The first step in proper stone care and maintenance is to understand your stone’s geological classification and composition. This information will help you to identify what cleaning products to use and how best to care for your natural stone.
Natural stone is categorised into three basic geological classifications by their respective formation processes
Additionally, stones in each category can be either Calcareous or Siliceous.
Calcareous stone is composed mainly of calcium carbonate, a chemical compound commonly found in natural stone, shells and pearls. Calcium Carbonate is sensitive to acidic solutions so mild, non-acidic cleaners are recommended.
Siliceous stone, as the term implies, is one composed primarily of silicates, such as quartz, feldspar, mica, etc. As such, a siliceous stone is generally resistant to most acids found although acidic cleaners are still not recommended, as these stones may contain trace levels of minerals that are acid sensitive.
The following chart is a helpful guide:
To get the longest life and to preserve the beauty of natural stone, follow these simple tips:
Dust Mopping: Dust mop interior floors frequently using a clean non-treated dry dust mop. Sand, dirt and grit are abrasive and can damage natural stone.
Mats/rugs: Entrance matting systems or area rugs inside and outside an entrance will help to minimise the sand, dirt and grit that may otherwise scratch the stone floor. Be sure that the underside of the mat or rug is slip resistant.
Vacuum cleaners: If used, be sure the metal or plastic attachments or the wheels are not worn as they can scratch the surface of some stones.
Spills: Blot the spill with a paper towel immediately. Don’t wipe the area, it will spread the spill. Flush the area with water and mild detergent and rinse several times. Dry the area thoroughly with a soft cloth. Repeat as necessary.
- Clean stone surfaces with a neutral cleaner or stone soap and warm water.
- An excessive concentration of cleaner or soap may leave a film and cause streaks. Follow manufacturer recommendations.
- Rinse the surface thoroughly after washing with detergent or soap solution and ensure the floor is dried.
- For large areas such as entrance lobbies, corridors etc use a scrubber drier that will wash, scrub and dry in a single pass.
- For even larger outside areas, a ride-on scrubber drier can be employed which will also be a more productive means of cleaning large areas.
- In outdoor pool or patio areas, flush with clear water and use mild bleach solution to remove algae or moss.
- Many suppliers offer products used for stone cleaning.
- Products containing lemon, vinegar or other acids may dull or etch calcareous stones.
- Scouring powders or creams often contain abrasives that may scratch certain stones.
- Many commercially available rust removers (laundry rust stain removers, toilet bowl cleaners) contain trace levels of hydrofluoric acid (HF). This acid attacks silicates in addition to other minerals. All stones, including granite and quartzite, will be attacked if exposed to HF.
Sealing is a common step taken on some stones as an extra precaution against staining. In fact, the sealing products used in the stone industry are ‘impregnators” which do not actually seal the stone, but more correctly act as a repellent rather than a sealer.
Sealing does not make the stone stain proof, rather it makes the stone more stain resistant. When consulting with your stone supplier, you may find that many stones do not require sealing. However, applying an impregnating sealer is a common practice.
When considering sealing, remember that sealing the stone does not make the stone stain proof, it makes it more resistant to staining.
If a sealer is applied in a food preparation area, be sure that it is non-toxic and safe for use.
Consult with your supplier or sealing manufacturer specific to the type of sealer and frequency of use recommended.
Stain Identification Tips
Identifying the type of stain on the stone surface is the key to removing it. Stains can be oil based, organic, metallic, biological, ink based, paint based, acid based. If you don’t know what caused the stain, consider likely staining agents that may have been present. Here are some questions you should consider:
Where is the Stain Located?
- Is it near a plant, a food service area, an area where cosmetics are used?
- What colour is it?
- What is the shape or pattern?
- What occurs in the area around the stain?
Stain Removal Steps
Surface stains can often be removed by cleaning with an appropriate cleaning product.
What Type of Stain is it?
The following sections describe the types of stains you may have to deal with and the appropriate household chemicals to use and how to prepare and apply a poultice to remove the stain.
Oil-based (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. Clean gently with a soft, liquid cleanser.
Organic (coffee, tea, wine, 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, sun and rain action will generally bleach out the stains. Indoors, clean with a mild hydrogen peroxide solution.
Metallic (iron, rust, copper, bronze) Iron or rust stains are orange to brown in color and follow the shape of the staining object such as nails, bolts, screws, cans, flower pots, 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.
Deep-seated, rusty stains are extremely difficult to remove and the stone may be permanently stained.
Biological (algae, mildew, lichens, moss, fungi) Clean with a recommended cleaning solution, generally containing ammonia, bleach, or hydrogen peroxide.
Paint Small amounts can be removed with lacquer thinner or scraped off carefully with a razor blade. Heavy paint coverage should be removed only with a commercial “heavy liquid” paint stripper available from DIY stores and paint centres.
These strippers normally contain caustic soda. Do not use acids or flame tools to strip paint from stone. Paint strippers can etch the surface of the stone; re-polishing may be necessary.
Follow the manufacturer’s directions for use of these products, and flush the area thoroughly with clean water. Protect yourself with rubber gloves and eye protection, and work in a well-ventilated area. Use only wood or plastic scrapers for removing the sludge and curdled paint. Normally, latex and acrylic paints will not cause staining. Oil-based paints, linseed oil, putty, caulks and sealants may cause oily stains.
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. When the smoke is removed, there may also be some etching (due to carbonic & other acids in smoke). Commercially available “smoke removers” may save time and effort.
Etch Marks (caused by acids left on the surface of the stone) Some materials will etch the finish but not leave a stain. Others will both etch and stain. Contact your stone dealer or call a professional stone restorer for refinishing or re-polishing etched areas.
Efflorescence (a white powder that may appear on the surface of the stone) It is caused by the deposition of mineral salts carried by water from below the surface of the stone. When the water evaporates, it leaves the powdery substance.
If the installation is new, dust mop or vacuum the powder. You may have to do this several times as the stone dries out.
Do not use water to remove the powder; it will only temporarily disappear. If the problem persists, contact your installer to help identify and remove the cause of the moisture.
Scratches and Nicks Slight surface scratches may be buffed with dry 0000 steel wool. Deeper scratches and nicks in the surface of the stone should be repaired and re-polished by a professional.