Common problems in the application of real stone paint and preventive measures
Real stone paint is a kind of popular decorative paint for exterior wall because of its strong decorative property, wide application, good durability and non-fading. In the construction and application of true stone paint, there are often some problems affecting the quality and decorative effect, which have a certain universality. These problems are sometimes caused by improper selection of raw materials and formulation design, and some are caused by improper construction methods. This paper discusses these problems from the angle of formula and material.
1. The coating is too soft.
The quality of the real stone paint should be very hard, nail can not be moved. If you can still use your nails for three days in good weather, you should think of the coating as too soft. The reason why the real stone paint is too soft is that the emulsion is inappropriate. Many manufacturers, when preparing genuine stone lacquer, take the same emulsion as making latex paint, which is wrong. The content of emulsion in the real stone paint is low. When the film is formed, the coating is not tight enough because of the existence of a large amount of sand and gravel. Therefore, the emulsion with high cohesive force and the lowest film forming temperature should be selected.
According to the study, the bonding strength of the emulsion used for genuine stone paint should not be lower than 3MPa, and the minimum film forming temperature should not be less than 20 degrees Celsius. The higher minimum film forming temperature may cause the disadvantage that it is difficult to form film at lower temperature, which can be solved by adding more film forming additives. The film forming agent can be completely evaporated after drying, and generally does not affect the performance of the coating. At present, the use of more alcohol and fat -12 in the production of water emulsion paint also has a good effect in the use of real stone paint. The dosage is generally one hundred parts of the emulsion added five parts, and winter is appropriate to add more.
2. The coating is white with water.
The acrylate emulsion used as film builder of dry stone paint should have good water resistance after drying. Therefore, it is not necessary to whiten the coating after drying. However, some of the true stone paint coatings will whiten after each rain, the coating becomes loose, and after the rain stopped, after the sun, the coating restored to its original color. After analysis, this is due to the poor water resistance of the coating and the absorption of moisture. From the analysis of the structure of polyacrylate, the real lacquer coating should have good water resistance. However, due to the addition of surfactants when acrylic emulsion is synthesized, some manufacturers use excessive surfactants to increase the stability of the emulsion. Some manufacturers add carboxymethyl cellulose, hydroxyethyl cellulose and other substances as thickeners when preparing genuine lacquer, and add sodium benzoate as preservative. These substances are water-soluble or hydrophilic. The water resistance of the coatings is greatly reduced when the coatings are left in the coatings after film forming. Experiments showed that the pure acrylic emulsion mixed with quartz sand without any auxiliaries, the water absorption rate of the sprayed coating was 0.42%, and the water absorption rate increased to 4.3% on the basis of the above coating by adding 0.4% hydroxyethyl cellulose. Because the coating of the true stone paint is thicker, once absorbed moisture, it is not easy to release in a shorter time, resulting in the appearance of whitening, the result of the internal loosening of the coating.
In order to solve the above problems, we can improve the raw materials and formula. First of all, excellent quality emulsion should be selected. The silicone modified acrylate emulsion (silicone acrylic emulsion) developed in recent years has good hydrophobicity and can effectively resist water intrusion. Secondly, special thickeners should be selected. Thickening agent has good thickening effect and less consumption, so it will not cause great changes in coating properties. At present, there are many thickeners in the market, such as German Henkel company and Taiwan de Qian company. Preservatives should also be selected as special materials.
Recently, some customers have added silicone waterproofing solution to the real stone paint which is currently available in the market, and received unexpected good results. Rainwater droplets on the surface of the coatings and does not penetrate into the coatings, making the true stone paint both decorative effect and waterproof function.
3. Too much sand when spraying.
Some genuine lacquer drops more sand during spraying, which can reach 1/3 when serious, resulting in waste. In addition to the reasons for construction, raw materials and formulations may also cause the above phenomenon. At present, there are two kinds of sand for genuine stone paint, artificial sand and natural sand. It has been observed that the real stone paint made from natural sand is two less than artificial sand. This may be related to the hardness and surface state of sand. Generally speaking, it is easy to sand out when the sand with high hardness and smooth surface is used. In addition, the gradation of sand is also very important when preparing genuine stone paint. The proper gradation of genuine stone paint is less than that of spraying, and the coating is more compact. Therefore, it is suggested that natural sand should be used as much as possible when preparing genuine stone lacquer, and the sand must be graded. The results show that the use of the following gradation, the construction of less sand, coating quality is also good: particle size greater than 5%, 10-15 mesh between 25%, 50-100 mesh 50%, less than 100 mesh 20%.
In addition, the consistency of the coating also has a certain effect on the sand loss during spraying. The paint is too thick when the construction is difficult, too thin sand on the wall when the initial viscosity is too low, will cause sand to fall. Therefore, it is helpful to improve the consistency of the coating as much as possible to solve the problem of sand loss in the case of no difficulty in construction.