HC Chemical Network News: Polymer cement waterproof coating (referred to as JS waterproof coating), with its good physical properties, simple construction methods and construction on wet base, etc., has been rapidly developed since the end of the last century and a wide range Promote the application. However, in this process, there are some quality problems in the application of this type of product. The reason for this is not only the unqualified product quality, but also the misuse of this product. Many people in the industry are concerned about the misunderstanding of this product.
1. Misunderstanding of the choice of latex and the ratio of ingredients
The basic principle of JS waterproof coating is the inorganic cementitious material with synthetic polymer latex latex modified cement and quartz sand as the main component. The formed coating film basically maintains the high strength and strong water resistance of cement cementitious materials. On the basis of it, it has flexibility (ie elongation). However, polymer latex also has a negative effect on cement-based materials, that is, the decrease in hardness and the long-term water resistance and aging resistance are weakened. The magnitude of the negative effect is closely related to the type and amount of latex used (ie, the modification of latex). Sexual ability). At present, there are two main types of latex for JS coatings on the market: polyacrylate latex and polyethylene-vinyl acetate latex. The former has better modification ability than the latter, and the former performance is also significantly less than the latter. Its negative effect is also significantly smaller than the latter. However, most people mistakenly believe that the JS coating should be the larger the amount of latex. The choice of different manufacturers is based on the same price as the product. Therefore, in order to show that the amount of latex in the product is large, some manufacturers or merchants will mix the purchased latex raw materials with water and then prepare JS coatings. The quality of the products is far from the real JS coatings. What's more, some construction teams use the commercially available polyvinyl acetate latex (commonly known as white latex) or polyvinyl alcohol glue (commonly known as 107 glue) after the low-cost contracting waterproof project, and the consequences are unimaginable. The ground damages the reputation of JS coatings. At present, less than 10% of the JS coatings used in construction projects are actually made of polyacrylate latex.
2. Insufficient understanding of classification
The elongation of JS waterproof coating is directly related to the amount of latex used, but the amount of latex directly affects the long-term water resistance of the coating. In order to solve this contradiction, the technical treatment of engineering specifications and product standards is to classify JS coatings: Type I is a large amount of latex, and the elongation requirement is more than 200%. It is used for intermittent water-immersed engineering parts (such as roofing and exterior). Wall surface, etc.) to meet the requirements of large deformation; type II is a little less than the amount of latex, the elongation rate is as long as 80%, to meet the deformation of the project site with long-term water resistance requirements (basement, toilet room, etc.) . However, it is not used in many projects. From the basement to the roof, one type (type I or type II) is used, which not only fails to achieve the expected results, but also causes many quality hazards.
3. Relationship between coating thickness and construction times
Even the best waterproof coatings have to have a certain coating thickness as a quality guarantee. In the "Technical Specifications for Roofing Engineering" and "Technical Specifications for Underground Engineering Waterproofing", the basic thickness of JS coatings is 1.5 to 2.0 mm. However, in the design and construction monitoring of actual engineering, often only pay attention to the number of constructions but ignore the final thickness of the coating. It is often seen that some design drawings only indicate “several coatings with JS waterproof coating†but no thickness requirements. And the on-site management only cares about painting a few times. This will give some construction teams that lack integrity and have the space to drill. After the paint is diluted with water, it will be painted one or two times more than the design requirements. It will also be praised by the on-site management personnel. To the high profits.
4. Ignore the importance of the effect of on-site mixing on film properties
JS coating is a two-component product. In fact, the final process of product production, mixing and phase separation, is left to the on-site construction personnel. It is not known that the phase separation state of the two-component product is critical to the formation of coating properties. JS coating is a powder-liquid two-component, which is not as easy to mix as other liquid-liquid two-component products. Although the product specifications of each manufacturer indicate the correct method for on-site mixing, many construction team mixing processes are perfunctory. Some even don't have a special agitator. On the spot, the root stick is hand-mixed a few times. Very few people know the judgment and mastery of the "phase separation end point", so that the performance of the final formed film is large because of the incomplete phase separation. discount.
5. Misunderstanding of tensile strength
In the product standard of JS coating, the tensile strength requirements of the coating film are I type ≥ 1.2 MPa and type II ≥ 1.8 MPa, respectively. Many people mistakenly believe that the higher the tensile strength, the better, but it is not. In the tensile performance test method of JS coating, there is a standard curing process of heating at 50 ° C for 24 hours after curing for 7 days. Many coating products have a rapid increase in tensile strength due to the volatilization and migration of plasticizers in the process, indicating that these products The heat aging performance changes rapidly and the life is not long during exposure. Therefore, the product with abnormally high tensile strength should be alert, and if necessary, the heat aging retention test can be performed, and it should not be considered that the higher the tensile strength, the better.
6. Feel free to set the base position
In the details of the joints of some projects, in order to avoid stress concentration, the base layer is added to spread the dispersion stress and reduce the cracking of the coating. Therefore, the setting of the base position directly affects the use effect, and the closer the base is to the base layer, the more the dispersion stress can be achieved. In fact, many projects randomly set the position of the tire base without any problem, so as to set it in the middle of the coating. Some projects have placed the base on the surface of the coating.
7. One-sided understanding "can be applied in wet base"
Compared with other waterproof coatings, JS waterproof coatings can be used in wet base construction, but there is also a problem of humidity. It is not that any wet climatic conditions or very high base water content can be applied because JS coating latex It is cured by volatilization. Excessive base layer moisture content and too humid climatic conditions are unfavorable for the solidification of the latex film, which will reduce the elongation of the film. At the same time, the cement in JS coating is solidified by hydration. The too dry base layer and climatic conditions are not good for cement solidification. Therefore, it is necessary to spray some water on the base layer before construction in the hot and dry season. In fact, JS coatings still have some requirements for the temperature and humidity range of the construction. Generally, the temperature is 5 to 35 ° C, and the humidity is 50% to 70%. It is suitable to construct JS coating regardless of temperature and humidity conditions, although it can also form a film. However, the film properties are quite different.
8. Misunderstanding of water blending
Most manufacturers have stated in their product specifications that water can be added during the first application to dilute the coating to improve the penetration of the substrate to improve the adhesion to the substrate. Therefore, many people misunderstand that JS paint is free to add water, which is wrong. The ratio of two components in JS coating - the ratio of polymer to cement (the ratio of polymer to cement) and the ratio of water to cement (the ratio of water to cement) are determined by the manufacturer through repeated experimental studies, and any one of the components is arbitrarily changed. The impact of performance is great. In the actual project, the phenomenon of increasing the amount of powder and then adding water to adjust the consistency is everywhere. This is actually the practice of stealing materials by the name of JS coating.
Editor in charge: Chen Xiaohui
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