The surface finishes technique is performed to is carried out to give the stone material certain aspects that make the most of the expressive possibilities: texture, color, roughness, roughness and drawing.
Often these treatments also improve the material quality and modify some properties, such as a greater resistance to weathering or to absorption.
The selection of the adequate finishing to be applied to the material is determined mainly by two factors: the resulting color and of course the cost of such work.
The evolution of finishing processes is complex over time, historically impact treatments as Bush-hummering and trimming performed with appropriate tools, as chisels and drills of various kinds were used. Treatments for shim, as polishing obtained by using abrasive products were also used. Today's operations include a wider range of surface treatments such as:
- Treatments obtainable through natural and artificial disjunction of rock:
- Quarry floor surface;
- Surface to “gap”;
- Frame sawn surface;
- Block-cutter sawn surface;
- Diamond wire sawn surface;
- Treatments obtainable through machining impact (mechanical):
- Bush hummering;
- Treatments obtainable by thermal action:
- Treatments obtainable by mechanical actions by shim washer:
- Treatments obtainable by using chimical products:
Treatments obtainable through natural and artificial disjunction of rock:
Quarry floor surface, surface to “gap”: These two categories have many similarities, for this reason they are analyzed together. The rough natural surface, owned by the material, is kept unchanged in its features to the laying. The splitting operation, while causing the rupture of the material makes it possible to maintain the natural look. (Figure 1).
The material shows its natural structure when it is split by mechanical forced action or for the ease of cleavage that it presents. There are several natural methods to split and divide the stone material; some materials are already in slabs in the quarry (as Stone of Barge, Atesine Porphyry), others are compact enough to produce blocks through sawing frame or flaked by simple percussion (Ligurian slate, Cardoso stone), lastly some material of high compactness can produce block through frame sawing, but at the same time they can be flaked up to millimeters thickness (Gneiss, Luserna stone). The definition of "quarry floor surface" refers to all those materials that are already in slabs in the quarry and which the production of blocks is made impossible due to this feature, while the diction “surface to gap” refers to those material whose natural surface was induced to gap, more or less easy to produce, with various type of tools.
The quarry-plane surface are used to create elevation combined afterwards in various use situations; in the “granitoid” materials and in the quartzites this type of surface generally offers a slight roughness, an optimal resistance to the use and overall good mechanical properties. For these characteristics these materials are used mainly for external accommodation, as flooring. Instead for surface to gap, it is necessary make a distinction between manual and mechanical gap. The main difference is only in the use of machinery for the same type of processing, therefore almost identical materials are obtained from the point of view of the final result.
Frame sawn surface: This surface is obtained through multi blade frames. Depending on the abrasive product used during the processing (diamond or grits), different final aspects are obtained at the end of the process. The final product may have more or less regularity on the surface, depending on whether they are granite (for which special mechanical grits are used) or marble (for which diamond blades are used). In the granite process can occur some problems, such as flatness defects, scratches or grooves, because of the used technique, which can be overcome with subsequent shaving treatments (honing and e calibration). (Figure 2)
Block-cutter sawn surface: it is obtainable artificially applying diamond wheels on the block cutter machine and so the surface is semi-smooth. In this process, due to the high accuracy of diamond wheels, the imperfections due to irregularities, scratches etc. are kept to a minimum so the final appearance of the material (marble or travertine) turns out to be a good regularity and flatness. Block cutter machines are primarily used in situations where it can be tolerated a certain degree of deviation from extremely meticolous thicknesses and sizes, such as skirting boars, in some outdoor flooring or in elements used as a coating. (Figure 3)
Diamond wire sawn surface: it can be obtained by sawing through diamond wire machines. It is a high precision process (unthinkable until a few years ago) to obtain surfaces with very low irregularity, optimal as a basis for subsequent processing and material transformations. This technique can be used in all those situations where the material to obtain does not have to comply with strict tolerances, or in the many situations of building cover elements without any particular pretensions aesthetic level. (Figure 4)
Treatments obtainable through machining impact (mechanical):
The mechanical impact can be obtained through the use of percussion tools such as chisels, hammers, topping bits, pens, gradinas, erasers ecc.
