Natural stone refers to a variety of mountain born materials including Slate, Marble, Limestone, Travertine, Granite, and Sandstone. Each of these has slightly different properties. It's important to understand the characteristics of the type of stone flooring tile you are purchasing in order to determine whether it is appropriate for a specific location.
As you shop for natural stone tiles, these are the factors that you should question retailers about:
The absorption rating refers to how porous a given material is. The more absorbent it is, the more susceptible it will be to stains, as well as cracking damage in freezing conditions.
There are 4 levels of absorption that a tile can have;
Non-vitreous: This is the highest absorption level. In most cases non-vitreous tiles should not be used in any damp environment.
Semi-vitreous: While these tiles are less absorbent, the more liquid they are exposed to, the more maintenance they will require.
Vitreous: This is the standard absorption level for flooring tiles and these materials are generally considered appropriate for most low to mid traffic indoor and outdoor applications.
Impervious: These materials are resistant to the absorption of liquids and thus will be easier to maintain. They are often used in high traffic commercial applications.
Specific Tile Absorption Rates: In general, Sandstone is the most porous natural stone material, Travertine, Limestone, and Slate have medium absorbency, and Granite is relatively waterproof. Polished materials also absorb less water than honed or clefted surfaces.
Some retailers use a grading system to rate the quality of materials. This can refer to the size, shape, and thickness of the tile, as well as the condition of its surface. Most grading systems have three levels of quality. Grade 1 refers to high quality, uniform materials. Grade 2 consists of materials with minor defects such as chips, scratches, or irregular surfaces. Grade 3 materials have major flaws in size, shape, surface, or chipping, making them appropriate only as accent pieces, or in certain rustic decorative applications.
Coefficient of Friction
This measures how slippery various materials are. The higher the coefficient, the more traction a tile will have. This number is especially important in moist environments such as bathrooms and kitchens, as well as high traffic commercial areas. The Americans with Disabilities Act requires that flooring material have a minimum of a .6 dryness coefficient.
Indoor vs Outdoor Rating
Some natural stone flooring materials are more suited to outdoor applications than others. Many of the factors above will determine whether a material should be used in an open air environment. Non-vitreous materials will be subject to staining through dirt and acid rain, as well as cracking when absorbed materials freeze and expand. Stones which have a low coefficient of friction will also pose a slipping hazard during rain and snow storms.
Natural stone materials are formed beneath the earth over millions of years, and often contain a variety of disparate elements. Sometimes iron is present in these materials, which can manifest as bright red and amber hues in the surface of the stone. The problem in an outdoor environment is that, those traces of iron can oxidize, a process more commonly known as rusting. This can cause the entire tile to degenerate over time.
Benefits of Using Natural Stone Flooring
Each piece of stone is a unique creation of the earth, making every flooring application one of a kind.
The mountain born qualities of the stone can help to reconnect a space with the natural world.
While there is some debate about the ecological impact of quarrying and transporting stone materials, the tiles themselves are natural, nonpolluting, eco-friendly pieces. Purchasing stones which were acquired locally can cut down on the environmental impact of transport.
Drawbacks of Using Natural Stone Flooring
With the exception of Granite and some Slate, natural stone is quite porous, and needs to be treated with a sealing agent periodically to protect its surfaces.
Some polished materials such as marble can scratch easily.
Some stones are also very brittle, and will chip easily.
When purchasing natural stone flooring materials it is important to do your research and understand the characteristics of the material you are purchasing. You want to find out whether it will be appropriate for your specific application and how much maintenance it will require. Ask your retailer multiple questions, and get to know the material as much as you can before you make a purchase.