Polyurethane waterproof coating (referred to as JS waterproof coating), with its good physical properties, simple construction methods and construction on the wet grass, has been rapidly developed and widely used since the end of the last century to the beginning of this century. However, in recent years, this type of product has caused a great number of quality problems, which left a very bad impression on many construction units and management departments and began to be skeptical. New products are faced with poor quality eliminated products in less than a decade. The embarrassing situation is regrettable. The reason is that apart from the market's intention of sacrificing the quality and supervision of the construction process, the low-price competition manufacturers are ineffective in letting go of work and reducing the proliferation of materials. They are also related to the improper application of this product and many industry insiders' misconceptions about the product.
1. Misunderstanding of latex selection and ingredient ratio
The basic principle of JS waterproof coating is an inorganic gelling material containing cement and quartz sand as the main component modified by synthetic polymer polymer latex, and the formed coating film basically maintains the high strength and strong water resistance of the cement cement material. Based on the characteristics, its flexibility (ie, elongation) is maximized. At the same time, polymer latex also brings a negative effect, that is, the decrease of hardness and the weakening of long-term water resistance and aging resistance. The negative effect size is closely related to the type and amount of latex used (ie, the modification ability of latex). There are two main types of latex used in JS coatings on the market - polyacrylate latex and polyethylene-vinyl acetate latex. The former has better modification ability than the latter, and the former with the same performance is also significantly less than the latter, and its negative effect is also significantly less than the latter. However, most people mistakenly believe that JS coatings should be used as much as possible, and the better the amount of latex used, the more the same price is used when selecting products from different manufacturers. Therefore, some manufacturers or businesses in order to show that the amount of latex used in their products, the purchase of latex raw materials mixed with water before the preparation of JS paint, its product quality and real JS paint far, even worse, some construction teams in After low-cost contracted waterproof projects, the use of commercially available polyvinyl acetate latex (commonly known as white latex) or polyvinyl alcohol glue (commonly known as 107 glue) after the construction of the mix, the consequences can not be described, seriously damaged the reputation of JS coatings . Of the JS paints currently used extensively in construction projects, less than 10% of polyacrylic acid latexes are actually used, which is the main reason why JS paints slide into the ranks of “low-quality†products.
2, lack of understanding of the use of classification
The elongation of JS waterproof coating is directly related to the amount of latex used, but the amount of latex added directly affects the long-term water resistance of the coating. In order to solve this problem, the technical specification of the engineering specification and product standard is JS coating. Divided into two types, Type I is a large amount of latex, elongation requirements of more than 200%, for intermittent water immersion in the engineering parts (such as roof, exterior wall, etc.) to meet the larger deformation requirements. Type II uses slightly less latex and has an elongation as high as 80% to meet engineering sites (basements, toilets, etc.) that are less deformable but have long-term water resistance requirements. However, in many projects, there is no distinction between use, from the basement to There is one type of roofing, Type I or Type II, not only failing to achieve the desired effect, but also a lot of quality risks, disappointing.
3, coating thickness and the number of construction times
Even the best waterproof coating must have a certain coating thickness as a guarantee of quality. In the Technical Specifications for Roof Engineering and Technical Specifications for Underground Works, the basic thickness of JS coatings is 1.5 to 2.0 mm. In the actual project design and construction monitoring, only the number of construction times is ignored but the final thickness of the coating is ignored. It is often seen that some design drawings only indicate “the use of JS waterproof coating several coats of cloth†without indicating the thickness requirements. Site management also only cares about painting several times. For some lack of integrity of the construction team drill hole, add water to dilute the paint, the design requirements painted one or two times also get the praise of on-site management personnel, in the low-cost contract to the project can also make a lot of profit , The product with excellent performance can't stand such damage.
4, ignoring the importance of on-site mixing state of the film performance
JS coating is a two-component product. It is actually the final process of product production—mixing and phase separation, left to the on-site construction team to complete.
It is not known that the phase separation of two-component products is critical to the formation of film properties, and that the addition of JS coatings to powder-liquid two-components is not as easy as the mixing of other liquid-liquid two-component products. The manufacturer's product manuals have explained the correct method of on-site mixing. However, many of the construction team's mixing process is perfunctory. Some even do not have a dedicated stirrer, and the on-site sticks are manually stirred and mixed. A very small number of people know the judgment and mastery of the “phase end pointâ€, and the performance of the final molded film is greatly compromised because of incomplete mixing and phase separation.
5, the misunderstanding of the tensile strength
In the JS coating product standard, the tensile strength requirements for the coating film are I type ≥ 1.2MPa, type II ≥ 1.8MPa, many people mistakenly believe that the higher the tensile strength, the better, in fact, otherwise, in the JS coating stretching Among the performance test methods, there is a standard curing process of heating and curing at 50°C for 24 hours after 7 days. Many paint products are rapidly growing in tensile strength due to the migration of plasticizer during heat curing at 50°C, indicating that these products are exposed. The use of heat aging in the performance changes quickly and does not last long. Therefore, products with abnormally high tensile strength should be vigilant. If necessary, heat aging retention test can be done. Rather than unilaterally thinking that the higher the tensile strength, the better.
6, randomly set the base position
In some engineering details of the joints, in order to avoid stress concentration, additional carcass layers are used to extend the dispersion stress and reduce cracking of the coating. Therefore, the position of the tire base directly affects the use effect. It should be that the closer the tread base is to the base layer, the more it can achieve the effect of decentralized stress. Actually, many projects randomly set the position of the tire base uninterested to set it in the middle of the coating. In some projects, the foundation of the tire is laid on the surface of the coating. I once found this phenomenon at a construction site and asked why the construction workers exposed the foundation to the surface. The coworkers answered: “The money for the foundation will be settled with the employer,†the order People are ridiculous.
7, one-sided understanding "can be in the wet base construction."
JS waterproof coating is more than other waterproof coating features can be used in the wet base construction, there is a problem of the degree of moisture, not that any humid climate conditions or very high primary moisture content can be constructed under the circumstances, because JS coating latex Is cured by volatilization, too high base layer moisture content and too humid climatic conditions on the latex curing film is unfavorable, will reduce the coating elongation. At the same time, the cement in JS coating is cured by hydration. The base layer and weather conditions that are too dry are not good for cement curing. Therefore, during the hot dry season, some water should be sprayed on the base layer before construction. In fact, JS coatings still have some requirements on the temperature and humidity range of construction. Generally, the temperature is between 5°C and 35°C, and the humidity is between 50% and 70%. It is suitable for construction regardless of temperature and humidity conditions, although it can also form a film. However, the performance of coating film is far away.
8, misunderstanding of the deployment of water can be added
Most of the manufacturers stated in their product specification that when the first pass is applied, water can be added to dilute the paint to improve the penetration of the base layer and increase the adhesion to the base layer. Therefore, many people misunderstood that JS coating is free to add water, which is very harmful, JS coating two component ratio - poly ash ratio (polymer to cement ratio) and water-cement ratio (water and cement ratio ) is determined by the manufacturer through multiple tests and development. The effect of arbitrarily changing one of the components is much greater than the performance of the coating film. The phenomenon of increasing the amount of powder and then adding water to adjust the consistency in the actual project is abound. Many projects are using the name of JS paint to steal materials, so that the application of JS paints is very uncertain.
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