Removing Yellow Discoloration from Marble

PREFACE

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 specification provides guidance on removing yellow discoloration from marble surfaces. Yellowing may result from any of the following:

   1. Discoloration of waxes or other coatings applied to the marble surface.

   2. Exposure to ultraviolet light over a long period of time.

   3. Oxidation of iron oxides in the marble.

   4. Mastics used to set the marble.

2. Read “General Project Guidelines” along with this specification. 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). The 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)

3. See also: “Marble: Characteristics, Uses and Problems”.

PART 2–PRODUCTS

2.01 MATERIALS

1. Clean, cold water.

2. Chelating agent such as ethylenediaminetetraacetic acid (EDTA), which is used to remove metallic stains from masonry.

   1. The chelating agent serves to keep any iron suspended in the water so it does not settle on the stone.

   2. Chelating agents are molecules that pull metal ions together. The metal ions in the stain attach themselves to the chelating agent to form either a soluble or insoluble metal complex that can then be removed.

   3. Available from chemical supply house.

   4. Available as an acid or in the form of its more soluble sodium salts.

   5. Also used as a preservative but its most important use is for removing unwanted metal ions from water, as in the manufacturing of agricultural chemical sprays.

   6. For use on acid-sensitive masonry, which includes:

      1. Limestone

      2. Marble

      3. Calcareous sandstone

      4. Glazed brick

      5. Sand-lime brick

      6. Architectural terra cotta

      7. Polished granite.

2.02 EQUIPMENT

This procedure requires a stiff bristle brush (non-metallic).

PART 3–EXECUTION

3.01 EXAMINATION

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

3.02 ERECTION, INSTALLATION, APPLICATION

1. If the yellowing is caused by oxidation of iron inherent in the marble or caused by age, removal of the staining will be impossible. Natural characteristics and aging of the stone cannot be reversed.

2. If the yellowing is caused by the deterioration of waxes or other coatings that have been applied to the marble surface, strip the coatings from the marble (see “Removing Built-Up Coatings from Interior Marble” for guidance) and re-polish or re-hone as desired (see “Re-polishing Marble”).

3. If the yellowing results from iron deposited on the surface from cleaning water that contains high levels of iron, try one of the following:

   1. Wash the stone with water and a chelating agent such as EDTA (Ethylene diamine Tetra-acetic Acid), or approved equal. Scrub the surface using a stiff bristle brush (non-metallic bristle).

      1. Allow the cleaner to stand on the surface for approximately 1 hour or as recommended by manufacturer.

      2. Thoroughly rinse the surface with clean, clear water and allow to dry.

-OR-

Wash the stone using a commercial rust remover. See “Poulticing Rust Stains from Limestone and Marble” for guidance.