Understanding Stone TypesIn order to care properly for stone installations and preserve their natural beauty, it is important to understand how stone is created. Different types of stone have unique, complex mineral compositions which affect density, porosity, hardness and absorption rates. Stone is categorized in two ways - by its mineral composition, and by its geological formation, both of which affect its properties. All stone used for commercial purposes is eithersiliceousstone, orcalcareousstone. Siliceous stone is made of silica, Earth's most common mineral. Siliceous stone is very hard, very durable, and easy to maintain. Calcareous stone is the second-most-common mineral group, and is softer and more porous that siliceous stone. It is also durable but is sensitive to acids, some of which are found in common household cleaners.
There are three categories of geological stone formations; each is formed above or below the Earth's surface through different processes over millions of years. These categories are igneous stone, sedimentary stone and metamorphic stone.
A very hard stone, granite is prized for its high density, low porosity and ease of maintenance. However, granite does have microscopic cracks and fissures between its crystals that make it susceptible to oil- and water-based stains, so proper sealing and cleaning is important.
Limestone is derived from seawater and contains minerals and ancient sea creatures. Its texture varies from medium to fine, and generally does not exhibit much graining or crystalline structure. Limestone varies in hardness and is highly porous, making it more susceptible to staining than most other commonly-used stone.
Travertine is a variety of limestone and marble that contains holes formed by pressure, heat and water. These holes are usually filled with resin or other fillers during the fabrication process to create a flat, polished surface, but sometimes travertine is "tumbled" instead to give it a slightly rough old-world appearance.
Finishes Make a DifferenceThe type of finish applied to stone during the fabrication process has a significant effect not only on its final appearance, but also its porosity. Three of the most popular finishes are polished, tumbled and honed.
Polished stone has a very glossy, reflective surface. Its smooth finish brings out the grains and brilliant colors in the stone's crystals, and also reduces porosity. The shine comes from the natural reflection of the stones crystals, and can wear away if subjected to heavy foot traffic and improper maintenance.
Stone with a flat matte or low sheen gloss has a honed finish. Its surface is very smooth, but without the high gloss and vibrant colors characteristic of a polished finished. Honed stone is highly porous and suitable only for low-traffic areas or aesthetics.
Under powerful magnification, it's easy to see the differences in stone types and finishes.
Proper Care Maintains Both Beauty and ReputationsAfter examining these vast differences in types of natural stone and stone finishes, it is clear why specialized care is necessary for optimal results. Each stone reacts differently to the chemical formulas of sealers and cleaners.
Water-based sealers are easy-to-use, non-flammable and contain no toxic fumes. However, solvent-based sealers can be flammable and hazardous - be sure to select a water-based sealer.
General purpose sealers contain various sealing molecules that will penetrate and bond, but some won't and will simply be washed away. An ideal sealer is formulated with the right amounts of molecules to chemically bond with specific stone types and finishes, providing maximum protection.
Common household cleaners should never be used on stone as they often contain acids or harsh solvents that can erode the stone or etch its finish - ruining the stone completely. The acids can also create larger pores in the stone which increases the potential for staining.