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Polished concrete is a multi-step process where a concrete floor is mechanically ground, honed and polished with bonded abrasives in order to achieve a desired level of sheen or gloss.
The Concrete Polishing Process
Concrete polishing begins with floor preparation. During this process, the floor is inspected and cleared to remove all unnecessary materials that can damage both the floor and the grinding machines. Floor inspection also includes hardness testing. Before a floor can be polished, it must have a hardness reading of 4,000 psi or higher for best results. [1] A reading below this measure means the floor is soft and can crack under pressure. The next step is the initial grinding. In this step, low grit diamonds (e.g. 16- to 20-grit) are used to grind down all uneven surface until the floor is flat. [2]
The next step is patching. Normally, all concrete floors have cracks. Patching ensures that all cracks, pinholes, and micropits are covered with grout before the concrete polishing process continues. After patching comes floor hardening. This step is also called densifying. Densifiers make the concrete surface hard enough for grinding and polishing. Densifiers to achieve a minimum of 32 to 40 mpa (megapascal) before it can undergo grinding. [3] Densifying solutions also seal the floor from problems like rebar expansion, mildew, and mold.
Once the floor is hard enough, the next step is honing. This process is needed to refine the hardened surface using finer abrasives (e.g. 200- to 400-grit resin). After honing, the next step is polishing. Here, the floor is polished with much finer grit in order to achieve the desired sheen level, such as matte, satin, semi-gloss, and high-gloss. In a matte finish, the objects reflected on the floor have a hazy appearance. In a satin finish, the reflection of objects have a low-luster appearance. A semi-gloss sheen would have easily-identifiable reflections. Side and overhead lighting will also be visible. A high-gloss sheen will have highly identifiable reflections of images. When viewed from different angles, the floor will appear to be wet. [4]
Polished Concrete Densifiers
A concrete densifier is a solution used to penetrate into the concrete and create a chemical reaction to harden and dust-proof the surface. During concrete polishing, the surface is processed through a series of steps (in general a minimum of four grinding steps of processing is considered polished concrete) utilizing progressively finer grits of industrial diamonds bonded in metal, hybrid or resin to make diamond polishing pads.
Under certain circumstances polished concrete may be LEED approved. [5]
Concrete is not considered polished before 1600 grit, and it is normally finished to either the 1600 or 3000+ grit level. Dyes designed for concrete polishing are often applied to add color to polished concrete as well as other options such as scoring, creating radial lines, grids, bands, borders, and other designs. Any grinding under 1600 grit is considered a honed floor.
Polished lime mortar was discovered in the city of Jericho, in the valley of the River Jordan. According to the Bible, Jericho fell in 1200 BC. Researchers have since discovered several layers of concrete from earlier settlements. Among the layers was a polished screed floor. [6]
In 1886 and 1887, the Israeli archaeologist Garfinkle and retired professor Malinowski from Gothenburg in Sweden, who specialized in concrete, took the concrete samples and analyzed them in a laboratory. They determined the concrete originated in 7000 BC.
Malinowski stated that the lower part of the floor consisted of lime concrete with a thickness between 6-8 cm. He also stated the concrete was beige brown and had a very fine polished surface.
In simple terms, the process of polishing concrete is similar to sanding wood. Heavy-duty polishing machines, for example concrete grinder, are used to gradually grind down surfaces to the desired degree of shine and smoothness. The closest equivalent example would be polished granite or marble.
The mix design of the concrete should be 3500 psi or higher. The concrete should be poured full depth to take advantage of the concrete's full structural strength, and also help to prevent cracks. The concrete should always be professionally finished with power trowels and cured with water for seven days. Polishing should not begin until the concrete is fully cured (generally 28 days). The concrete slab can contain decorative aggregates to create many different aesthetic appearances, see Terazzo . The aggregates are often sized 8 - 20 mm, but almost anything can be used. According to the Global Concrete Polishing Institute, a FF (floor flatness) level of 50 or greater is desired to facilitate the polishing process. During the finishing phase, any decorative aggregates such as seashells, glass chips or even metal car parts can be dropped into the surface of the concrete.
Retrofit floors can be done in different ways depending on the conditions of the concrete. If the existing concrete is in good condition the surface can be polished to just about any standard. If the existing floor slab is in poor condition, it can be cut, or ground and the natural aggregate can be featured as the "exposure level". If the existing surface is in very poor condition a topping slab with a minimum thickness of 50 mm (2 inches) can be added on top of the existing slab.
