Marble, granite and natural stone are porous materials. This porosity is why it stains so easily. It is also why stains can be removed. All that’s needed to remove a stain is to reverse the staining process. In other words, the stone has literally absorbed the stain and we simply re-absorb it into a different material. This different material is what we call a poultice. A poultice can be made with powdered whiting and hydrogen peroxide or a chemical reducing agent-depending on the nature of the stain. Whiting is sold in most paint stores. The poultice should be made and applied as described for removal of each particular stain.
Most stains can be removed from natural stone with a process known as poulticing. Poulticing is similar to using a sponge to absorb liquid. A suitable powder material is mixed with a liquid cleaning agent and placed on the stain and allowed to dry. As it dries, it absorbs or draws the stain from the stone.
Although many powders such as diatomaceous earth, whiting, clay, and talc can be used and also paper towels and cotton balls, purchasing a good poultice powder from a stone and marble product supplier is best. A professional blend of the correct powders will insure that maximum drawing of the stain is achieved. The most important step in removing a stain is to first identify what caused it.
Each type of stain requires the use of a particular chemical or cleaning agent that will most effectively serve to dilute, break down and dissolve the stain. Following is a general guide that will suggest cleaning agents for the more common types of stains:
Please use extra caution when handling all chemicals listed above. Thoroughly read Safety Data Sheets for each chemical before use.
*Note that the Ammonium bi-fluoride used for rust stains may etch some stones that will require refinishing and polishing after. Always follow the manufacturer’s safety recommendations for the agent being used.
Applying the Poultice
Once the stain is identified, the following steps can be followed:
1. Wet the stained area with distilled water. Pre-wetting fills the pores of the stone with water isolating the stain and accelerating the removal by the chemical.
2. Prepare the poultice. If a poultice powder is to be used, pre mix the powder and the chemical of choice into a thick paste, the consistency of peanut butter. In other words, wet it enough so that it does not run.
3. Apply the poultice to the stain being careful not to spill any on the non stained areas. Apply approximately 1/4-inch thick overlapping the stain area by about one inch.
4. Cover the poultice with plastic (food wrap works great). Tape the plastic down to seal the edges. It also helps to poke several small holes in the plastic, so that the powder will dry out. Failure to do this may result in the poultice staying wet.
5. Allow the poultice to dry thoroughly. This is a very important step. The drying of the poultice is what pulls the stain from the stone into the poultice material. If the poultice is not allowed to dry, the stain may not be removed. Drying usually takes from 24 to 48 hours.
6. Remove the poultice from the stain. Rinse with distilled water and buff dry with a soft cloth. If the stain is not removed, apply the poultice again. It may take up to five applications for difficult stains.
Some chemicals may etch marble and limestone surfaces. If this occurs, then apply polishing powder and buff with a hand held buffer and a white or natural hair pad to restore the shine.