In northern rural areas, scraping white is still used. The main raw material for scraping white is Shuangfei powder, also known as "white powder". Its main ingredient is heavy calcium carbonate, which is also referred to as "heavy calcium". It is usually used to fill walls and ceilings, cover them, level them, scrape them flat and brush them white.
In urban home decoration, putty is commonly used as a wall substrate and leveling. The main components of putty are used in combination with gypsum powder, talc powder, white cement, and binder. Gypsum powder can accelerate the drying period. White cement plays a bonding role. Talc powder makes the wall base smooth and delicate. In building decoration, putty is divided into paste putty, dry powder putty, and two-component putty according to its shape.
According to the standard classification of JG/T3049-1998 "Putty for Interior Construction", interior wall putty is divided into Y type and N type, Y type is general type, N type water-resistant type, and putty with certain water resistance. Y-type putty is commonly known as ordinary putty, 821 putty, etc. At present, such putty on the market is basically a low-cost and inferior building decoration material produced by pre-gelatinized starch, carboxymethyl cellulose mixed with double fly powder, talc powder and other raw materials. Because the cementing material used itself has degradable properties, the coating is easy to pulverize, and mildew and degrade quickly in case of moisture, which is easy to cause coating pulverization, cracking, hollowing, and falling off. At present, the interior wall putty produced in the vast areas of our country is still generally made of polyvinyl alcohol 107 glue, carboxymethyl cellulose mixed with double fly powder, talc powder and other powder materials. Although the cost is lower than that of imported rubber powder and emulsion mixed powder materials, there are still complicated processes and high costs. In particular, it contains a large number of harmful substances such as formaldehyde, which can cause damage to the human nervous system, and can cause poisoning and cancer in severe cases, especially to infants and young children and the elderly and infirm.
Water-resistant putty is usually made of lime calcium powder, talc powder, etc. as the main raw materials, and is composed of hydroxypropyl methyl cellulose ether (HPMC), polyvinyl alcohol powder, redispersible latex powder and other raw materials. Calcium ash powder is a powdery substance with a white appearance, mainly composed of CaO, Ca (OH) 2, CaO and water form Ca (OH) 2, Ca (OH) 2 reacts with CO2 in the air to form hard CaCO3, so that the coating has good water resistance. The water-resistant putty is white and delicate, and feels good. It has a porcelain-like effect (need to add a calendering process). It has good water resistance and does not hollow or fall off after soaking in water for 7 days.
It is called imitation porcelain paint in the Central Plains, but it is actually a water-resistant putty. After the calendering and polishing process, the surface of the putty forms a rather smooth effect.
After the polyvinyl alcohol powder is dry mixed with other powders, water is added to form a paste-like slurry. After the water evaporates, a frame structure composed of inorganic and organic binders is formed, that is, a brittle and rigid skeleton composed of hydraulic materials, and the flexible connection of the film-forming structure between the gap and the solid surface of the polyvinyl alcohol powder. This connection can be imagined as being connected to a rigid skeleton by many small springs. Since the tensile strength of the polymer resin film formed by polyvinyl alcohol is much higher than that of the hydraulic material, the strength of the putty itself is enhanced, that is, the cohesion is improved. Due to the flexibility of the polymer, the deformation ability is much higher than that of the rigid structure formed by hydraulic materials, etc., which can improve the deformation ability of the putty, and the effect of dispersing stress is greatly improved, thereby improving the crack resistance of the putty. The water resistance of polyvinyl alcohol powder is weaker than that of redispersible latex powder, but in the alkaline system of water-resistant putty containing cement, polyvinyl alcohol will be saponified by the alkali generated by the hydration of cement in the putty, and at the same time absorbed by quartz-like materials, the hydrophilicity of polyvinyl alcohol is greatly weakened, so it will not affect the water resistance of the water-resistant putty.
The strength of exterior wall putty depends in part on the strength of the cement itself. Cement is a hydraulic material and requires an appropriate amount of water maintenance to achieve strength. Because the coating of the putty itself is relatively thin, if the moisture maintenance of the putty itself is not enough, it may cause the putty to lack water and cause pulverization and powder removal. You can appropriately increase the amount of cellulose ether, or adjust the amount of polyvinyl alcohol powder.
Part of the strength of the thin layer putty comes from organic binders. Generally, adding 3-5 kg of polyvinyl alcohol powder should not drop the powder.
Sometimes the finished putty produced will experience de-powdering and rough feel, which is mainly due to the widespread problem of impure fillers. To check the quality of ash calcium and cement in the filler, in Beijing, Tianjin, Shanxi, Shandong, Henan, and Shenyang markets, the ash calcium contains more than 60-70% white powder, the cement contains more than 60% white powder, or the construction does not master the calendering time, and the control of putty 80% dry is the best time for calendering, which is easy to cause de-powdering phenomenon. The appearance of non-smooth feel is mainly caused by the failure of heavy calcium and ash calcium to reach a fineness of more than 400 mesh. Then how to use a simple method to check the quality of calcium ash and cement? The method is very simple. The calcium ash and cement are mixed with water into a paste, scraped onto the wall, and wiped by hand after drying. If there is hardness and no powder removal, it is authentic and qualified quality, otherwise it is counterfeit and shoddy products.
Porcelain-like putty appears small particles after polishing and calendering, which has a lot to do with the quality of polyvinyl alcohol powder. The fineness of polyvinyl alcohol powder and the quality of polyvinyl alcohol raw materials will affect the quality of imitation porcelain putty. Many domestic merchants sell 180 mesh or 200 mesh as a selling point, which is actually fooling customers. According to the international description of powder fineness, the screening rate is the standard. For example, the polyvinyl alcohol powder products produced in Japan and Taiwan are usually called S grade, and their product standard is 95%
