Sedimentary
Sedimentary stone is created through cementing, consolidating, and crystallizing chemical solutions and biological deposits. Examples include sandstone and limestone—the latter of which has a primary mineral composition of calcite and dolomite. Limestones are geologically categorized as either oolitic or dolomitic, and are commercially categorized as a building stone by density property according to ASTM C 568, Standard Specification for Limestone Dimension Stone.
Metamorphic
A change or alteration of solidified rock by heat, pressure, or intrusion of other minerals results in the metamorphic category, which includes marble, slate, and quartzite.
Marble is a metamorphic stone (originally a limestone) with a primary mineral composition of calcite and dolomite. It has sufficient hardness that it can take a polish finish. Commercially, there are more than 8000 varieties of marble, based on mineral content, colour, and geographic origin.
Marble dimension stone
According to ASTM C503, Standard Specification for Marble Dimension Stone, there are several classifications of marble building stone, but only a few are suitable for exterior cladding. Low-density Category l (12 per cent absorption) and Medium-density Category II (7.5 per cent absorption) are not for exterior use. High-density Category III (three per cent absorption) is only suitable for exteriors with supporting documentation. High-density stones such as Class I−Calcite or Class II−Dolomite are the best suited for exterior cladding and commercial flooring installations.
Class IV−Travertine is a form of limestone that often forms near hot, bubbly, mineral-rich springs. Gas bubbles become trapped and create a pitted surface on the stone. These pitted surfaces can be filled with an epoxy or dust resin. Filling the small holes and pits gives the travertine a more finished look.
The percentage of magnesium carbonate in marble generally determines its strength, colour, texture, and variety. Calcite marbles have 40 per cent magnesium carbonate. Travertine is geologically a limestone, and serpentine (i.e. Class III) is geologically an igneous stone—but as both are capable of taking a polish, they are commercially classified as ‘marble.’
Further, stone industry organizations classify marble into four fabrication, handling, and
working qualities:
- Group A: sound stone with uniform characteristics and favourable working qualities;
- Group B: stone similar to group A; may have some natural faults;
- Group C: stone with variations in working qualities, containing geological flaws, voids, and veins; and
- Group D: contains many of the most highly coloured, veined, and decorative marbles with substantial natural cleavage faults.
While fabrication classifications are not necessarily an indication of the physical properties or durability of stone, it is generally recommended only Group A and Group B marble are suitable for use as external cladding. For more information, design professionals should seek ASTM C1527/C1527M-11, Standard Specification for Travertine Dimension Stone.
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I like that you mention that stone cladding a good option to keep away frost or water absorption. It’s good for any building to be able to stand against the elements, whether that is cold or hot weather. I just moved to a new home in an area that rains a lot, and I have been considering doing stone cladding in order to help keep water away.