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Stone 101

Natural Stone Basics

The following was published in 2004 by the Marble Institute of America.

"Natural Stone: Building Blocks Through Time"

There are three primary geological classifications for natural stones used in construction applications. These classifications are igneous, sedimentary and metamorphic and reflect how the rock was formed.

IGNEOUS

Igneous rocks were molten matter deep in the earth; they cooled and took shape as the mass was pushed to the surface. Igneous rocks include granite, gabbro, basalt and porphyry. The mineral composition is primarily feldspar and quartz plus other minerals such as mica and hornblende that contribute to the color of the stone.

The grain structure can range from coarse to fine and is generally consistent throughout the stone, although some can show veining. Broad ranges of colors are available including reds, browns, blacks, whites, beiges, yellows, pinks, greys and greens. Granites are hard, dense stones that can be highly polished or finished in a variety of ways. They are generally suitable for exterior and interior applications.

SEDIMENTARY

Sedimentary rocks include limestones, travertines, sandstones and soapstones. They were formed by the accumulation of materials settling in basins and sea beds and becoming compacted over millions of years.

Limestones are a common building stone used throughout the world in colors ranging from grey to buff and some pastel shades of pink and yellow. Limestones are composed primarily of calcium carbonate. Some limestones are very hard and dense; others are softer and more porous. Harder limestones may take a polish while the softer ones will not.

Travertines are a crystalline form of calcium carbonate that developed in layered deposits adjacent to cold and warm mineral springs. The characteristic holes were formed by the percolation of the mineral waters through the deposit over millions of years. Travertines vary widely in hardness, density and porosity. They are typically light to dark beige although some have white to dark brown veining. Some travertines can be polished to a high gloss finish.

Sandstones are composed primarily of quartz crystals bonded together with silicon, calcium carbonate or iron oxide. The color of sandstone is determined by the amount of iron oxide present and the colors can range from light to dark including browns, reds, buffs and yellows. The density, porosity and hardness of sandstones will also vary depending on the specific quarry deposit.

Soapstones range in color from grey green to grey brown and are composed of talc and chlorite. The talc gives soapstone its characteristic slippery feel and makes it a very soft, but dense, stone that is used for ornamental carving. Its heat-retention qualities also make it appropriate for cladding for heating units.

METAMORPHIC

Metamorphic rocks include marbles, slates, quartzites, schist and gneiss. These rocks were formed as another type and over millions of years metamorphosed into the building stones with these familiar names.

Marbles are composed primarily of dolomite and calcite with a wide variety of other minerals contributing to the color and texture. Marble began as limestones and the colors, textures and veining are produced through metamorphic activity. A rainbow of colors from around the world is available including blacks, reds, pinks, yellows, whites, greens, blues and beiges. Commercially, any stone (except granite) capable of taking on a polish is called marble. However, a true marble is completely metamorphosized.

Slate is formed by the metamorphosis of clay and shale and is composed of quartz, mica chlorite. It is uniform in color and generally available in dark to light green, black, grey or dark red. Unless the surface has been honed smooth, slate can be recognized by its distinct cleft pattern.

Quartzite is compact and dense stone composed of quartz, mica and feldspar. It is metamorphosed sandstone and some can have a texture similar to slates.

Schist is further metamorphosed slate with a granular texture similar to granite. Some schists are marketed as bluestone. Gneiss is further metamorphosed schist. Gneiss-type stones are composed primarily of quartz and feldspar and are often confused with granites.

Serpentines are green in color and show banding throughout the stone. They are similar to marbles in character, but are composed of hydrated magnesium silicate. Serpentines are dense, but can be soft and difficult to polish to a high gloss.

Stone Maintenance

DO'S AND DON'TS

Do dust mop floors frequently
Do clean surfaces with mild detergent or stone soap
Do thoroughly rinse and dry the surface after washing
Do blot up spills immediately
Do protect floor surfaces with non-slip mats or area rugs and countertop surfaces with coasters, trivets or placemats
Don't use vinegar, lemon juice or other cleaners containing acids on marble, limestone, travertine or onyx surfaces
Don't use cleaners that contain acid such as bathroom cleaners, grout cleaners or tub & tile cleaners
Don't use abrasive cleaners such as dry cleansers or soft cleansers
Don't mix bleach and ammonia; this combination creates a toxic and lethal gas

Polished Interior Stone

Polished stone has a glossy surface that reflects light and emphasizes the color and marking of the material.

Polished interior stone has traditionally appeared as wall veneer. It is also seen in the form of furniture and desktops, counter and lavatory tops, tables, and other items of designer quality, as well as tiles for commercial and residential installation.

