So...You Want to Clean and Protect Stone?

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So...You Want to Clean and Protect Stone?

By Dane Gregory, CEO 3M Corporation

There are many ways to make money in the cleaning business and stone cleaning and protection is one of the most profitable. However, there is a price to pay for that privilege. One must study the types of stone available in the marketplace and also learn the requirements of those stone types. Also, it's great to have some information on grout.

There are many stone types that can be used by designers and architects for flooring, wall coverings, bath vanities, shower walls and counter tops. Limestone, marble, travertine and granite seem to be the most popular choices, but there are many other stone types to be aware of. Identification of each type is paramount to making sure there are no cleaning problems. Let's look at several.

Limestone: Limestone is a sedimentary, calcium-based stone, which is sensitive to acidic products, not just cleaning products, but acid based beverages and fruits. Most limestone is fairly absorbent and can be stained by liquid spills. Limestone is typically finished by honing, meaning it has a smooth, but dull surface. Cleaning requirements call for a check of the stone and stone cleaning agents to assure that there no bad reactions from the products. Acidic cleaning products can etch the limestone surface causing damage to the finish, and dull spots that are visible in certain light.

Marble: Marble is a metamorphic, calcium based stone, which is also sensitive to acidic products. Many marble stones are absorbent and liquids can be absorbed into the capillary structure of the stone. The capillary structure is the area inside the stone that allow liquids to penetrate. The capillaries were created when the stone was formed geologically millions of years ago. Marble is usually finished by polishing the surface with diamond abrasives to leave the marble with a glass-like finish with an great reflective shine. The shine is created by polishing the minerals in the marble to a reflective shine with the abrasive, usually diamonds. The crystals in the minerals cause the surface to become reflective. Marble can also be finished by honing, as in limestone above. It can also be finished by tumbling, giving the marble a very distressed appearance. The tumbling removes any sharp edges and gives the stone the appearance of being very old and worn. Cleaning marble can be challenging because any acidic products can etch the stone surface, causing damage and dull spots that are visible in certain light.

Travertine: Travertine is also a sedimentary; calcium based stone and can be damaged by acidic products, as in limestone and marble above. Many travertine species can be absorbent and liquid spills can cause stains under the surface. Travertine is usually honed for a finish concept, but the stone contains voids or holes in the surface, and sometimes all the way through the stone. These voids can be a maintenance headache, as they will be filled with a polyester resin if the travertine is polished, or with grout if the travertine is honed. The grout will fill the voids as the travertine tile is installed. The fill used in the voids can be removed by heavy traffic, improper installation techniques or by improper cleaning techniques. If the fill is removed, it can cause real problems for the maintenance manager. The fill will be replaced by soil and the soil will be difficult to remove from the voids, as the voids will be lower than the rest of the surface.

Granite: An igneous stone of volcanic origin, granite is the hardest of all common building stone. It has minerals that will not scratch with a steel knife, making granite an excellent selection for counter top surfaces. Some species of granite, even though extremely hard, can still have a large capillary structure, which will allow liquid penetration. This can cause the granite to stain if the stone is not properly protected. Granites can be finished by polishing with diamond abrasives, honed to leave the surface with no shine, but a flat smooth finish, or a number of other popular finish types. Granite can be flamed to give the surface a very rough texture, which can trap soils and make routine maintenance a nightmare.

Stone Maintenance
Stone maintenance should take into consideration the absorbent tendencies of some stone. An easy way to find if the stone is absorbent is to place some water on the stone and observe if the minerals begin to darken in the area the water was placed. If absorbent, care must be exercised in the amount of water used in the cleaning process. Too much water can cause the stone to have some "downstream" issues such as efflorescence. Efflorescence is a mineral salt that will appear on the stone tile or along edges of the grout. The efflorescence comes through the capillary structure of the stone, drawn by the evaporation process. As the moisture evaporates, the mineral deposit is left on the surface. Wet cleaning with acidic products will remove the surface minerals, but the moisture used in the process will bring more minerals to the surface. Using low moisture cleaning techniques will minimize the potential of efflorescence. Any maintenance discussion will also have to include the issues of chemical sensitivity on some stone. Most calcium based stones are sensitive to acids and acid based cleaning products. The use of neutral and alkaline cleaning agents is required on these stone types. Granite is usually not acid sensitive, but you should test the surface to see if there is a negative reaction (etching).

Grout
The fill in the space between the stone tiles is made from grout. Grout in its simplest form is a cement mixture with a color pigment. A cement mixture hardens though a hydraulic process, not moisture loss. Once the grout hardens and cures, it becomes concrete. Concrete is extremely absorbent and liquid spills can cause discoloration and stains. Grout also has a capillary structure from the curing process, which is what makes it so porous. Cleaning concrete is a difficult task in its own right, but add the fact that most grout channels are lower than the tile surface give the soils a channel or groove to settle in. Routine cleaning procedures designed for flat floor surfaces simply do not work in this instance. Dust mops leave soils in the grout channel and if we have added dust mop oil to the mop, we will also leave traces of oil in the concrete channel. Damp mopping will also leave soil behind in the grout joint. This accumulation of soils, which include protein (organic) based soils and inorganic soils. Organic soils are displaced or emulsified with alkaline based cleaning agents, but the inorganic soils are best removed with an acidic cleaning agentThe acidic agent will not emulsify the inorganic soils, but etch the concrete on a microscopic level, causing the soils to be flushed away with the surface of the grout. Obviously, this is not a cleaning technique that should be used as a routine cleaning procedure, but dirty grout is a unique problem and one that plagues cleaning professionals every day.

Knowing the basics of the stone and grout is the most important information a cleaning professional can use to make good decisions on cleaning procedures, techniques and detergents. More information can be acquired by attending an IICRC Stone, Masonry and Ceramic Tile Cleaning Technician (SMT) class.