Resetting Loose Sandstone Units

PART 1–GENERAL

1.01 SUMMARY

1. This procedure includes guidance on re-setting loose sandstone units. GENERALLY, THIS PROCEDURE SHOULD BE PERFORMED BY AN EXPERIENCED CONTRACTOR.
2. 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

1. American Society for Testing and Materials (ASTM) www.astm.org

1.03 QUALITY ASSURANCE

1. 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.
2. Certifications: Prior to delivery, submit certificates attesting to compliance with applicable specifications for grades, types and classes.
3. 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.
4. 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.
5. To obtain sand/aggregate that matches historic, have an 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

1. 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

1. 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

1. Brushes: Natural fiber or nylon bristle only.
2. Mixing Vessels: Polyethylene plastic or as recommended by adhesive manufacturer.
3. Measuring Boxes
4. Joint tools
5. Chisel
6. Hammer
7. Hawk
8. Trowel
9. Putty knife

2.03 MIXES

1. 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.
      
2. 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.
3. 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

1. 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.
2. 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

1. 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.
2. Clean stone only with fiber bristle brushes and water. Use no acids, detergents or other cleaning agents.