Normal "housekeeping" maintenance involves only periodic washing with clean, potable water and neutral (pH-7) cleaners. "Soapless" cleaners are preferred because they minimize streaking and filming. However, mild phosphate-free, biodegradable liquid dish-soaps, soap flakes or powders which contain no aromatics are acceptable if rinsing is thorough.

Stone surfaces should be first wetted with clean, hot (not boiling) water. Then, using the cleaner solution (following manufacturer's directions), wash in small overlapping sweeps, from bottom-up if a vertical surface. Rinse thoroughly with clean, potable water to remove all traces of soap or cleaner solution. Change the water in the rinse pail frequently. Dry with soft cloth or cotton-flannel, and allow to thoroughly air-dry. Chamois skin may be used in lieu of cotton cloth in this process.

Note that any flooring surface, regardless of how it is finished, is slippery when wet. Care should be taken to promptly remove liquids or foreign materials that might result in safety hazards before permitting pedestrian traffic.

Generally, prevention will save a great deal of time spent on cures and remedies, especially since damages to stone are often irreparable.

Polished stone should receive the same care and consideration that is given a fine wood finish. Spills of any type should be immediately removed and water-rinsed. Coasters should be placed under all glasses, particularly those containing liquors or citrus juices. Hot-plates should be used under heated dishes. And, place-mats or felt bottoms should be placed under china, ceramics, silver and bric-a-brac to prevent scratching of polished finishes.

See the "Stain Removal" section below for cases where nominal care and cleaning procedures have not been followed.

HONED INTERIOR STONE

A honed finish is a satin smooth surface with relatively little light reflection.

Generally, a honed finish is preferred for floors, treads, thresholds and other pedestrian traffic locations where heavy traffic would wear off a polished finish.

As a rule, honed finishes are more susceptible to soiling then polished finishes, because a honed surface is slightly more porous and absorptive than a polished finish. However, the honed finish is easier to restore because it will sustain harsher cleaning efforts.

Normal "housekeeping" maintenance of a honed finish involves as-needed washing with clean potable water and neutral (pH-7), mildly abrasive cleaners. Commercially available "Soft-Scrub®" or other thick liquid cleaners and chlorine-bleach type scouring powders are ideal for this purpose. Simply mix in clean water according to manufacturer's directions.

CAUTION: Bleach should not be used on dark colored stones because it may lighten their color.

Surfaces should be first wetted with hot, clean water. Then, using a mildly abrasive, alkaline cleaner and a medium bristle brush, wash in overlapping, swirling strokes. Suds build-up can be left to stand for several minutes to permit the bleaching agents to work on stains and dirt. On vertical surfaces, always work from bottom-to-top.

Rinse thoroughly then wipe dry with cotton, cotton flannel, burlap, or chamois skin. Wipe well to avoid streaks. If further cleaning is needed, make a paste to the consistency of syrup using a mildly abrasive alkaline cleaning powder and clean, potable water. Apply the paste uniformly over the surface with a broad brush and allow to stand until dry. Then, use a medium bristle brush with additional water and scrub the surface vigorously. (Additional cleaning powder may be added at this point.) Rinse thoroughly and dry as described above.

For honed stone used on furniture tops and the like, follow care practices as described above for Polished Stone.

Note that any flooring surface, regardless of how it is finished, is slippery when wet. Care should be taken to promptly remove liquids or foreign materials that might result in safety hazards before permitting pedestrian traffic.

Regular, daily mopping of traffic surfaces should be done as described in the "Stone Floors" section.

In areas where normal care and cleaning prove inadequate, see "Stain Removal" below.

STONE FLOORS

"Stone Floors" broadly include any honed finish stone that is a traffic surface.

The "Stone Floors" category includes treads, floors and thresholds.

Honed finish floors, treads, and thresholds subjected to traffic, should be regularly mopped or scrubbed in a manner that will not leave a hazardous, slippery film.

Stone surfaces should be first wetted with hot, clean water. Lightly sprinkle an abrasive cleaner (i.e.: a chlorine-bleaching type household scouring cleaner. Do not use bleaches on dark-colored stone) over the wet stone, or put one-to-two handfuls into a pail of 2-3 gallons of hot clean water. Using a scrubbing motion, mop the stone surfaces with this solution (or with clean hot water if cleaner is sprinkled directly on the stone). Rinse thoroughly with clean hot water and dry with mop or cloths. Power scrubbers (RPM less than 375) can also be used for cleaning as described above.

See "Stain Removal" for areas that do not respond satisfactorily to normal housekeeping procedures.

Often, it is desirable to protect special interior areas and to enhance the coloration of honed stone in areas where a polished finish is not practical. In such cases, sealers may be applied after the stone has been cleaned to minimize maintenance and prevent staining around toilets and urinals, and in food preparation areas or entrances.

Note that sealers should only be applied to clean interior stone, as the sealer will seal in any dirt on the stone. Follow the manufacturer's directions for application and subsequent maintenance.

