All natural stones, irrespective of their hardness, are absorbent. These are due to some stone properties that relate to porosity, permeability and absorption. Thus making all natural stones vulnerable to staining. Spills, if not immediately attended to, tend to cause a stain on the surface of the stone, which becomes hard to remove.
Staining may occur due to various reasons and it is very problematic because
- Some stones have moisture sensitive minerals, and substances that cause the stone to stain
- Old stains, may not be fully removed leaving a light shadow
- Stubborn stains may become permanent, and cannot be removed at all
- Minerals in the stone have a definite chemical composition, causing chemical reactions between them and the staining substances, causing an irreversible change.
How do we deal with stained surfaces then? Is there no solution at all? We can remove most stains, by carefully identifying the type of stain. Different types of stains react differently to Chemical agents. Using the wrong chemical on the wrong type of stain might cause adverse reactions, thereby making it a permanent problem.
Stains are classified into five broad categories
- Organic: Food, fruits, coffee, tea, beverages, cosmetics and tobacco
- Oil Based: Greasy food, Cooking oils, grease, tar, skin and hair oils.
- Inks/Dyes: Felt Pens, markers, natural and synthetic dyes
- Biological: Vegetation, mold, mildew, algae, fungus, etc.
- Metallic: Rust, Copper, Bronze, etc.
Sometimes the cause of the stain is not known. Most stains fall into one of the above five categories. Colour may also give an indication of what kind of stain it is.
| Black | Oil, Grease, Tar, Asphalt, Ink, Shoe polish, Mold, Moss, Fungus, Mildew, Animal faeces, Vegetation, Dirt |
| Brown Shades | Coffee, Tea, Food, Chocolate, Grease, Oil, Algae, Moss, Vegetation, Dirt, Wood (tannin), Tobacco, Urine, Animal faeces, Rust, Copper, Bronze, Dyes, Plant fertilizer |
| Red Shades | Food, Fruit drinks, Blood, Ink, Dyes, Rust, Plant fertilizer, Dirt |
| Orange | Foods, fruit drinks, rust, dyes |
| Green | Algae, mildew, foods, ink, dyes, copper, bronze |
| Yellow | Eggs, mustard, oil, grease, urine, rust |
| Amber | Varnish, polyurethane |
| Blue | Plant fertilizer, ink, dyes |
| Greenish-Blue | Copper, bronze |
| Gray | Aluminum, efflorescence, paper |
| White | Aluminum, efflorescence, plant fertilizer, paint,/td> |
| Clear | Eggs, shellac, lacquer, varnish, urethane, polyurethane |
| Other | Paint, ink, crayon (wax), dyes, cement coloring stains, pigmented sealers, colored past waxes, colored grouts |
Stain Removal
Stains on porous stones have to be pulled out of the pores. This is done by applying absorbent material on the stained area. This process is referred to as poultice. There are several premixed wet poultice products available in the market. There are also powder based products which are activated by mixing water. It is safer to use a premixed product than to formulate your own poultice.
Here is a video that shows how exactly a wet poultice should be used.
It is a practice to keep the poultice wrapped down on the stone using plastic. This prevents the poultice from drying out soon and helps retain moisture, which is required for the chemicals to work. There might be a dark patch on the area of poultice application, even after removal. This takes a couple of days to dry. Some stains would require more than one application of poultice to make them stain free. The general rule is that even after two applications of poultice, if the stain persists, it is probably a permanent stain.
Here is a small guide on how to remove different types of stains. IF you are doubtful at any stage, consult a stone care professional, as wrong treatment may lead to permanent damage.
| Type of Stain | Directions |
|---|---|
| Organic Stains | Mix hydrogen peroxide with a few drops of ammonia. Pour on the stain and leave until the fizzing stops. Use brush to work in. Rinse with water. If it lightens repeat. If this does not work apply the commercial poultice according to the instruction. More than one application may be necessary. |
| Oil-Based Stains | Apply poultice. Oil stains usually require a few application to to be removed. |
| Ink/Dye Stains | For light colored marble and limestone… add about 1 inch of “DI DI Seven” with enough water to mix with poultice. More than one application may be needed. I have had great success with this method. For dark marbles…Wipe with Acetone. |
| Biological Stains | Spray with a solution of 3 parts bleach, 1 part water and a few drops of dish detergent. Scrub with a brush unit gone. Rinse thoroughly with clean water. |
| Metallic Stains | DO NOT USE BLEACH! Use suitable metal stain remover product. |
Note: Mark Corporation is a manufacturer of superabrasive diamond tools for processing granite, marble and other natural stones. We are not manufacturers/processors of cleaning agents/chemicals forgranite, marble or any other stone. For queries regarding stone care, use the contact form on the site. Our assistance team will get in touch with you to clarify any of your doubts.
About The Blog Author
Mr. R. Arvind, is the director of Mark Corporation, Chennai. Read his articles about stone processing, abrasives, and business in general. 