOMMENDED AMOUNTS GIVES A GLOSSY, ARTIFICIAL LOOK, AND CAUSES A 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 equal.
A. Epoxy Resin Grout (simpler to use and stronger):
- 1 part Sikadur Lo Mod, or approved equal
- 2 parts Microballoons
B. Cementitious Grout (less hard and more flexible):
- 2 parts white Portland cement
- 2 parts Microballoons
- 2 parts fluid coke
- 1 part Cab-O-Sil, sizes 0-1
- 3 parts ACRYL-60, or equivalent
C. Finish Coat (for painting drill holes):
- 1 part white Portland cement
- 1 part Type S lime
- 2-3 parts sand
- 3-4 parts crushed sandstone
- Dry pigments (maximum 10% by weight)
- Mix with water and ACRYL-60, or equivalent in 5:1 ratio
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:
- Color: What color is the stone? Is there variation in color within individual stones? Is there variation between stones?
- Pattern: Are there swirls, bands, or veins of color within the individual stones?
- Texture: Is the stone surface rough or smooth? Is it hard or crumbly? Is the texture uniform or varied?
- 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?
- 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)?
- Cementing Material: What color is the material between the grains? Do the grains project from the stone surface, giving the surface a rough texture?
- 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 material.