Do not use soft-finish waxes, paste wax, or resins. These coatings collect dirt and grit. Some acrylic base, liquid floor "waxes" advertised as "non-yellowing" can be used in place of "permanent" sealers, but may give limited life. See the section below on "Sealing Stone" for more information.

Exterior Stone

"Exterior Stone" is a general term denoting a stone installed in a situation where temperature, moisture, and air-borne contaminants are regulated primarily or solely by the forces of nature.

Exterior stone can be used in a honed, textured, or a polished finish in any mode in an exterior environment. However, the use of a polished finish marble or limestone is discouraged for exterior applications due to susceptibility to damage by air-borne acids and wind-driven dust.

In accessible areas, routinely follow maintenance procedures as specified in the section for Polished Stone above, or the section for Honed Stone, as applicable.

The large expanses of stone traditionally found on exterior multi-story installations generally will make it impractical or uneconomical to perform housekeeping maintenance on a frequent basis. However, such large installations should be given periodic overall cleaning consistent with economy, or as necessary to remove accumulated pollutants.

The cleaning of multi-story installations should only be done by qualified contractors who have the craftsmen, equipment, resources, and technical expertise to execute the cleaning work properly, as well as perform any repair or resetting that may be found necessary during the initial inspection. Consult the listings of MIA Members to obtain the required services.

Generally, the processes used in multi-story cleaning will be similar to normal procedures except that pumps for wash and rinse water should be employed to economize on the amount of time required due to the inherent high costs of labor and support equipment necessary to the undertaking.

Specialty Finishes

Specialty finishes are surface finishes other than "polished" or "honed" and often are provided as specialty treatments under specific trade names. Such treatments usually are patented or copyrighted products of the supplying contractor.

Examples of such specialty finishes are polymer coatings, texturing treatments, and a variety of chemically-produced surface conditions.

Specialty finishes are provided to meet the requirements of service under which traditional polished, textured, or honed finishes prove inadequate, are subjected to unusual hazards, or do not satisfy the ever-broadening requirements of designers.

Examples of the applications of specialty finishes are polymer coatings for liquor-dispensing and food-service tops; or textured surfaces for special lighting effects, decor enhancement, graffiti resistance, and maintenance reduction.

Consult literature or instructions furnished by the supplying contractor for care and remedial measures pertinent to the specific specialty finish. (Always request this information when the installation is first made.)

Sealing Stone

PENETRATING SEALERS

The best way to improve stone's stain resistance is to apply a penetrating sealer, also known as an impregnator. Unlike waxes or other coatings, these sealers go below the surface and protect the stone from within.

Impregnators penetrate into the substrate creating a barrier resistant to water penetration, oil penetration, stains, decrease surface absorption, reduce wear, allow 100% vapor transmission, increase static coefficient of friction, without altering the natural look.

The premium sealers - such as Miracle Sealants' 511 product line contain a chemical known as a fluo-alphatic, which repels both water- and oil-based stains. Penetrating sealers that contain silicone repel only water. Visit the Stone Care product section of our web site for product-specific information. Manufacturer's Product Data Sheets and MSDS documents are available upon request.

Not all stone needs to be sealed. Some stone is so dense that staining isn't a serious problem. The test is simple: Just place a drop of water on the surface. If it doesn't darken the stone after several minutes, a sealer is optional. But if the area under the drop becomes dark, then the stone is porous and should be sealed.

The sealing process is quick and easy. Pour the sealer onto dry stone, or apply with a clean brush or cloth and let it sit for a few minutes; then remove the excess with a clean soft cloth. Reapply yearly, after the stone has been refinished or poulticed, or whenever it takes less than five minutes to absorb a drop of water.

Stain Removal

Adherence to normal care and maintenance procedures should help prevent staining. But, should accident or neglect contribute to staining, necessary remedial measures will be completely different from general cleaning and will usually require persistence to achieve results.

Marble, granite and natural stone are porous materials. This porosity is why some stones stain 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 classified into one of the following categories:

Oil-Based Stains: Grease, tar, cooking oil and food stains.
Organic Stains: Coffee, tea, fruit, tobacco, cosmetics, etc.
Metal Stains: Iron (rust), copper, bronze, etc.
Biological Stains: Algae, mildew, lichens, etc.
Ink Stains: Magic marker, pen, ink, etc.

There are, of course, other materials that will cause staining. but these five categories are the most common.

Poulticing Powders:

Clays (Attapulgite, Kaolin, Fullers earth)
Talc
Chalk (whiting)
Sepiolite (hydrous magnesium silicate)
Diatomaceous Earth
Methyl Cellulose

Clays and diatomaceous earth are usually the best. 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.

