My marble needs to breath!?!

For these and other mysteries, I thought you might benefit from my thoughts on the subject. One thing about this industry is, knowledge is hard to come by, and never written down . . . one of the reasons I decided to start a newsletter 7 years ago. “Breathing stone” and “lime-pops” were two of the most annoying phrases I regularly heard people use, yet no-one could tell me what they meant. Now I know.

First, limestone, under certain conditions, releases Carbon Dioxide (breathing). Limestone began as shells & bones of ancient sea life (see below!) that settled on the bottoms of now dead seas. The calcium in these shell & bones mixed with the Carbon Dioxide in the water to form Calcium Carbonate, the chemical basis of limestone & marble. Amazingly, most of the world’s Carbon Dioxide is locked up in limestone & marble, and if it were all released, you & I would suffocate. Good thing our products don’t breath too much, or we wouldn’t! (Mars, amazingly, has an atmosphere over 90% carbon dioxide, which may indicate what our original atmosphere was like before primitive sea life formed . . . we may owe a lot to the little guys!)

When limestone or marble gets wet, as it always does in our business, it can release some of this carbon dioxide. How does this interest me, you ask? First, the manufacturers of sealers know all about this, and have to allow just enough gas permeability in their sealers to let the carbon dioxide through. Another good reason why polyurethane isn’t such a good idea.

An example of what can happen when the carbon dioxide gets trapped are the Saltillo paver “lime-pops”. I was in Saltillo in Mexico a year and a half ago, and in standing in the dry river beds - called arroyo’s - I could look up high above the clay deposits and see limestone cliffs surrounding the valley. When the torrential rains of the region do fall, they wash granules of limestone down into the valley, which then get mixed into the clay, and ultimately contaminate the tile. Saltillo pavers are unglazed clay, so they absorb the moisture of the setting bed, as well as when washing off grout, mopping the floor, etc. This releases the carbon dioxide from the limestone granules. When the carbon dioxide tries to expand, but is encased in fired clay, pressure builds up - until the tile can hold it no more - hence the “pop”.

Amazingly, there is evidence that the affect water has on limestone, and its metamorphic equivalent, marble, is enhanced by the use of ground water (as opposed to distilled water). That is, un-pure water containing organic amino acids, which are obtained by life found in soils or the sea. It is possible that pure distilled water would lessen this effect . . .I will keep you posted in my next newsletter . . .