A diamond polished concrete floor is time-consuming. Six to twelve steps of grinding may be needed. The general rule is to start the initial grinding with a coarse 30/60-grit diamond and finish with a 1600- or 3000+ grit diamond, depending on the exposure level of aggregate and gloss level required. The polishing process begins with a 50-grit diamond resin pad instead of a metal segment. When using the resin pads the steps may be 100, then 200, 400, 800, 1600 and finally 3000+ grit. Throughout the process, a densifier is used to harden the concrete surface, which allows the concrete to be polished. A number of densifiers can be used; these consist of lithium, potassium or sodium silicates. In some cases, a fine grout is also used to fill in any holes, cracks or imperfections that were exposed from the initial coarse grinding step. The concrete can be also finished with a natural-look impregnating polish guard, which penetrates 2–5mm inside the pores of the concrete to prevent staining from oils and spills. It is breathable as opposed to a sealer that does not allow vapor transmission.
This system is not considered to be real polished concrete, as there is little physical refinement of the concrete slab. However, it does provide a similar look to polished concrete, so may be appropriate in some areas. Typically, this system is referred to as a "half polish" as generally the surface is only processed through three steps of grinding (half the processing steps of a true polished concrete floor). The surface is densified, so the advantages of the densifier are inherited, then a concrete sealer or a high buildup of a concrete guard is used to create a shine. The "shine" is topical and generally wears easily, requiring high maintenance and reapplication of the material. While there is some level of refinement to the surface, the topical (chemical spray or rolled on) solution will wear off and need to be replaced depending upon the level of floor traffic. Grouting and patching may be required to fill any voids, holes, cracks or imperfections.
This system is not considered to be polished concrete as there is very little physical refinement of the concrete slab. However, it does provide a similar look to polished concrete and may be appropriate in small spaces with little expected foot traffic or wear on the slab. While there may be some level of surface preparation this is a topical (chemical spray or rolled on) solution and will wear off and need to be replaced depending on floor traffic. Grouting and patching may be required to fill any voids, holes, cracks or imperfections. The surface is then cleaned and prepared for the application of either a gloss or matte surface coating or an impregnating enhancing sealer.
Process involved in polishing concrete:
Level | Name | DISTINCTNESS-OF-IMAGE (DOI) GLOSS | IMAGE CLARITY VALUE, % |
---|---|---|---|
1 | Flat (Ground) | Images of objects being reflected have a flat appearance | 0 - 9 |
2 | Satin (Honed) | Images of objects being reflected have a matte appearance. | 10 - 39 |
3 | Polished | Images of objects being reflected do not have a sharp and crisp appearance but can be easily identified. | 40 - 69 |
4 | Highly Polished | Images of objects being reflected have a sharp and crisp appearance as would be seen in a near-mirror like reflection. May require grouting. | 70 - 100 |
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Polished concrete may be considered a form of sustainable design flooring, if less material is used than in comparable types of flooring.[ citation needed ]
Polished concrete floors have the following advantages:
LEED 2009 standards contain guidelines for using polished concrete flooring to qualify for LEED credits.
Service life depends on the surface quality and the usage. If the usage is heavy, the polished concrete floor will degrade. Cementitous concrete is not acid-resistant.
Even though polished concrete doesn't peel off like Epoxy and PU floors, damage may happen:
Lapidary is the practice of shaping stone, minerals, or gemstones into decorative items such as cabochons, engraved gems, and faceted designs. A person who practices lapidary is known as a lapidarist. A lapidarist uses the lapidary techniques of cutting, grinding, and polishing. Hardstone carving requires specialized carving techniques.
Varnish is a clear transparent hard protective coating or film. It is not to be confused with wood stain. It usually has a yellowish shade due to the manufacturing process and materials used, but it may also be pigmented as desired. It is sold commercially in various shades.
Terrazzo is a composite material, poured in place or precast, which is used for floor and wall treatments. It consists of chips of marble, quartz, granite, glass, or other suitable material, poured with a cementitious binder, polymeric, or a combination of both. Metal strips often divide sections, or changes in color or material in a pattern. Additional chips may be sprinkled atop the mix before it sets. After it is cured it is ground and polished smooth or otherwise finished to produce a uniformly textured surface. "Terrazzo" is also often used to describe any pattern similar to the original terrazzo floors. Modern forms of terrazzo include polished concrete.
An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflective surface, the process can also involve roughening as in satin, matte or beaded finishes. In short, the ceramics which are used to cut, grind and polish other softer materials are known as abrasives.
Tumble finishing, also known as tumbling or rumbling, is a technique for smoothing and polishing a rough surface on relatively small parts. In the field of metalworking, a similar process called barreling, or barrel finishing, works upon the same principles.
Grinding wheels are wheels that contain abrasive compounds for grinding and abrasive machining operations. Such wheels are also used in grinding machines.
Sharpening stones, or whetstones, are used to sharpen the edges of steel tools such as knives through grinding and honing.
Wood finishing refers to the process of refining or protecting a wooden surface, especially in the production of furniture where typically it represents between 5 and 30% of manufacturing costs.
