Surface stains can often be removed by cleaning with an appropriate commercial cleaning product or household chemical. Identifying the type of stain is the key to removing it. Look for color, shape, and environmental factors that could be causing the staining.
Types of Stains And Removal Procedures
- Oil-based stains (grease, tar, cooking oil, cosmetics). An oil-based stain will darken the stone and normally must be chemically dissolved so the source of the stain can be flushed or rinsed away. Remove excess staining agent by wiping or chipping (if tar) first. Clean gently with a soft liquid cleanser, household detergent, ammonia, mineral spirits, or acetone. Do not pour the cleaner directly on the staining agent – this can result in thinning the contaminant and furthering its spread. Partially saturate a paper or cloth towel with the cleaner and attempt to draw the stain into the towel. Commercially available specialty cleaners, such as alkaline degreasers and/or poultices may also be used.
- Organic stains (coffee, tea, fruit, tobacco, paper, food, urine, leaves, bark, bird droppings) may cause a pinkish-brown stain and may disappear after the source of the stain has been removed. Outdoors, with the sources removed, normal sun and rain action will generally bleach out the stains. Indoors, clean with 12% hydrogen peroxide and a few drops of ammonia. Commercially marketed cleaners and poultices are also available.
- Inorganic metal stains (iron, rust, copper, bronze). Iron or rust stains are orange to brown in color and leave the shape of the staining object, such as nails, bolts, screws, cans, flowerpots, or metal furniture. Copper and bronze stains appear as green or muddy brown and result from the action of moisture on nearby or embedded bronze, copper, or brass items. Metal stains must be removed with a poultice (see Section 9.0 of this chapter on Poultices). Deep-seated, rusty stains are extremely difficult to remove, and the stone may be permanently stained.
- Biological stains (algae, mildew, lichens, moss, fungi). Clean with dilute (ó cup in a gallon of water) ammonia, bleach, or hydrogen peroxide. WARNING: DO NOT MIX BLEACH AND AMMONIA! THIS COMBINATION CREATES A TOXIC GAS!
- Ink Stains (magic marker, pen, ink). Clean light-colored stones with bleach or hydrogen peroxide. Use lacquer thinner or acetone for dark-colored stones. Do not pour the cleaner directly on the staining agent – this can result in thinning the contaminant and furthering its spread. Partially saturate a paper or cloth towel with the cleaner and attempt to draw the stain into the towel.
- Paint Stains. Small amounts can be removed with lacquer thinner or scraped off carefully with a razor blade. Heavy paint coverage should be removed with a commercial liquid paint stripper. DO NOT USE ACIDS OR FLAME TOOLS TO STRIP PAINT FROM STONE.
- Water spots and rings (surface accumulation of hard water). Buff with dry 0000 steel wool.
- Fire and Smoke Damage. Older stones and smoke- or fire-stained fireplaces may require a thorough cleaning to restore their original appearance. Commercially available smoke removal products may save time and effort.
- Etch Marks. Caused by acids left on the surface of the stone, some will etch the finish but not leave a stain; others will both etch and stain. Once the stain has been removed, wet the surface with clear water and sprinkle with marble polishing powder. Rub the powder into the stone with a damp cloth or by using a buffing pad with a low speed power drill or polisher. Continue buffing until the etch mark disappears and the marble surface shines. Honing may be required for deep etching. This process may require the services of a Professional Refinisher.
- Efflorescence. A white powder that may appear on the surface of the stone, it is caused by water carrying mineral salts from below the surface of the stone to the surface and evaporating. When the water evaporates, it leaves the powdery salt residue. If the installation is new, dust mop or vacuum the powder. Repeat as necessary as the stone dries out. Do not use water to remove the powder. If the problem persists, contact the Contractor to identify and remove the cause of the moisture.Source: Marble Institute of America – Cleaning and Maintenance