Principles to be followed in the selection of exterior wall coating
The coating selected for the exterior wall shall have good aging resistance, water resistance, color retention, pollution resistance, and good adhesion, etc.; it is strictly prohibited to use the coating for the interior wall for the exterior wall, and it is required to have high frost resistance in the cold and frozen north; the coating with fast drying and initial water resistance shall be selected for the construction in rainy season; the coating with low film forming temperature shall be selected for the construction in winter; the wall with cement mortar shall be Choose the coating with high alkali resistance
I. solvent coating
Solvent based coating is a kind of volatile coating, which is made up of polymer synthetic resin as the main film-forming material, organic solvent as diluent, adding a certain amount of pigments, fillers and additives, mixing, dissolving and grinding. After brushing on the outer wall, with the volatilization of the solvent contained in the coating, the film-forming substance and other non-volatile components together form a uniform and continuous film, that is, the coating.
As the coating is relatively tight, it usually has good hardness, luster, water resistance, acid and alkali resistance, good weather resistance, pollution resistance and other characteristics. However, due to the volatilization of a large number of easily resistant organic solvents during construction, it is easy to pollute the environment. The film has poor air permeability and hydrophobicity. If it is constructed on a wet base, peeling and falling off are easy to occur. Because of these reasons, the consumption of such exterior coatings at home and abroad is lower than that of emulsion type exterior wall coatings. In recent years, the solvent based acrylic exterior wall coating developed has outstanding weatherability and decoration, with a service life of more than 10 years and a short construction period, and can be used at a lower temperature. Foreign countries have good weather resistance, waterproof, and high elastic polyurethane exterior wall coating, with a durability of more than 15 years.
The main type of solvent coating is perchloroethylene exterior wall coating, which is one of the earliest types of synthetic resin coating used in building exterior wall decoration in China. Perchloroethylene resin is the main film-forming material of perchloroethylene exterior wall coating. A solvent type exterior wall coating is made by kneading, mixing, plasticizing, pelletizing, dissolving and filtering with a small amount of other resins and adding plasticizers, stabilizers, fillers, pigments and other materials. The external wall coating of perchloroethylene has the characteristics of fast drying, convenient construction, good weather resistance, strong chemical corrosion resistance, good water resistance and mildew resistance, but its adhesion is poor, so it is necessary to select appropriate synthetic resin to enhance its adhesion when preparing. Perchloroethylene resin has poor solvent release, so although the surface drying of the film is very fast, it is very slow to fully dry, and only after it is completely dry can it become hard to peel. The main film-forming material is perchloroethylene resin, and the amount used in the coating is about 10%. Alkyd resin, phenolic resin, propionic acid resin, maleic anhydride resin and other synthetic resins are often added to improve the adhesion, luster, fullness, durability and other properties of perchloroethane exterior wall coating.
Dibutyl phthalate is commonly used as plasticizer in perchloroethylene (PCE) exterior wall coating, and its addition amount is about 30% - 40%. Perchloroethylene resin is easy to cause resin decomposition under the action of light and heat. The purpose of adding stabilizer is to prevent resin decomposition and extend the life of coating. The commonly used stabilizers are lead dibasic phosphite, the dosage is about 2%. Other stabilizers include barium ricinoleate, barium carbonate, ultraviolet absorber UV-9, etc. Commonly used pigments and fillers include zinc oxide, titanium dioxide, talcum powder, etc.
Choose the coating from the classification of the used parts of the coating
The new building coatings are classified according to their application parts, including exterior wall, interior wall, ceiling and ground building coatings. According to the base materials used in the coating, it can be divided into three categories: inorganic, organic and inorganic organic composite building coatings. Organic coatings are also divided into three basic types: water soluble, solvent based and water-borne emulsion type.
Inorganic coating is made up of basic silicate, hardener, pigment, filler and assistant. When inorganic coating is selected for the exterior wall facing, silica sol inorganic building coating shall be selected preferentially instead of lime slurry coating. The water-soluble coating is made up of water-soluble resin as film-forming material and a certain amount of pigments and fillers. Because the exterior wall is directly exposed to rain, it is not suitable for the exterior wall. No more details
Solvent based coating is a kind of volatile coating, which is made of polymer synthetic resin as film-forming material, organic solvent as diluent, pigment, filler and other auxiliary materials. Chlorinated rubber coating, acrylic resin coating and polyurethane coating shall be preferred when such coating is selected for exterior wall facing. Perchloroethylene coating, styrene coating and polyvinyl butyral coating can be selected. Paint shall not be used as finish.
