Stain Removal Basics Natural stone, grout and some tiles stain easily because they are porous. Stains can normally be removed because of this porosity. Usually the stain can be removed from the stone using a poultice. A poultice is a material used to re-absorb the stain. A poultice can be made from many different materials. Diatomaceous Earth is my favorite powder form. It’s economical and can be purchased from the pool supply department of your favorite hardware store. Other materials that make fine poulticing powders are: clays (attapulgite, kaolin, fullers earth), talc, chalk (whiting), sepiolite (hydrous magnesium silicate) and methyl cellulose.  You can also use cotton balls, paper towels or gauze pads. Do not use whiting or iron type clays, such as Fullers Earth, with acidic chemicals. They will react with the material, canceling the effect of the poultice. First you need to identify the stain. First determine if it’s a stain or an acid etch. A stain is typically darker than the stone. An acid etch is typically lighter. On polished stone the acid etches will be dull and sometimes rough to the touch. An acid etch is more common on marble, travertine and limestone. Put your detective hat on if the stain ID is not obvious. If you still don’t know what the stain is, then you need to perform a patch test. Simply apply several different chemical poultices to various areas of the stain to determine which chemical will remove the stain. Most stains can be classified into one of the following categories:   Oil stains- cooking oil, bacon grease, tar, oil or other food stains, etc Poultice with ammonia and powder paste.   Organic stains- coffee, tea, plants, fruit, wine, tobacco, and some cosmetics, etc. Poultice with 20% to 40% Hydrogen Peroxide (available at beauty supply store) and powder paste.   Metal stains- Iron (rust) Poultice with Oxalic acid + powder + water. This poultice will etch polished marble, limestone and travertine and repolishing will be necessary. Copper, bronze – Ammonium Chloride and powder paste.   Biological stains- mildew, algae, lichens, etc- A. Thoroughly rinse the area to be treated with clean, clear water. B. Mix a solution of 3 parts household bleach with 1 part water and a dash of dishwashing detergent in a spray bottle. C. Thoroughly moisten the stained surface with this liquid by misting the surface using the spray bottle. D. Mist the surface continuously until the stain disappears. E. Rinse the surface with clean, clear water and allow to dry. F. Once the surface has dried completely, check for remaining residue and repeat the treatment if necessary. On tough mildew stains soak a paper towel in the bleach solution and poultice the stain overnight.     Ink stains- ink, pen, marker, etc- Poultice with mineral spirits or Methylene chloride and powder paste.   Paint- Poultice with commercial paint remover or mineral spirits and powder paste. Tough stains may require Methylene Chloride.   Please use extra caution when handling all chemicals listed above. Thoroughly read the Material Safety Data Sheets for each chemical before use.   Once the stain is identified clean the surface by first sweeping up any surface dirt and then clean the surface with a neutral stone clean to remove any surface soiling that didn’t sweep off. Wet the stained area with distilled water before applying the poultice. Wetting the stained area will help prevent the stain from being driven deeper into the stone. Prepare the poultice. If a powder is used, mix the chemical of choice with the powder until it is a paste the consistency of peanut butter, spread able but not runny. Apply the poultice to the stained area about ¼ inch thick and overlap the stain by about an inch. This will help prevent the stain from spreading beyond the poultice. Cover the poultice with plastic wrap. Tape the plastic down to seal the edges. Puncture a few holes in the plastic. Remove the plastic after 24 hours. Allow the poultice to dry thoroughly. This is an important step. The drying of the poultice is what pulls the stain from the stone into the absorbent poultice material. If the poultice does not dry thoroughly the stain may not be removed. Drying takes 48 to 72 hours. When dry, remove the poultice powder from the stain and rinse the area with distilled water and buff dry. After the surface has dried, if the stain is still visible you will need to apply the poultice again. It may take several applications to completely remove some stains.