Many stains are so deeply imbedded that the poultice alone will not be completely effective. Some type of chemical solution will need to be added to the poulice. When the poultice and chemical are applied, the chemical is absorbed into the stone. The chemical reacts with the stain and is re-absorbed into the powder/material.

Stain Removing Chemicals

How do you choose the proper chemical for a given stain?

First, you need to identify the stain. This is the most important step in stain removal. If you know what caused the stain, you can easily look at a stain removal chart for the proper chemical to apply. If the stain is unknown, then you need to play detective.

Try to determine what caused the stain. If the stain is near a plant container, it might be that the plant was over watered and the soil has leached iron onto the stone. The color of the stain may help to identify the cause. Brownish color stains may be iron (rust) stains. The shape or the pattern of the stain may be helpful. Small droplet size spots leading from the coffeepot to someone's desk are a sure giveaway.

Do some investigating and use your powers of observation. This will almost always lead to the identification of the cause of the stain.

If, after thorough investigation, you still have no idea what the stain is, then you will need to perform a patch test. A patch test simply means applying several chemical poultices to determine which will remove the stain. There are also pre-prepared poltice mixes that have the chemicals already added. All you have to do is add water.

Stain Removal Guide

Iron (rust) - Poultice with Oxalic Acid + Powder + Water. May also try a product called Iron-Out (available at hardware stores). Both mixtures may etch polished marble, so re-polishing will be necessary.
Ink - Poultice with Mineral Spirits or Methylene Chloride +Powder.
Oil - Poultice with Ammonia+ Powder Methylene Chloride can also be used on tough oil stains.
Coffee, Tea & Food - Poultice with 20 percent Hydrogen Peroxide + Powder.
Copper - Poultice with Ammonium Chloride + Powder
Paint (water-based) - poultice with a commercial paint remover + Powder
Paint (oil) - Poultice with Mineral Spirits + Powder. Deep stains may require Methylene Chloride.

Once the stain is identified, the following steps can be followed:

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.
Prepare the poultice. If a 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. If a paper politice is to be used, soak the paper in the chemical. Lift the paper out of the chemical until it stops dripping.
Apply the poultice to the stain being careful not to spill any on the non stained areas. Apply the poultice paste to the stone with a wood or plastic spatula, approximately 1/4-inch thick over-lapping the stain area by about one inch. Insure the poultice is in full contact with the stone, with no entrapped air pockets or voids.
Cover the poultice with plastic (food wrap works great). Tape the plastic down to seal the edges with blue painter's tape. (Regular masking tape is too sticky and may remove sealer or even dull the stone surface when it's pulled up.) 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 poltice staying wet. 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. When the poultice is dry, remove the tape, and the plastic with it.
Remove the poultice with a wood or plastic spatula to avoid scratching. Rinse the cleaned area thoroughly with clean water; blot or wipe off excess water with a soft cloth and allow the work to dry. If the stain is not removed, apply the poultice again. It may take up to five applications for difficult stains. If there's a ring around the newly cleaned area, it's residual moisture that should evaporate within a few weeks. To expedite the drying process, sprinkle a bit of dried poultice over the spot. Some chemicals may etch marble and limestone surfaces. If this occurs, then apply polishing powder and buff with a piece of burlap to restore the shine.

Call your professional stone supplier, installer or restoration specialist for problems that appear too difficult to treat.

Disclaimer

Carved Stone Creations, Inc. does not manufacture installation products or stone cleaning/maintenance products. Carved Stone Creations, Inc. provides the information contained herein to its customers as an information source only. The products identified in this document may have chemicals that cause reactions in certain individuals.

Carved Stone Creations, Inc. strongly recommends the use of safety glasses, respirators (masks) and gloves in handling any materials that contain chemicals. Carved Stone Creations, Inc. recommends the proper disposal of any scrap stone/stone, installation and/or maintenance products discussed herein. Please contact the manufacturer directly, PRIOR to usage, to obtain proper handling instructions, application instructions and warning concerning potential health hazards for any product contemplated for use. Carved Stone Creations, Inc. also strongly recommends that you ALWAYS test a small area PRIOR to usage of any installation/stone/cleaning/maintenance product to determine whether the product you are about to apply serves its intended purpose.

By writing these instructions, Carved Stone Creations, Inc. in no way makes any warranty nor takes any responsibility for cleaning of the stone, stain removal or any other work. Further, these instructions are merely our suggestions on how to maintain the stone. Use at your own risk. Any warranty, representation, statement or undertaking whatsoever that may be expressed or implied by statute, custom or otherwise is hereby expressly excluded. Under no circumstances shall Carved Stone Creations, Inc. be liable for any costs, losses, expenses or damages (whether direct or indirect, consequential, special, economic or financial including any losses of profits) whatsoever that may be incurred through the use of any information contained in the Carved Stone Creations, Inc. website or in any other document.