Crystallization zones in granite cause weakness and warping.
Granite is the most common igneous rock occurring on the earth’s surface. Although it is a strong, durable material for building and decoration, granite can warp. A 3/4-inch slab can appear to have bent by 1/4 inch. An increase in thickness appears as a dome or “belly” within the slab or tile. This deformation is the culmination of a series of processes that start from molten granite rock itself and compound through quarrying, cutting and the installation of a slab or tile in a building. Does this Spark an idea?
Granite intrudes into the earth’s crust as a molten, plastic-like magma. As it cools and crystallizes in places, tectonic forces deform the granite and cause a temperature increase that re-melts the rock. A continuing process of crystallization, re-melting and re-crystallization over geological time produces swirls and stratification of different crystals in granite that make it an attractive decorative material. The same stratification forms zones of weakness within the granite which become apparent after mining.
The main components of granite are a gray quartz, pinkish feldspar, black mica and blue or green hornblende. The best quality granite, black granite, is one with the least proportion of quartz and a fine, uniform crystalline structure. As granite cools in the earth, quartz can crystallize into veins that create zones of weaknesses. Quartz also cools into glass in the granite and devitrifies over time. These zones can deform in the slab during its polishing and look like warping.
The cheapest method of granite extraction is by drilling holes into a mass of rock in a quarry, loading the holes with dynamite or other explosive and blasting the rock face. This procedure introduces minor cracks throughout the mined granite. The cracks warp the rock slab or laminate over time. The best, and most expensive, way to mine granite free of defects is to use stone cutting tools that do not leave cracks.
The feldspar content in granite makes it susceptible to moisture attack. Feldspar reacts with water to form clay such as kaolinite, or China clay. A common problem with granite tiles and countertops is moisture seepage through any unpolished underside or the granite unit, usually via an ineffective seal between the wall, floor or furniture. If these chemical reactions occur along pre-existing lines of weakness such as cracks, they are sufficient to warp granite in the same way as timber warps.
The adhesive used to bond a granite slab, tile or laminate to a surface must be one that sets hard and remains inflexible. Epoxy, a combination of a resin and a hardener, is recommended for attaching granite and other natural stone to a surface. Other adhesives may fail and allow moisture into the seal and cause warping or the detachment of the whole granite surface.
Poor cutting, laminating and polishing produce defects such as warping in every material. Top quality workmanship on a granite slab or tile can never compensate for defects in the original material such as cracks, moisture damage and quartz crystallization zones. Any attempt to compensate for poor quality granite by clamping, wedging in place or increasing the thickness of an adhesive usually compounds the warping effects.