Page 17 - Demo

Slippery Rock Gazette
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Maintenance Corner
Maintenance Corner
A Basic Geology Guide for Stone & Tile Pros
I’ve been in the stone industry for well over 45 years. I have taught the res- toration and maintenance of natural stone, terrazzo, concrete, and ceramic tile for almost 40 years, and yes, I’m getting older, LOL! I was taught about the geology and chemistry, as it relates to natural stone, from both German and Italian engineers and technicians. 40 years ago, it was more straight forward than today as there was little to no engineered stone in the market- place, much less the new porcelain prod- ucts. Polishing concrete was a new and up-and-coming thing. There was no such thing as a purple (epoxy) terrazzo or porce- lain countertops (solid tops, not from tiles).
It is imperative to understand the charac- teristics of natural stones and how they are formed and what minerals they contain in order to restore, protect, and maintain them correctly. If you do not understand the basics in chemistry and geology regarding the stones, you will never understand why we use different chemicals, and do certain things on different materials. So bear with me and let’s dive into it.
Bob Murrell
M3 Technologies
Photos by Bob Murrell
Engineered marble. Note the minor surface scratches.
Above: Porcelain center island. Horizontal and vertical pieces are 1/2 inch with a 45° miter joint to appear like thicker material.
A drop of hydrochloric acid on marble (top picture) and on granite. Note that on the marble, the acid effervesces, and on the granite the acid has no reaction.
There are three basic types of natural stones: sedimentary, igneous, and met- amorphic. Sedimentary stones are com- posed of layers which are settled upon each other over time. Igneous stones are com- posed of previously molten minerals or lava. Metamorphic stones are either of the first two categories which have then been folded and compressed over time by enor- mous amounts of heat and pressure. It is fair to say that most stone with veins or considerable movement are metamorphic. Limestone that has been metamorphosed eventually becomes marble. Granite that has been metamorphosed becomes gneiss.
Marble, limestone, onyx, alabaster, trav- ertine, terrazzo (both cementitious and epoxy-based), and concrete/cement are some of the materials that contain cal- cium. At the most basic level, there are two groups of stone in the world, those that consist of mostly calcium and those that do not. This is an extremely important concept to grasp. By understanding this, we can
Marble countertop with etching all over the surface.
proceed to the procedures for each group. Calcium carbonate is a metal salt (20 on Periodic Table) and very sensitive to acids. To test if calcium is present in a stone, sim- ply place a drop of acid on the stone (in an inconspicuous area!). If the drop of acid effervesces (fizzes), the stone contains cal- cium. This is an etch. All calcium-contain- ing stone will etch if subjected to an acid. The stronger the acid, the faster and deeper the etch. On metamorphic stone containing ample amounts of calcium, we can actually use acids to accelerate the polishing pro- cess. Most polishing products for marble and calcium-based stones contain a spe- cific acid combined with micro-abrasives, which aids in producing a glass-like finish on the surface. Majestic 5X Gold is known as one the world’s best marble polishing
powders.
Calcium-containing stone is generally
softer than non-calcium containing stone, as well. Marble and limestone are some- where between 3-4 on the Mohs hardness scale, while granite and similar stones are around a 7 on the Mohs scale. You can do an in-field test using a knife blade to see if the stone will scratch (test in an incon- spicuous area!). The knife blade (steel) is around a 6.5 on the scale. The rule is it takes a higher number to scratch a lower number. The knife blade, at a hardness of about 6.5, will scratch marble (hardness of 3-4), but will not scratch the granite (hard- ness of about 7).
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