Surface finishing is a broad range of industrial processes that alter the surface of a manufactured item to achieve a certain property. Finishing processes may be employed to: improve appearance, adhesion or wettability, solderability, corrosion resistance, tarnish resistance, chemical resistance, wear resistance, hardness, modify electrical conductivity, remove burrs and other surface flaws, and control the surface friction. In limited cases some of these techniques can be used to restore original dimensions to salvage or repair an item. An unfinished surface is often called mill finish.
Engineered stone is a composite material made of crushed stone bound together by an adhesive to create a solid surface. The adhesive is most commonly polymer resin, with some newer versions using cement mix. This category includes engineered quartz (SiO2), polymer concrete and engineered marble stone. The application of these products depends on the original stone used. For engineered marbles the most common application is indoor flooring and walls, while the quartz based product is used primarily for kitchen countertops as an alternative to laminate or granite. Related materials include geopolymers and cast stone. Unlike terrazzo, the material is factory made in either blocks or slabs, cut and polished by fabricators, and assembled at the worksite.
A diamond tool is a cutting tool with diamond grains fixed on the functional parts of the tool via a bonding material or another method. As diamond is a superhard material, diamond tools have many advantages as compared with tools made with common abrasives such as corundum and silicon carbide.
A diamond blade is a saw blade which has diamonds fixed on its edge for cutting hard or abrasive materials. There are many types of diamond blade, and they have many uses, including cutting stone, concrete, asphalt, bricks, coal balls, glass, and ceramics in the construction industry; cutting semiconductor materials in the semiconductor industry; and cutting gemstones, including diamonds, in the gem industry.
Decorative concrete is the use of concrete as not simply a utilitarian medium for construction but as an aesthetic enhancement to a structure, while still serving its function as an integral part of the building itself such as floors, walls, driveways, and patios.
Artificial stone is a name for various synthetic stone products produced from the 18th century onward. Uses include statuary, architectural details, fencing and rails, building construction, civil engineering work, and industrial applications such as grindstones.
Ceramography is the art and science of preparation, examination and evaluation of ceramic microstructures. Ceramography can be thought of as the metallography of ceramics. The microstructure is the structure level of approximately 0.1 to 100 μm, between the minimum wavelength of visible light and the resolution limit of the naked eye. The microstructure includes most grains, secondary phases, grain boundaries, pores, micro-cracks and hardness microindentations. Most bulk mechanical, optical, thermal, electrical and magnetic properties are significantly affected by the microstructure. The fabrication method and process conditions are generally indicated by the microstructure. The root cause of many ceramic failures is evident in the microstructure. Ceramography is part of the broader field of materialography, which includes all the microscopic techniques of material analysis, such as metallography, petrography and plastography. Ceramography is usually reserved for high-performance ceramics for industrial applications, such as 85–99.9% alumina (Al2O3) in Fig. 1, zirconia (ZrO2), silicon carbide (SiC), silicon nitride (Si3N4), and ceramic-matrix composites. It is seldom used on whiteware ceramics such as sanitaryware, wall tiles and dishware.
Abrasive machining is a machining process where material is removed from a workpiece using a multitude of small abrasive particles. Common examples include grinding, honing, and polishing. Abrasive processes are usually expensive, but capable of tighter tolerances and better surface finish than other machining processes
A concrete grinder is an abrasive machine for grinding and polishing concrete and natural stone. Concrete grinders can come in many configurations, the most common being a hand-held general purpose angle grinder, but it may be a specialized tool for countertops or floors. Angle grinders are small and mobile, and allow one to work on harder to reach areas and perform more precise work.
Concrete pavement restoration (CPR) together with concrete pavement preservation (CPP) is a group of various techniques used to maintain concrete roadways.
A diamond grinding cup wheel is a metal-bonded diamond tool with diamond segments welded or cold-pressed on a steel wheel body, which usually looks like a cup. Diamond grinding cup wheels are usually mounted on concrete grinders to grind abrasive building materials like concrete, granite and marble.
Diamond grinding is a pavement preservation technique that corrects a variety of surface imperfections on both concrete and asphalt concrete pavements. Most often utilized on concrete pavement, diamond grinding is typically performed in conjunction with other concrete pavement preservation (CPP) techniques such as road slab stabilization, full- and partial-depth repair, dowel bar retrofit, cross stitching longitudinal cracks or joints and joint and crack resealing. Diamond grinding restores rideability by removing surface irregularities caused during construction or through repeated traffic loading over time. The immediate effect of diamond grinding is a significant improvement in the smoothness of a pavement. Another important effect of diamond grinding is the considerable increase in surface macrotexture and consequent improvement in skid resistance, noise reduction and safety.
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