Carbonate and Silicate Stones

Carbonate stones are less resistant to the abrasive consuming and chemically more reactive than silicate stones, therefore demanding rigid estimation for maintenance in case of façades, floors and high traffic areas. Silicate stones are more resistant to the abrasive consuming and chemically less reactive than the carbonate stones, demanding well-taken care concerning the stain produced by infiltration of liquids, specially when applying mortar and finishing settings.

As already related, resistance to the abrasive consuming is normally proportional to the hardness of constituent minerals of the stones by the scale of Mohs. The main constituents of marbles - calcite and dolomite - have 3 and 3,5-4 hardness respectively. Hardness of the main components of granites is significantly superior, mentioning the quartz (hardness 7), the feldspars (6) and iron-magnesian minerals (4 to 6).

So, the abrasive resistance of granites is higher, whenever the amount of quartzes is greater . Among the marbles, abrasive and chemical resistance is higher when the dolomite character (magnesia) is greater.

Under the physical and mechanical point of view, silicate stones appear to be far better than carbonate ones, for external coverings, floors and heavy traffic areas in general. Considering just the same, carbonate stones turn out to be the ideal specification for interiors, with restrictions to: floors of high traffic, service areas and especially to kitchen sinks. In towns along the maritime shores, the use of the carbonate rocks for façades and floors is strictly inadequate, in reason of the constant attack by the marine aerosol, which contains chloride acid and because of abrasiveness of the beach sands.

The crushing and flaming finishings, less slippery, are preferable to the burnished ones for pedestrian traffic external floors. However, both crushing and flaming procedures increase the specific surface of the treated face and produce microfissures, thus increasing the absorption of liquids and dirt impregnation; in these cases, by means of specific tests, use of sealant (hydro-oil-repellent products to render impermeable); on the other hand, it is never recommended the crushing and flaming of natural absorbing rocks.

Two recommendations are thus important: the use of two rocks with distinct resistances to the abrasion is inadequate - for example marble and granite - for one same floor, in a place of high pedestrian traffic. In this case, there will certainly be differential consuming by the length of time. The use of marbles must be prevented in case of stairs steps, under great volume of traffic, when these conditions will cause higher consuming and produce depressions in the center of the steps.

Technical studies on finishing of surfaces, sealant, cement, mortar, jointing, waxes, detergents and antiskid varnishing, aiming to establish norms and standards of application, adequacy, conservation, cleaning and restoration, are recommended for the best specification on use of natural rocks in coverings.