About Limestone

Like a number of types of natural stone, limestone has been used for a variety of projects through history. In this article though, we will not embark on a journey through the various architectural applications of limestone. Rather, we will simply talk about the material and its composition. Because it can be a challenge to understand how various materials relate to one another, we will also explain how it differs from other materials that are similar to it.

What Is Limestone?

Limestone is a sedimentary rock that forms via a natural process wherein calcite and aragonite (crystal forms of calcium carbonate) precipitate out of water that contains dissolved calcium. Limestone often contains fossils since oceanic environments have abundant water and aquatic life with bones, etc.

Limestone Differs From Marble (Scientifically)

Reading the explanation above, about what limestone is might lead some to believe that it is just another name for marble, which is a natural stone as well. And you may find stone professionals that consider them to be the same thing. However limestone is not the same thing as marble scientifically speaking. In fact, these types of rock are of two different types. Limestone is a sedimentary rock and marble is a metamorphic rock. Notice what a page on the USGS.gov website said about this:

"The main difference between limestone and marble is that limestone is a sedimentary rock, typically composed of calcium carbonate fossils, and marble is a metamorphic rock. Limestone forms when shells, sand, and mud are deposited at the bottom of oceans and lakes and over time solidify into rock. Marble forms when sedimentary limestone is heated and squeezed by natural rock-forming processes so that the grains recrystallize. If you look closely at a limestone, you can usually see fossil fragments (for example, bits of shell) held together by a calcite matrix. Limestone is more porous than marble, because there are small openings between the fossil fragments. Marble is usually light colored and is composed of crystals of calcite locked together like pieces of a jigsaw puzzle. Marble may contain colored streaks that are inclusions of non-calcite minerals."

So, from that explanation we see that marble is a natural rock that used to be limestone before the metamorphic process changed it to what it is now. Note though what Geology.com says about the naming and referencing actual limestone material in the stone industry (italics ours):

The name "marble" is used in a different way in the dimension stone trade. Any crystalline carbonate rock that has an ability to accept a polish is called "marble." The name is sometimes used for other soft rocks such as travertine, verd antique, serpentine, and some limestones.

Properties of Limestone

Now that we have established that some limestone could be called "marble", let's look at the properties of limestone. Natural limestone has a number of properties that contribute to its usage.

Limestone forms in a number of ways and because of this, there are many types of this stone. Each of the various types has its own name. Some of these include:

• Chalk - this limestone is very fine textured and is easily crumbled. Chalk is very light in color (usually white or gray).
• Coquina - is a poorly cemented limestone composed of sand-size fragments of shell and coral debris. Color can vary.
• Dolomitic Limestone - composed primarily of calcite, this limestone has had some of the calcite altered to dolomite.
• Fossiliferous Limestone - limestone that contains obvious and abundant fossils (usually marine invertebrates) is referred to by this name.
• Lithographic Limestone - this dense limestone has very fine and very uniform grain size. It separates easily ot form a smooth surface.
• Oolitic Limestone - formed by concentric accumulation of calcium carbonate layers around a nucleas such as a sand grain, shell fragment, or other small object. This limestone has a distinct speckled look due to the oolites (small, sand-size clasts of sphere or oval shaped calcium carbonate) of which it is made.
• Tufa - porous limestone produced by precipitation of calcium carbonate from the waters of a hot spring or other body of water.

In the list above, we have excluded another type of limestone called travertine because we have a page dedicated to travertine that goes into greater detail about this material.

How Limestone is Used

As we have seen in the above information, there are a number of kinds of limestone and when used in different forms, limestone can be used for a range of purposes. Some of these include:

• Dimension Stone
• Plastic Filler
• Roofing Granules
• Flux Stone
• Paper Filler
• Portland Cement
• Paint Filler
• AgLime
• Animal Feed Filler
• Lime
• Rubber Filler
• Safety Dust (Mining)
• Filter Stone

As you can see, there are a number of uses for this substance and they vary in their nature. Not every use for limestone is as practical as other uses. Let's look at some specific uses in which limestone is performant and in which fabrication plays a role.

Limestone Panels

Panels created from limestone are one practical use for this performant natural stone. Wall cladding and building facades are all applications for natural limestone panels. Panels can be polished, brushed, or finished in another manner. Its durability and beauty are well established through use over the years.

Limestone Tiles

Another use for limestone is as a floor tile material. These tiles might be used outside or indoors. Some environments are better suited for limestone tiles than are others. For example, limestone tiles are excellent for use as pool decking. Why is that? Well, wet environments like walking surfaces become slippery when water stands on them. The less porous the material, the more water will stay on the surface. Conversely, absorbent materials like limestone, which is porous, allow liquids to penetrate the material. If the water from a pool gets on a pool deck made from limestone tiles, it is easily absorbed by the limestone and does not stand on the surface. Therefore, walking on an unfinished limestone tile surface provides better traction than other surfaces. Even finished surfaces provide traction if they are rough or unpolished; like brushed, or antiqued finishes.

Fabricating With Limestone

Are there any specific things to keep in mind when fabricating limestone? Because limestone is composed of the same mineral as marble, it shares fabrication methods, processes, and tools with marble. Even though limestone is hardness of 3 or so on the Mohs scale of mineral hardness it does need to be cut using a diamond blade designed for cutting "soft" stone. Therefore, diamond marble blades are recommended for cutting limestone tiles, surfaces, and panels. In addition to fabrication specifics, there are some care and maintenance recommendations for decorative limestone surfaces and you are interested in maintaining it.

Care & Maintenance of Limestone

Caring for and maintaining limestone is not complicated. However, it will take time, energy, and expense. And although not all limestone requires all of these treatments, decorative surfaces that get used and that you want to be stain resistant, will benefit from the following three step care process:

1. Seal the limestone surface using a penetrating sealer so the surface will repel water based and oil based liquids.
2. Clean limestone surfaces treated with sealer using a cleaner that is formulated to clean limestone and other materials containing calcium carbonate.
3. If a stain occurs on a decorative limestone surface, use the appropriate stain remover to draw the stain out of the stone.

The three treatments above work together to maintain the limestone surface. If the incorrect cleaner is used on limestone surfaces, it will dissolve the stone since calcium carbonate is susceptible to acid. Additionally, if you find that a limestone surface is staining easily, it might be an indication that it needs to be sealed again. Finally, in outdoor conditions natural weather can require sealer treatments on a more regular basis.

Is Limestone Right for Your Project?

Ultimately, your decision to use or not to use limestone for your project is up to you. However, knowing a bit about the material and what kinds of things can be done with it will help you make the decision. As we have discussed here, limestone is used for many different applications and can make a great material for surfaces that regularly get wet or have the potential for standing water. Furthermore, knowing how to care for and maintain natural limestone will contribute to your getting the best from the limestone surfaces you choose.