The different types of processing, according to a large number of tools, can take different names, such as: trimming, rifling, bush hummering, pitting, chipping, rolling, scratch, chiselling; many of these names derive and are closely related to the type of processing and finishing process already in antiquity.
Bush-hammering: this type of processing is one of the oldest, it is mainly done to external elements and it gives the surface a special sculpted look, because at the end of the process the surface is rough and embossed. This type of processing is adaptable to any type of stone, although historically it was more used to the marbles. Bushhammering allows to work on the surface, also to reduce the slipperiness in those areas subject to foot traffic (steps). Nowadays Bush-hammering is also used to minimize the differences and chromatic variations, because in the processing phase it first acts on the colour and on the texture of the stone material. The Bush-hammering has evolved over time, replaced the manual hammer (hammer to dense pyramidal tips).The Bush-hammering of mechanical type can be divided into two types: manual or automatic. The mechanical-manual Bush-hummering works on the material surface with pneumatic tools that cover, using a manual shift, the entire surface of the stone. This solution is most suitable in cases where the element to work has complex shape and its size is not high. The auto mechanics Bush-hammering uses more complex instruments such as bridge sawing machines which are equipped with one or more hammers which, flowing along the surface (defined in this case "bridge") affect the surface of plates below. Nowadays there are also tools that operate a rotopercussion action, combining percussion with a rotary movement of the heads. A flaw of this type of work is that the edges are not easily workable, because it is impact machining that subjects the part being worked at high mechanical stresses that often can cause the breaking out of the edges. (Figure 5)
Spuntatura: it is the holdest processing manually done by skilled operator with chisel and mallet. It consists of a processing done by manual hammer chisels that determine the various product dimensions. On the surface there are depression areas that can be thin, medium or large, according to the final result to be obtained. A type of spuntatura is martellinatura that is one of the finishing operations which, historically, was applied on the blocks just mined in the quarry. It was used bush hammer with big or thin jags this enabled him to obtain the so-called anathyrosis (i.e. braid) for a perfect catch rocks with one another to conclude that with a good degree of finish, in laying. Fine-grained or medium fine-grained materials are more suitable for this type of finish surface(Figure 6)
Chiselling: this finish is suitable optimally for the raw products, shiny and smooth. It was historically created manually by using tools such as chisel and mallet forming etchings, from 8 to 15 mm width, more or less deep by 2 to 5 mm and spaced from a variable wheelbase by 15 mm to 8. This finish is made both wet and dry using a variety of tools such as, single or multiple ruling hammers. The end result of this process depends, for the most part, by the "sharpness" and the depth of the furrows and also uniformity that the material presents. Granites are particularly enhanced by this specific processing because it creates on the surface kind of Visual disruption of the plot consisting of intertwined crystals between them. (Figure 7)
Gradinatura: this is a variant of the chiselling. The main difference is the aesthetic result of the two processes; nella gradinatura vi è una superficie finale striata in maniera più fitta e irregolare rispetto alla rigatura. In “gradinatura” there is a final surface streaked in a more dense and irregular compared to the chiselling. The "gradina", hence the term “gradinatura”, is a cutting tool used in the past, which includes a 15-25 cm, round or octagonal section of the cutting part of the teeth of different sizes. To affect a specific stone surface with a certain predetermined angle are necessary from two to fourteen teeth. Nowadays the gradinatura is done using a tool shaped like a roller. (Figure 8)
Sandblasting: it consists in projecting in high speed and pressure, on the product to be processed, an abrasive mixture of air and sand. Once blasted the surface takes on a rough appearance but not sharp and often turns out to be smooth and free of major discontinuity. This process is very invasive, for the amount of abrasive material carried. Nowadays it is mainly used for cleaning the blackened stone surfaces and degraded over the years by the action of atmospheric agents. Blasting operations can be large scale or small scale. To have high productivity, machines, that are used, have similar structure of bush hummer machines and they have dual function of bush-hammering and sandblasting. Sandblasting is also used in funerary art and in those fields where it requires written on the surface of the stone. (Figure 9)
Treatments obtainable by thermal action:
