Natural stone surfaces can be found commonly in many places —in office-building entryways, on credenzas and countertops, around pools. And building service contractors can keep these surfaces looking good with a few basic tools and procedures.

First, identify the type of surface you’re working with. Natural stone can be classified into two general categories:

Siliceous stone mainly is composed of silica or quartz-like particles. It tends to be durable and relatively easy to clean with mild acid solutions. Granite, slate, sandstone, quartzite, brownstone and bluestone are types of siliceous stone.

Calcareous stone primarily is composed of calcium carbonate. It is sensitive to acidic products, and frequently requires different cleaning procedures from siliceous stone. Types of calcareous stone include marble, travertine, limestone and onyx.

Stone colors and appearances
Granites and marbles are quarried throughout the world in a variety of colors, due to the differences in mineral composition. Generally, marble will show "veins" of mineral particles, whereas the minerals in granite will appear as small flecks distributed throughout the stone.

Sandstones vary widely in color due to minerals and clays. Sandstone is light gray to yellow or red. A dark reddish-brown sandstone, also called brownstone, commonly is used in the northeastern United States and eastern Canada. Bluestone is a dense, hard, fine-grain sandstone of greenish- or bluish-gray color that is quarried in the eastern United States.

Limestone widely is used for construction, with colors typically light gray, tan or buff. Many limestones have visible fossils in the stone surface.

Slate most commonly is used as a flooring or roofing material, and is often distinguished by its cleft texture. It comes in a variety of hues.

Stone surfaces also are distinguished by their finishes. A polished finish has a glossy surface that reflects light and emphasizes the color and markings of the material. This finish commonly is used on walls, furniture and floors.

A honed finish is a satin-smooth surface that is used where heavy traffic will quickly wear off a polished surface.

A flamed finish is a rough surface used frequently on granite floors.

Care and precautions
To avoid damage to stone surfaces, contractors can educate their customers about a few preventative tips:

  • Use coasters under all glasses, and avoid spilling. Alcohol, citrus juices and other acidic foods might etch or dull the surface.
  • Do not place hot items directly on stone.
  • Use matting or other barriers under planters, desks or filing cabinets or other objects that might scratch stone floors.
  • Use mats or area rugs near entrances to minimize sand, dirt and grit that will scratch a stone floor. Make sure the underside of the mat or rug is non-slip.
  • In restrooms and other wet areas, frequently squeegee off excess water to minimize soap scum and hard water deposits.
  • Apply a penetrating sealer to vanity or counter tops to minimize water spotting. If a stone countertop is meant for food preparation, make sure the sealer is non-toxic and safe for use on such surfaces.
  • Blot spills immediately with a paper towel. Don’t wipe; that will spread the spill. Flush the area with plain water and mild soap and rinse several times. Dry with a soft cloth. Repeat as necessary.

For general cleaning, contractors can use a neutral cleaner, stone soap or a mild liquid detergent and warm water.

Use a clean rag mop on floors, and a soft cloth on other surfaces. Rinse the surface thoroughly, and change the rinsewater frequently. Do not use scouring powders or creams.

Stain removal
If, after following the above tips, a stain persists, try to figure out what it is before trying more harsh techniques:

Oil-based stains typically will darken the stone. Clean gently with a soft, liquid cleanser.

Organic stains, including fruit, coffee, animal droppings or leaves, may cause a pinkish-brown stain, and may disappear once the source of the stain has been removed. Outdoors, once the sources have been removed, normal sun and rain will generally bleach out the stain. Indoors, use a 12 percent hydrogen peroxide solution, and a few drops of ammonia.

Biological stains, such as algae or mildew, can be removed with a 1/2 cup of ammonia, bleach or hydrogen peroxide, diluted in a gallon of water. (Do not mix ammonia and bleach.)

To remove ink stains, use bleach or hydrogen peroxide on light-colored stone, or lacquer thinner or acetone on dark stones.

Small amounts of paint can be removed with a lacquer thinner, or scraped off with a razor blade. Heavy paint coverage should be removed with a commercial paint stripper.

Water spots, surface scratches and nicks can be buffed with dry, 0000 steel wool.

If problems persist, try a poultice.

Metal stains, such as iron or rust, usually result from nails, flower pots and metal furniture. Copper and bronze stains appear 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.

Making and using a poultice
Some commercial stone-care manufacturers offer poultices. A poultice is a liquid cleaner or chemical mixed with a white absorbent material to form a paste about the consistency of peanut butter. Spread the poultice over the stained area to a thickness of about a 1/4 to 1/2 inch; cover with plastic and let it sit for 24 to 48 hours. The process may need to be repeated to remove a stain, but some stains may be permanent.

Poultice powders can include kaolin, fuller’s earth, whiting, diatomaceous earth, white molding plaster, chalk or talc. Do not mix whiting or fuller’s earth with acid chemicals. One pound of prepared poultice will cover roughly one square foot.

Here are some basic poultice recipes:

Oil-based stains: Use baking soda with water, or one of commercial powders with mineral spirits.

Organic stains: Use a commercial powder with 12 percent hydrogen peroxide or acetone.

Iron stains: Use diatomaceous earth and a commercial rust remover.

Copper stains: Use a powder and ammonia.

Sometimes, stains become permanent; in that case, a professional may need to repair or replace the stone.

Information courtesy of the Marble Institute of America, a professional organization of stone manufacturers, vendors and maintenance companies based in Columbus, Ohio.




POSTED ON: 11/1/2001