Granite is a rock that has been formed over many millions of years. Granite consists of quartz, feldspar and mica; hence it is composed of minerals and metals. No two pieces of granite are the same, which makes each piece of granite unique in appearance. It owes its distinguishing features to the effects of nature, which gives each piece of granite a “personality” and charm and reveals its long life.
Slate (Basic Line)
Slate is a relatively soft, layered rock formed under pressure, which varies in thickness. Slate consists of compressed layers of clay, minerals and materials from over-lying layers that easily split from the layer where decomposed rocks or shellfish are deposited in water. There are several kinds of slate, e.g. clay, quartzite and mica slate, and these appear in different shades of colour, such as black, green, blue, white and red. Naturally cleaved slate plates are never of the same thickness when separated. Slate does not tolerate any form of acid treatment.
Basalt (Mountain Black)
Basalt is colloquially referred to as granite, but it is actually formed by volcanic activity and is not composed in the same way as granite. Basalt contains iron and magnesium silicates. Basalt is very ferruginous and hence does not tolerate any form of acid. Acid discolours basalt.
Travertine is a natural stone like marble, granite, onyx, limestone, slate, etc. The most important differences between travertine and other natural stones are its rock formation, and the stone's hardness and appearance. Travertine is formed in heat sources and/or limestone cavities. Travertine is not the same as marble or limestone, which come under the category of metamorphic rock. An important feature of travertine are the cavities in the stone, which are caused by the removal of carbon dioxide.
We have described and explained below the natural appearance/features of the different types of stones, which should be borne in mind when choosing the type of stone as these must not be confused with defects that may give cause for complaint.
Natural stone with these natural designs can vary a lot, as differences in colour may appear on the same element. Some natural stones may give the effect that certain areas lack the original background colour. On other types there may be large grain markings which are suddenly broken by a transverse grain, or thin streaks that may resemble splits. These elements may be appreciated by those who like purely natural products. This is something the customer should bear in mind when buying natural stone. All stone types may have variations in colour or grain. These are most noticeable, however, in granite.
Natural staining dark/light.
This is most often encountered on fine-grained types of granite. Natural staining appears as dark or light stains of varying sizes. The stains can be of a single colour or consist of several colour variations. This staining cannot be avoided.
These are found in almost all types of natural stone. Cavities (Tarolli) are the deposits of a small animal or fungus that has decomposed or rotted away. Fissures represent the distance created by nature between the different stone types, when rock under pressure and very intense heat fuses together over millions of years.
These appear on all types of natural stone with a sanded surface. Grinding marks tend to be circular in the markings, as these marks are made by the sanding blocks during grinding. Grinding marks are unavoidable on polished stone, as the marks are made by the final sanding block before polishing.
The effect of deposits of large quantities of dead shellfish and other matter and the agglomeration of various organic materials accumulating in layers on the sea bed, combined with an immense water pressure, is that we now have a product that can be used as a building material in a variety of ways. The agglomerated product may have undergone displacements in the layers or even earthquakes, causing fissures in the mass through which water has seeped, creating a build-up of organic materials, for example, silica. These materials have fused with rest of the mass, becoming one homogeneous mass. Thousands of years ago part of the sea bed was forced up above the sea level, forming land masses with hills and valleys. Chains of mountains also came into being in this way. It has now become possible, through modern working methods, to “break” blocks of the agglomerated mass, which can be sawn to make, for example, window panels 2 or 3 cm thick or tiles 1 cm thick. The fissures mentioned previously now appear as grains in the slabs, known technically as “glass grains”. These grains do not in any way make the slabs weaker. The tensile strength is greater precisely at the point where the glass grains occur. Glass grains can be found in a lot of natural stones - in granite as well as slate. We hope that this summarised explanation of how natural stone may have originated has assured you that “natural defects”, with the proper professional treatment, do not give any grounds for complaint.
Miscolourings on natural stone surfaces ”Picture framing”.
Apart from organic components, many natural stones also contain other compounds, mainly iron compounds. The alkaline water that is used in certain types of adhesives and caulks dissolves these compounds and reacts with them. This compound is then forced up to the surface of the natural stones. Oxidation may then occur. This tends to be found on light granite types. We recommend the use of laying materials that are approved as natural stone at all times.
Minor rust stains may occur in natural stone. These are caused by ferrous particles which react and may result in the extraction of rust.
Natural wastage (6%)
As this is a natural product, we must accept that stones may be damaged one way or another. Natural stone often originates from far way, which also leads to a lot of handling. In our industry, up to 6 per cent wastage is accepted, which a customer must also accept. This applies in particular to large deliveries and we recommend that this should be included in the calculation. Discarded tiles are for example used by means of cutting up, etc
Tolerances of +/- 2 mm in relation to the stated targets will be accepted.