Porosity and permeability are properties of natural stone that result from geological processes. In the absence of these properties, the appearance of onyx, granite, marble, quartzite, and other popular stone construction materials would be drastically different and perhaps not as visually appealing. In short, porosity refers to the void spaces on surfaces. Porosity can be measured by various means, and it can be expressed as a percentage or as a fraction between 0 and 1. Some types of natural stone are more porous than others. For example, limestone is very porous when compared to quartzite, and granite isn’t as porous as marble. To better understand the natural porosity of granite, it helps to understand the following details.
Granite Is an Igneous Rock
The general composition of granite includes silicon dioxide, feldspar, mica, and various minerals. Within the Earth’s mantle, granite forms deep below sedimentary layers, but it eventually ascends closer to the surface and can be extracted from quarries in mountain ranges that are orogenic in nature, meaning they’re high above the seabed. Granite is also metamorphic, which means it goes through changes caused by chemical reactions that cause it to rise and find cracks in the crust before the settling and emplacement processes. All igneous rocks are porous, and granite is no exception.
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Granite Is Less Porous Than Marble
Each pore on the surface of granite tiles or slabs is considered to be a microscopic void. The size of these tiny voids, along with their surface count, determine the porosity level. As previously mentioned, granite is of an igneous nature, which makes it less porous than sedimentary rocks such as limestone and travertine. In the case of marble, which is metamorphic as well as sedimentary, porosity can be considerably higher when compared to granite, up to 2 percent. Most granite blocks have porosity ratios that range between 0.4 and 1.5 percent.
The Low-Porosity Advantage of Granite
In New York City, the women’s bathrooms at the main Port Authority Bus Terminal were recently remodeled with long granite countertops to handle the heavy traffic of visitors who come in to do their makeup, and this stone was specifically chosen because its lower porosity makes it easier for attendants to maintain. White marble may have been a more elegant choice, but the prospect of such a surface becoming easily stained with face powder, lipstick, and mascara prompted the Port Authority to go with granite.
Porosity Calls for Sealing the Stone
Those microvoids on granite surfaces are the reason you should periodically apply a specially formulated granite sealer such as Granite Gold Sealer® to your granite floors and countertops. You don’t want acidic or caustic substances to seep through the pores and deposit beneath the surface, as this could result in stubborn stains or even etching. Even though granite isn’t as porous as other stones, it still needs to be sealed.
Like all of the products provided by Granite Gold®, Granite Gold Sealer® is safe to use on all types of natural stone, including marble, travertine, and slate. To learn how to seal granite and other types of natural stone, check out the wealth of information on our website and in our blogs, or give us a call today at 1-800-475-STONE (7866).
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