Common Problems Encountered During the Construction Process of Real Stone Paint Coatings
Some real stone paints lose a lot of sand during spraying, which can reach about 1/3 in severe cases, causing waste. In addition to construction methods, the raw materials and formulas may also cause the above phenomenon. Currently, there are two types of sand used for real stone paint: artificial sand and natural sand. Observations show that real stone paint made with natural sand has less sand loss compared to that made with artificial sand. This may be related to the hardness and surface condition of the sand. Generally speaking, using sand with higher hardness and a tighter, smoother surface tends to result in more sand loss. Additionally, the grading of the sand is also very important when preparing real stone paint. Properly graded real stone paint not only has less sand loss during spraying but also has a tighter coating. Therefore, it is recommended to use natural sand as much as possible when preparing real stone paint and to ensure that the sand has a certain grading. Furthermore, the viscosity of the paint also has a certain impact on sand loss during spraying. If the paint is too thick, it is difficult to apply; if it is too thin, the initial adhesion of the sand to the wall is too low, both of which will cause sand to fall off. Therefore, under conditions where construction is not difficult, it is advisable to increase the viscosity of the paint as much as possible to help solve the sand loss problem.
A good quality real stone paint coating should be very hard, and cannot be scratched with a fingernail. If after three days of construction in good weather, it can still be scratched with a fingernail, it should be considered that the coating is too soft. The main reason for the softness of real stone paint is the inappropriate choice of emulsion. Many manufacturers use the same emulsion for preparing real stone paint as they do for preparing latex paint, which is incorrect. The emulsion in the real stone paint formula has a lower content, and due to the presence of a large amount of sand and gravel during film formation, the coating is not dense enough. Therefore, it is necessary to choose an emulsion with higher adhesion and a higher minimum film formation temperature. Research indicates that the adhesion strength of the emulsion used for preparing real stone paint should not be lower than 3 MPa, and the minimum film formation temperature should not be lower than 20°C. A higher minimum film formation temperature may cause difficulties in film formation at lower temperatures, which can be resolved by appropriately adding film-forming aids. Film-forming aids can completely evaporate after the coating dries and generally do not affect the performance of the coating. Currently, a commonly used film-forming aid in water-based coatings is 12, which also has good effects when used in real stone paint, typically added at a rate of 5 parts per hundred parts of emulsion. In winter, it can be added in slightly larger amounts.
The acrylic emulsion used as a film-forming aid for real stone paint should have good water resistance after drying, so the coating should not turn white when it encounters water after drying. However, some real stone paint coatings turn white after each rain, and the coating becomes loose, but after the rain stops and the sun shines, the coating returns to its original color. Analysis shows that this is due to poor water resistance of the coating, which absorbs moisture. Analyzing from the structure of polyacrylic acid, the real stone paint coating should have good water resistance. However, since surfactants need to be added during the synthesis of acrylic emulsions, some manufacturers greatly exceed the amount of surfactants used to increase the stability of the emulsion; some manufacturers add cellulose ether and other substances as thickeners when preparing real stone paint, as well as sodium benzoate as a preservative. These substances are either water-soluble or hydrophilic, and when left in the coating after film formation, they greatly reduce the water resistance of the coating. Experiments show that mixing pure acrylic emulsion with quartz sand without any additives results in a coating with a water absorption rate of 0.42%; however, adding 0.4% cellulose ether to the above coating increases the water absorption rate to 4.3%. Due to the thickness of the real stone paint coating, once it absorbs moisture, it is not easy to release it in a short time, resulting in a white appearance and a loose internal structure. To solve the above problems, improvements can be made to the raw materials and formulas. First, high-quality emulsions should be selected. Recently developed silicone-modified acrylic emulsions (silicone-acrylic emulsions) have good hydrophobic properties and can effectively resist moisture intrusion. Secondly, specialized thickeners should be chosen. Good thickeners have a good thickening effect and require a small amount, so they will not cause significant changes in the performance of the coating. There are many thickeners available on the market. Preservatives should also be specialized materials. Recently, adding commercially available silicone waterproofing liquids to real stone paint has yielded unexpectedly good results. Rainwater beads up on the surface of the coating and rolls off without penetrating the coating, allowing the real stone paint to have both decorative effects and waterproof functions.
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