Stone like any other building material has its strengths and limitations, and these qualities are based upon the stones inherent properties.
During the selection process for a specific application if these natural properties are not taken into consideration or are not fully understood problems are more likely to occur. “Proper, function-oriented specifications” plays an important part as to whether a stone will be durable i.e. the ability to endure and maintain its essential and distinctive characteristics…resistance to decay, strength and appearance. If a stone is selected for a shower, say a nice Negro Marquina, a black marble or a Breccia marble based on their aesthetic appeal and their sensitive to moisture is not known or fully understood then stone failure is inevitable, spalling and vein deterioration. These stones can be said not to be durable for this particular application. Both these stones could be considered durable for medium to light traffic use in a residential setting. Durability becomes a relative issue. A particular stone will not maintain its integrity in one environment as illustrated with the Negro Marquina and Breccia, yet be considered a durable stone in another sitting.
Durability…is based upon the stones natural physical properties, characteristics
and the environmental conditions to which it will be or is subjected too.
The environmental conditions vary with exterior or interior, vertical and horizontal applications. Climatic conditions ranging from a freeze/thaw climate, a dry hot desert environment and coastal exposure. Wet conditions such as around pools/spas and in bathrooms (showers). High traffic pedestrian areas, etc.
Another factor of stones durability is its Aesthetic Durability or Dimensional Stability. Cosmetic changes may occur. This has to do with the Color Stability of certain stones. These changes can take place in two ways.
SUNLIGHT : When some stones are used in exterior applications and exposed to direct sunlight they fade or change color. Dark colored stones and those that contain organic matter will generally fade to a much lighter color. A personal experience I encountered involving color stability involved an interior/exterior installation of a crimson colored Coralstone. The exterior corelstone in the direct sunlight had faded 2 to 3 shades lighter in color. The interior stone had not experienced any color change. The corelstone being of a biogenic origin contained organic material that was affected by ultraviolet exposure.
MOISTURE : Some stones have moisture sensitive mineral contents that will cause the stone to develop rust spots, or other color variations, or contain moisture sensitive substances that will cause blotchy and streaking discolorations. Certain limestone’s contain bituminous materials that are soluble when exposed to moisture. Some marbles are also moisture sensitive when in high moisture areas, showers and those with steam features, these stones have a tendency to develop dark botches.
It needs to be emphasized…that because a particular stone will not perform well when subjected to certain environmental conditions, that this means the stone is of poor quality. Almost all of the problems that occur with stone are because the particular type of stone was not selected correctly for the use for which it was intended.
QUALITY
The issue of quality needs to be addressed and clarified regarding its relation to stone.
Quality and durability are often used interchangeably when dealing with stone problems. In defining quality it should be understood what quality standards are, and are not; in order to understand these standards, we need to know about stones qualities. Generally speaking, stone qualities can be classified into two categories…
INNATE QUALITIES : The physical properties and natural characteristics of stone.
The most important single factor in specifying stone is a thorough knowledge of the specific properties of the stone under consideration. The American Society for Testing & Materials (ASTM) has develop standard test methods for evaluating these properties. These tests are all definable and controllable. The results of the testing can be used to define the durability of the stone for a specific application. If a stone dose not comply with the standard guidelines for the intended application it in no way implies that the physical properties and natural characteristics of the stone are of poor quality. The ASTM standards are intended as guidelines to what should be used as a minimum for a specific application. The ASTM standards are not a classification system implying good to poor quality.
MAN-MADE QUALITY : Are those resulting from the fabrication process at the factory level…size, thickness, squareness, flatness and surface finish to name a few.
These man-made qualities can be objectively evaluated in relation to established industry standards. For instance, squareness…Squareness is determined by the four angles of the tile. If any of the four angles deviates from 90 degrees (a right angle) it will affect the other three angles. If the tiles are not square, the joints and seams in an installation cannot be aligned.
Quality can be applied to stone and measured against definable industry standards when it is pertaining to the fabrication process at the factory level.
The Marble Institute of America (MIA) has also assigned group classification to marble and stone for soundness of fabricating qualities. The classifications indicate what method of fabrication is necessary.
Group A : Marbles and stones with uniform and favorable fabricating qualities.
Group B : Marbles and stones similar in character to the preceding group, but with working qualities somewhat less favorable. These may have natural faults or voids. A limited amount of filling with color-blended materials are necessary.
Group C : Marbles and stones with variations in fabricating qualities. Voids, veining variations and lines of separation are common. Filling is necessary, and the use of reinforcements are employed when needed.
Group D : Marbles and stones similar to the preceding group, containing a larger proportion of the same natural characteristics and a maximum variation in fabrication qualities, requiring more of the same methods of finishing.
The issue of Quality could be referred to in the…selling…fabricating, installation and the knowledge of the stone during the…selection process and…not to the inherent properties of the stone its self.
The majority of the problems stone care professionals get involved with could have been avoided during the selection process.