Getting To Know Your Stone – Limestone

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Limestone is a sedimentary rock originated in several possible environments, but with one factor in common: they are the sedimentation of organic matter, mostly calcareous skeletons of marine organisms. Its main component is calcium carbonate (CaCo3), commonly dubbed calcite. Typical additional components include: dolomite and aragonite. Also, varying amounts of clay, silt, sand, chert or flint can be found in limestones.

Limestone’s texture varies considerably, from compact and almost porcelain-like (commercially this type is traded as marble), to coarse and medium grain size. The latter MBStoneCare_AD2represents the majority of the dimensional stones commercially traded as limestone, and the focus of this little analysis. The range of colors varies from whitish, to yellowish, light brown, pink, red and sometimes also dark brown or almost black (if it contains bitumen due to the decomposition and transformation of the soft parts of the organisms which originated them).

The most popular kinds of limestones used as building materials are found in the USA, particularly in Indiana. Some other types of North American limestone are crystallized enough to be polished to a low, medium, and high gloss. They are mostly used for ornamental purposes (indoor cladding and flooring). Other popular limestone is available from France, Spain, Portugal, Germany, Italy, and India.

Now that we are through with the scientific make-up of limestone, let’s see what’s good and bad about this stone in general – making reference to its use in residential projects. One good feature about limestone- it is attractive. Limestone is mostly calcite and, as such, is extremely sensitive to harsh chemicals, particularly of an acidic nature. In layman language, limestone naturally neutralizes acids by giving itself up. Looking at this fact from the other side, acids – any acid- corrodes limestone. Since most foods are acidic, the employment of limestone in a kitchen should be considered as a chancy proposition (dolomitic limestone – also referred to as dolostone – is more acid resistant though).

Another factor to be taken into consideration is that most limestone is very porous, hence highly absorbent. Please keep in mind that this analysis is about coarse and medium grain limestones – the stones that are commercially sold as limestone, that is. Compact limestones don’t make this list because they are traded as marble. Limestone could be up to three times more absorbent than the average marble and two times more absorbent than the average granite, which translates into easy and quick staining when liquids, or oily substances are spilled on it. Penetrating sealers (also referred to as “impregnators”) specifically designed for very porous materials can help minimize this problem, at least on a temporary basis. No penetrating sealer, however, can solve the problem related to harsh chemicals (corrosion- or etching- by acids), nor can they solve other problems often related to certain limestone, such as natural discoloration, “powdering”, crumbling, “bleaching”, efflorescence and spalling. Furthermore, “impregnators” themselves can be chemically delicate and can be altered by harsh chemicals, such as common household cleaners.

The most important factor to be taken into consideration is that limestone is just a name. This means that under the classification of limestone are stones which are actually limestone, but they aren’t formed the same way and under the same circumstances. Therefore, the final products can be – and in many cases are – miles apart from one another. They range from stones with an acceptable degree of density and hardness, to some other stones that literally crumble under the action of running water!

As in all calcite-based stones (and most other natural stones), specialty cleaning products for routine maintenance are a must!

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