Removing Mortar Deposits And Stains From Marble

CSI Division
Division 4- Masonry
Section
Marble
Last Modified

Technical Procedures Disclaimer

Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.

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We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.

THE CLEANING OR REMOVAL OF STAINS FROM STONE MAY INVOLVE THE USE OF LIQUIDS, DETERGENTS OR SOLVENTS WHICH MAY RUN OFF ON ADJACENT MATERIAL, DISCOLOR THE STONE OR DRIVE THE STAINS DEEPER INTO POROUS STONES. USE THE PRODUCTS AND TECHNIQUES DESCRIBED HERE ONLY FOR THE COMBINATIONS OF DIRT/STAIN AND STONE SPECIFIED.

PART 1–GENERAL

1.01 SUMMARY

  1. This procedure includes guidance on removing mortar deposits or other concrete-based residues from marble. Mortar deposits may be spattered onto adjacent surfaces during repointing or other repair work. If left on the surface, these deposits and residual film can be difficult to remove.
  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).
  3. For guidance on the general cleaning of marble, see 04455-06-R.
  4. For general information on the characteristics, uses and problems associated with marble, see 04455-01-S.

PART 2–PRODUCTS

2.01 MANUFACTURERS

  1. ProSoCo, Inc. www.prosoco.com

2.02 MATERIALS

NOTE: Chemical products are sometimes sold under a common name. This usually means that the substance is not as pure as the same chemical sold under its chemical name. The grade of purity of common name substances, however, is usually adequate for stain removal work, and these products should be purchased when available, as they tend to be less expensive. Common names are indicated below by an asterisk (*).

  1. Hydrochloric Acid (30-35%):
    1. A strong corrosive irritating acid.
    2. Other chemical or common names include Chlorhydric acid; Hydrogen chloride; Muriatic acid* (generally available in 18 degree and 20 degree Baume solutions); Marine acid*; Spirit of salt*; Spirit of sea salt*.
    3. Potential Hazards: TOXIC, CORROSIVE TO FLESH; CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS, FLAMMABLE. CAN CAUSE ETCHING OF POLISHED MARBLE.
    4. Available from chemical supply house, drugstore or pharmaceutical supply distributor, or hardware store.
  2. Clean, potable water
  3. Liquid Marble Cleaner: A water-soluble non-acidic chemical cleaner manufactured specifically for restorative type cleaning of polished and honed marble surfaces. Cleaner shall contain no abrasives, grease, lye, or other caustic or corrosive ingredients, such as “Sure Klean 942 Limestone and Marble Cleaner” (ProSoCo, Inc.) or approved equal. May damage highly polished surfaces, do test sample area.
  4. Drying Materials: Clean natural fiber rags

2.03 EQUIPMENT

  1. Garden hose and nozzle
  2. Stiff bristle brushes (non-metallic)
  3. Wood or plastic scraper

PART 3–EXECUTION

3.01 EXAMINATION

  1. Examine the marble surface CAREFULLY to determine the cause of staining before proceeding with any cleaning operation.

3.02 PREPARATION

  1. Protection:
    1. Provide adequate wash solutions (i.e. water, soap and towels) before starting the job.
    2. Whenever acid is used, the surface should be thoroughly rinsed with water as soon as its action has been adequate. Otherwise it will continue etching the masonry even though the stain is gone.

3.03 ERECTION, INSTALLATION, APPLICATION

NOTE: TEST CLEAN A SMALL AREA BEFORE ATTEMPTING TO CLEAN

LARGE AREAS. LET TEST AREA REST FOR SEVERAL WEEKS AND EXAMINE TO DETERMINE IF ANY ADVERSE IMPACTS. SEEK ADVICE FROM THE RHPO.

  1. If possible, remove large pieces of mortar deposits using a wood or plastic scraper.
  2. For light staining: Clean the surface with a commercial stone cleaner and water. Follow manufacturer’s instructions.
  3. For more difficult staining:
    1. Wash down the affected area with a diluted solution of hydrochloric acid. CAUTION: HYDROCHLORIC ACID CAN SEVERELY ETCH POLISHED MARBLE SURFACES. USE EXTREME CAUTION AND FOLLOW MIXING INSTRUCTIONS CAREFULLY.
      1. For textured stone, mix 1 part hydrochloric acid with 20 parts water.
      2. For polished stone, mix 1 part hydrochloric acid with 40 parts water.
    2. Agitate the treated surface with a stiff fiber bristle brush.
    3. Thoroughly rinse the surface with clean, clear water and allow to dry.
    4. If necessary, re-hone or re-polish the surface. See 04455-02-P for guidance on re-polishing.

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Last updated: Aug 13, 2017
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