(4) Polishing

The polishing process is an important process for the terrazzo effect. The main purpose of polishing is to grind off the cement slurry on the surface layer and smooth the stone ballast on the surface.

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There are two types of polishing: mechanical polishing and manual polishing. If the construction conditions permit, mechanical polishing should be used as much as possible, which not only works faster, but also reduces the labor intensity a lot. If a grinder is used for polishing, an abrasive tool is generally used. The structure of abrasive tools generally includes abrasive particles, binders, pores and fillers.

The abrasive grains are the main body of the abrasive tool, and the edges and corners exposed on the surface of the abrasive tool are used as cutting edges to cut the terrazzo. There are many kinds of abrasive materials, such as quartz sand, corundum, natural diamond, carbide and so on. According to different purposes, the abrasive is processed into particles of different diameters.

The binder is the bonding material of the abrasive tool, which acts to consolidate the abrasive particles, making it an abrasive tool with a certain shape and strength.

The pores are the voids inside the abrasive tool, which can exclude grinding and accommodate cooling water during grinding. Due to the large amount of chip removal in the rough grinding of terrazzo, if the abrasive tool is tightly organized and the place to accommodate the grinding chips and cooling water is small, it is not only possible to burn the plate, but also affect the gloss of the plate surface. Therefore, in order to overcome this phenomenon, a part of soft materials, such as aerated concrete or perlite particles, are generally added inside the structure of the abrasive tool.

Polishing mainly controls two points, one is to control the grinding time ; the other is to master the number of polishing times. If the grinding time is not well controlled, it will affect the work efficiency and quality. If the grinding is started early, the strength of the cement ballast slurry is too low, which will cause the ballast to loosen or even fall off. If the grinding time is late, the strength of the cement ballast slurry is high, which will bring difficulties to the grinding. To achieve the same effect, it will take a correspondingly longer time.

Different cement grades, different proportions, and different temperatures all have an impact on the hardening and strength of cement ballast slurry. In order to obtain a suitable grinding time, the best way is to determine it after trial grinding.

The number of times of polishing is different for different grades of terrazzo floors. Ordinary terrazzo made now generally needs to go through no less than "two pulping and three grinding" to achieve the desired effect. For advanced art terrazzo, the number of polishing times should be appropriately increased and the fineness of the whetstone should be increased. Under normal circumstances, the first grinding should use a coarser grinding wheel, usually 60 to 80. This time, it is required to be smoothed and evenly ground, so that all the stones and grids can be clearly exposed. After the first polishing is completed, drain the turbid slurry, rinse the surface with clean water, and then check the surface flatness with a ruler. The first pass has a certain degree of wear marks on the surface due to the coarse grinding wheel. In addition, grinding away a layer of the grout exposes surface defects, such as blisters, small holes, and air bubbles. These surface defects should be rubbed with grout of the same color on the same surface, commonly known as grout. After 2 to 3 days of maintenance, the second polishing can be carried out.

For the second polishing, use a finer grinding wheel than the first, and the grinding method is the same as the first. This time, it is required to remove the wear marks and polish the surface. For local pockmarks and small defects, repair them with the same color cement slurry. After 2 to 3 days of curing, the third time can be polished.

For the third pass, use 180-240 fine grinding stones. This time, the surface should be smooth and flat, without blisters, no pores, and the stones are evenly exposed. Due to the poor mechanical control of the corners, it should be properly ground by hand, and finally rinsed with water.

(5) Waxing

The purpose of waxing is to make the terrazzo floor brighter, smoother and more beautiful. It is also easy to maintain and clean due to a thin layer of wax on the surface. Waxing starts after the top coat is completely dry. Before waxing, in order to make the wax liquid better bond with the surface layer, the surface layer should be scrubbed with oxalic acid. The function of rubbing oxalic acid is mainly to clean the residual cement slurry and fine stone powder on the surface layer, so that a small amount of suspended slurry and powder material deposited on the surface can be eliminated by the action of oxalic acid. Oxalic acid, chemical formula (COOH)2, is the simplest dicarboxylic acid, which is a kind of colorless crystal, easy to soluble in water. Oxalic acid is prone to chemical reaction with calcium hydroxide in cement, and has weak corrosion and surface decontamination effects on the surface layer. Therefore, scrubbing with oxalic acid before waxing can ensure the bonding between the wax liquid and the surface layer and improve the effect of finding wax.

When oxalic acid is used, first dissolve it into a 10% oxalic acid solution with water, sprinkle it evenly on the surface layer, then lightly grind it with a whetstone, and then rinse it off with water. After the ground is dry, it can be waxed.

Waxing, also known as wiping wax, generally uses floor wax, which is a wax product for protecting and decorating the floor. It is composed of natural wax or solid paraffin extracted from petroleum and solvent.

Waxing commonly used the following two methods. One is to use cotton yarn (or thin cloth) dipped in the finished wax to rub a layer on the surface. After drying, use a grindstone machine to tie a sack (or hemp) roll, and rub it several times until it is smooth and shiny. Another method of waxing is to apply the finished wax on the surface layer, bake it with a blowtorch, make the molten wax penetrate into the pores, and then polish it.

The ground that has been waxed should be bright and smooth, the surface is smooth and delicate, the stones are clear and beautiful, and the color is uniform. If there is dust accumulated locally, it can be gently wiped off with a mop dipped in a small amount of kerosene.