The use of natural stone in architecture by humans was initially associated with a subconscious appreciation of its invulnerability, durability (strong as a rock). With the development of art, the color and pattern of the stone began to take center stage in its use. In terms of strength characteristics and durability, it is unlikely that any other building material can compare to natural stone. Wood and plastics deteriorate over time, iron inevitably rusts, and only natural stone can stand in a structure for thousands of years. And yet, not all stones are the same, so when using it, certain specific rules must be followed to ensure that the time and money spent are not wasted. Let’s determine, without delving too deeply into specialized scientific knowledge, what needs to be considered when choosing natural stone for stone cladding.
🔍The color and pattern of the stone
As a rule, after the decision is made to use natural stone for cladding, the future owner or their representative, together with the architect, selects the stone according to their taste based on its color and pattern. In nature, there is a wide range of color shades of stone, but it should be noted that such saturated colors as blue, purple, and yellow are quite rare, and the cost of products made from such stone can increase several times compared to stone of ordinary color shades. Moreover, the most saturated and bright varieties of stone will also inevitably have a high cost.
Products made from artificial materials can be manufactured with predetermined properties. Natural stone, on the other hand, was formed by Nature. The variability of the properties of natural stone depends on the conditions of its formation. Such conditions have changed repeatedly over millions of years, leading to variability in the properties of the stone. This must be taken into account when selecting material for stone cladding. In the case of Jurassic limestone, which, being a sedimentary rock, was formed 135 million years ago, it is found in large layered masses. Over more than 150 years of industrial development of Jurassic marble quarries, literally every layer has been studied, which allows us to guarantee its visual characteristics with a very high degree of certainty.
The most stable in terms of preserving color shades and patterns are gabbro and labradorites. Some granites are capable of maintaining their decorative properties over a significant period. The most variable in terms of color and pattern are marbles and gneisses. Here, it is very difficult to find a matching pattern for two adjacent slabs. In such cases, an experienced supplier of cladding materials conducts a computer layout of the blanks (slabs) and coordinates this layout with the Customer. If you have a responsible project with increased design requirements, such a layout must be carried out. This approach, of course, is not limited to the types of stone mentioned above; the selection of Jurassic limestone from a reputable manufacturer always begins at the quarry.
Based on the selected and agreed small samples of Jurassic stone for a specific project, slabs of this stone are chosen, photographed, and recorded directly at the quarry in the presence of the architect and the client, with the quarry and layer clearly documented. All unacceptable visual defects and maximum deviations in shade and appearance are marked on the representative slabs. It should also be noted that the moisture content of fresh slabs is higher than that of the sample, so for a full comparison, the surface of the Jurassic stone should be dried, for example, with a gas torch flame. The illustration shows the difference between the selected small sample and the dried/raw slab of the same layer.
🔍Sometimes, when it comes to flooring, ready-made format slabs of the chosen layer are displayed side by side to select suitable options for the shade and saturation of the fossils.
🔍Strength properties of stone
As a rule, the Client pays little attention to the physical and mechanical properties of the stone, and when combined with the limited information about the stone available to the Project architect, this often leads to undesirable consequences.
It should be noted that the stone, depending on the area of use, must have certain properties. For floors, for example, slabs made of certain types of limestone, slate, Roman travertine, and shell rock cannot be used due to their high porosity and weak abrasion resistance. Naturally, stone with increased radioactivity cannot be used indoors. Bases cannot be faced with stone that has water absorption of more than 0.2% without special measures to prevent it from getting wet. For exterior cladding, it is possible to use stone with frost resistance of at least 50 F (the stone withstands 50 cycles of alternating freezing and thawing without significant loss of strength). In large cities with heavy traffic and possible use of salt reagents, stone with frost resistance of at least 150 cycles must be used. For ventilated facades, the use of natural stones of high and medium strength is permitted. Low-strength stones with a compressive strength of less than 50 MPa (500 kg/cm2) are prohibited from being used in ventilated facades.
To determine whether a stone is suitable for cladding or not, it is necessary to assess its physical-mechanical and chemical properties. In external cladding, the stone is subjected to temperature fluctuations, atmospheric precipitation, salts, acids, freezing during the winter period, and can therefore be damaged.
🔍Destruction of stone during its frost weathering
Therefore, the requirements for stone in external cladding are more stringent, while for internal cladding they are less so. Such requirements are outlined in GOST 9479 - 2011 "Blocks made of rocks for the production of facing, architectural, construction, memorial, and other products. Technical specifications."
Requirements for natural stone for exterior cladding
To conduct a complete set of physical and mechanical tests, at least 40 correct cubes measuring 50×50×50 mm, 4 plates measuring 200×200×30 mm (to determine resistance to impact), and 3 polished texture plates measuring 300×300 mm (to determine mineralogical-petrographic characteristics) are required. The stone cubes for laboratory tests must be of correct shape. Non-parallelism of the faces can lead to significant distortions in the test results.
🔍Cubes and slabs of natural stone received for laboratory testing
Research on the technical properties of stone in the testing laboratory is conducted according to GOST 30629-2011 "Materials and products for cladding made of rocks. Testing methods." As a rule, laboratory tests should accompany each new batch of cladding products. The properties of the stone should be reflected in the technical passport attached to the batch of stone. It is worth noting that one of the main physical characteristics of stone affecting its durability is its frost resistance. This ability of the stone to resist destruction from alternating freezing and thawing during late autumn and early spring is characterized by its frost resistance. The importance of this material characteristic in our climate in large cities is also determined by the fact that water with dissolved salt (in our case, a mixture of anti-icing agents) exerts greater internal pressure on the capillary structure of the stone when it freezes, leading to even greater destruction of facades. But we will discuss this separately a little later.