Flaming: it is an area which is obtained after a treatments with flame at a very high temperature, produced by special instruments as blowpipes (single and multiple) that, through the oxygen used as combustive agent and propane and take as fuel, run over the material surface, which can reach temperatures of 2500° C. The surface, run over by the flame, is subjected to very high thermal shock and so it vetrifies, making a roughness and embossment specific of this treatment. This type of processing is specifically suitable for granites, because of their polimineralica composition, which provides excellent colour rendering, while the results are poor for other categories of stone material. For granites the end result is also optimal due to the different thermal expansion coefficients of various polimineralici aggregates, which contribute to an excellent final result. Thermal expansion caused by the flame, is differential and leads to lifters, disjunctions and secondments of crystals in different points of the surface. Unlike granites, marbles, which consist of a single material (calcium carbonate), do not have different coefficients of thermal expansion, for this reason, this type of treatment is not ideal. The machines used for flaming has the same operation typology of bush hummering machines, indeed very often a single machine performs both functions. The flaming is often used as a treatment for the stone materials used for outdoor use because this process increases the degree of weathering. (Figure 10)
Treatments obtainable through mechanical abrasion:
the treatments obtained by shim actions are performed using abrasive tools such as grinding wheels, plates, rollers, etc. Normally it refers to three major operations: calibrating, sanding and polishing. The succession of these workings presents different aspects depending on whether they apply to semis standardized type such as tiles or large slabs.
Calibration: the aim of this treatment is to make the material in process surface the more planar possible and to check the surface removing surpluses formed during the sawing process. Control of thickness and flatness of a product are extremely important for a correct installation and for the success of the next two stages of sanding and polishing. (Figure 11)
Honing and polishing: are two operations that allow to make the surface of the material being machined smooth and shiny. The polishing process differs depending on whether it is performed on a marble or granite. On the marble polishing takes place takes place by means of a chemical process using basic polishing of oxalic acid. The reduction of the water in the final phase of the abrasive treatment causes a heating of the material that forms a patina on the surface.
For granites polishing is essentially composed of a mechanical phenomenon by means of felt with lead oxide and Tin carrying the "closure" of the material by applying abrasives to progressively finer grit. Polishing is done to get a high degree of exaltation of the decorative and aesthetic quality of stone material. Translucency is a treatment which forms part of the polishing, it represents the transparency that allows to perceive the image of a given subject, without distinguish clearly the contour Translucency turns out to be an interesting application in construction, as natural stones, reduced to thin, cross easily from both natural and artificial light. This allows to create suggestive play of light in modern architecture and interiors to enhance certain areas with varied textures of material that are reflected on the walls. (Figure 12)
Treatments obtainable by using chimical products:
the treatments using chemical products meet many needs:
- strengthening and consolidating Actions;
- particular superficial aesthetic effect;
- increased resistance to meteoric agents.
Resining: is an operation that causes an increase of the resistance of the material reinforced by resins to give greater compactness. The resins used in this treatment are: epoxy resins, polyester resins. The practice of resining is done either on slabs on stone blocks, usually apply on both sides of the plate, depending on the material weakness showed. This processing is not suitable for granites, in exceptional cases, is used for stopping up small holes visible on the surface.
Grouting: in this operation, carried out typically on travertine, fractures and cavities are sealed by means of mastics and stuccos by appropriate tones to the colour of the material. Grouting operations can be manual (from putty spatulas) or automatic (grouting machines). Once resined and puttied, the stones are polished or honed one last time before being laid up in the final phase. The term “antiqued surface” is used surface with antique look obtained by a simulation of aging caused by time and wear. The materials most suited for this type of process are those who possess a limited medium-hardness such as marble, travertine or very compact breaches. It can be realized in the following way: the previously selected pieces, are placed in machines called tumblers, combined with water and mixed by rolling or other types of mechanical movement. (Figure 13)