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Using Natural Stone

There are many types of natural stone that the construction building industry uses.

It's important for masons and mason contractors to be knowledgeable about each stone that they work with and understand how each type was formed, what types of minerals and natural elements are present behind the rough exterior, each one's characteristics, and how each might be used to its best advantage in building construction.

While obviously space prohibits us from discussing all the various individual types of natural stone available, here are three of the main subsurface natural stones used in the U.S. building industry:

Granite
Granite is a very hard natural igneous rock formation of visibly crystalline texture, formed essentially of quartz and orthoclase or microcline, and used especially for building and for monuments. It is made up mostly from a mixture of quartz, feldspar and mica. Granite has large crystals that can be seen very easily — the black specks in the material are crystals of mica.

The word "igneous" is from the Latin word ignis and means fire. Igneous rocks were formed from magma or lava. Magma is molten (i.e., melted) rock under the earth's surface. At the point when magma reaches the surface, it is called lava.

When the magma comes out of the earth's crust through a volcano as lava and is exposed to the surface elements, it cools and hardens, producing the more porous and less dense stones, such as pumice. This type of igneous stone is called "extrusive."

If the magma cools and hardens inside the earth, it is called "intrusive" rock. This rock cools slowly and has large crystals. When the magma does not reach the earth's surface, it is formed into a variety of geological structures. This intrusive type of stone is what is typically used as building stone. It is quarried from beneath the earth's surface and it comes in a variety of types, such as granite, basalt and obsidian.

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Photo courtesy of Buechel Stone Corp.

Limestone
Limestone is a rock that is formed chiefly by accumulation of organic remains (e.g., shells or coral) and consists mainly of calcium carbonate. It is extensively used in buildings throughout the United States.

Limestone is a very strong and durable material when used in the construction of buildings. It is especially popular in architecture, and many landmarks around the world, especially in North America and Europe, are made primarily of the material. Limestone is readily available and relatively easy to cut into blocks or more elaborate carving. It is also long lasting and stands up well to exposure.

Limestone was most popular in the late 19th and early 20th centuries — train stations, banks and other structures from that era are often limestone. It is used as a facade on some skyscrapers, but only as thin cladding rather than solid structural blocks.

Also, although limestone is readily available and quarried in the United States, other varieties are often imported from both Europe and Asia.

Limestone has long been known to be one of the best, high-quality building materials available for use today.

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Photo courtesy of Buechel Stone Corp.

Marble
Marble is limestone that is more or less crystallized through metamorphism, with the crystals ranging from granular to compact in texture. Marble is extensively used for sculpture, as a building material and in many other applications.

Marble is a metamorphic rock that, at some point, has undergone a metamorphism from limestone, composed mostly of calcite (a crystalline form of calcium carbonate, CaCO3). The word "marble" is often colloquially used to refer to many other stones that are capable of taking a high polish.

Marble is a very strong building material and can be polished to a beautiful luster. Marble has a very appealing finish when polished, and is found in many different sparkling colors such as white, pink, gray, red, yellow or black.

Spain is one of the largest producers of high-quality marble. It is imported to the United States for all types of building projects, and it is a very good building material.

Tips for Using Natural Stone
As with most masonry materials, it's very important for mason contractors, masons and architects to understand the qualities, hardness, porosity and other characteristics of the natural stone materials being used in each project. It's also important to follow some simple tips when using this natural product.

   
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Photo courtesy of Buechel Stone Corp.
"The best thing that mason contractors can do is know the type of stone they're working with," said Tom McNall, president of Great Northern Stone in Huron Park, Ontario. "Too many times — and I'm not trying to pick any fights here — they'll treat brick the same as they treat granite, the same as they treat limestone, because it's essentially a material cut into a block and they're putting it up on the same wall.

"Now granite won't scratch as easily as a marble or limestone; brick won't react with acids as, for instance, marble will," he continued. "The best thing that we can advise is to get to know the product that's coming in and get to know the limitations."

There are also some general tips that mason contractors and their crews should keep in mind when working with natural stone.

"I think one of the biggest things is to make sure you have an adequate foundation to support the stone," said André Hagadorn, Adirondack Natural Stone, Whitehall, N.Y. "Typically, full-size stone veneer is three to five inches thick, so you'll have to have a special foundation or ledge when you're starting a natural stone project."

If a project gets behind schedule, sometimes mason contractors will try to speed things up by having quarries ship cut stone as soon as it's completed. Rick Schneider of Buechel Stone Corp. in Fond du Lac, Wis., said this is not necessarily the best option to pursue.

"It's important to understand that a stone quarry cuts by yield, not by how it's going to get put up on the structure," he said. "So, as a stone quarry, we want to complete all of the cut stone prior to shipping any of it. We want to make sure the whole thing is complete and then ship it out that way, versus sills first, windows and so on."

He also recommended that mason contractors be mindful of the cleaning techniques used once the project is completed.

"You always want to clean the stone with soap and water first, not using any kind of pressure sprayers — at a very low volume, it might be OK, but that's where the discrepancies comes in," Schneider said. "You can't have that nozzle turned on high, because you can dig into the stone and actually peel off some of the stone with that high pressure. That's why we don't recommend a power sprayer, because you can get carried away with how strong they use it on it.

He also stated that acidic cleaners should be avoided because "acid can eat into the stone and take away some of the color."

A high-quality sealer can go a long way to protect some building stones, while also enhancing that natural color.

"On an absorbent stone, it might be good to use a sealer that goes into the stone and doesn't allow moisture to absorb into it," McNall said. "However, a lot of stones have very little absorption, so putting a sealer on them could actually cause problems."

McNall said that mason contractors can apply a very simple test to check a stone's ability to absorb water. "All you have to do it put a little water on the stone for ten minutes and if it doesn't go dark on the surface, then it's not going to absorb much water."

He also advised that mason contractors shouldn't make assumptions about hardness and porosity just because the material is a certain type of stone. "The stones that are commercially sold as granites, can be anywhere from six — I've seen some go all the way to five on MOHs scale of hardness — all the way to nine, so they can vary considerably."

No matter what the characteristics, when treated properly, natural stone's beauty will last a lifetime and beyond.

"Natural stone has really come a long way and is getting quite popular again," Hagadorn said. "It's really hard to beat a natural product that will last a long time."







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