Two. Emulsion paint
The exterior wall coating with polymer synthetic resin emulsion as the main film forming material is called emulsion type exterior wall coating. According to the different methods of emulsion manufacturing, they can be divided into two categories: one is the emulsion synthesized directly by monomer polymerization through emulsion polymerization; the other two is emulsion made from polymer synthetic resin through emulsification. According to the texture of paint, it can be divided into latex paint (thin emulsion paint), thick paint and colored sand wall paint.
At present, most emulsion type exterior wall coatings are made from emulsion polymerization as the main film forming material. The main features of emulsion exterior wall coatings are as follows:
(1) with water as the dispersing medium, there is no flammable organic solvent in the coating, so it will not pollute the surrounding environment, and it is not easy to cause fire, and has little toxicity to human body;
(2) the construction is convenient, which can be brushed, rolled or sprayed, and the construction tools can be cleaned with water;
(3) the paint has good air permeability and contains a lot of moisture, so it can be applied on the slightly wet base, which is very suitable for the application of construction site;
(4) the exterior emulsion coating has good weatherability, especially the high quality acrylic exterior wall emulsion paint. Its properties such as brightness, weatherability, water resistance and durability can be comparable to those of solvent based acrylic exterior wall coatings.
(5) the main problem of emulsion type exterior wall paint is that it can not form high-quality coating at too low temperature. Usually, it must be constructed at above 10 C to ensure the quality, so it is not suitable for winter.
Waterborne emulsion coatings are made from synthetic resins, which are dispersed in water by tiny particles and form heterogeneous emulsion. When this type of coating is selected for the exterior wall facing, the acrylic coating is the most popular in the world. Tbs-86 organic and inorganic composite coating and jh85o4 concave and convex pattern Xu material are used for exterior wall facing.
1. Styrene acrylic emulsion coatings
Styrene acrylic emulsion coating is a latex exterior wall coating made of styrene acrylate copolymer emulsion (mainly styrene acrylic emulsion) as main film-forming material and added with pigment, filler and auxiliaries.
The coating made of pure acrylate emulsion has excellent weatherability, light retention and color retention, and is suitable for exterior wall coating. But the price is expensive, which limits its use. Styrene acrylic emulsion coatings made of some or all styrene instead of methyl methacrylate in pure acrylic emulsion still have good weatherability and light and color retention, but the price is greatly reduced. Benzene - C coating also has excellent alkali resistance, water resistance, delicate appearance, bright color, good texture, very suitable for external wall coating. From the analysis of resources and cost, it is an exterior wall emulsion coating suitable for China's national conditions. At present, the domestic production is large. Various types of exterior wall emulsion coatings prepared by using styrene acrylic emulsion are superior to those of B - acrylic emulsion. It is used for the preparation of glossy paint, the gloss is higher than that of B - acrylic coating, and because of the good pigment binding ability of the styrene acrylic emulsion, it can be used to prepare the interior paint with high pigment volume.
Drying time, surface dry solid content water resistance, 23 ± 2 ℃, 96h alkali resistance, saturated Ca (OH) 2, 48h scrub resistance, 0.5% soap solution, 1000 times stain resistance (white and light color), 5 times cycle reflection coefficient reduction rate freeze-thaw stability, - 5 ± 1 ℃, 16h, 23 ± 2 ℃ 8h, 3 times cycle 2h12h45% non foaming, no falling off, slightly discoloration is allowed to be the same as that of non exposed bottom < 10%.
2, B / C emulsion coatings
B - acrylic emulsion thick coating is a thick outer wall coating made of vinyl acetate acrylic copolymer emulsion as the main film forming material and mixed with a certain amount of coarse aggregate. The decorative effect of the coating is good. It belongs to the middle grade exterior wall coating, with a service life of 8-10 years. B - acrylic emulsion thick coating has the advantages of thick film, good texture, weather resistance, water resistance, good freeze-thaw stability, good color retention, strong adhesion, fast construction speed and easy operation.
3. Color sand wall exterior wall coating
Colored sand wall exterior paint, also known as colored sand coating, is made of synthetic resin emulsion and coloured aggregate as main body, thickening agent and various auxiliaries. Due to the use of high-temperature sintered color sand, color ceramics or natural colored stone chips as aggregates, the coating has rich color and texture, and its color retention and weather resistance are greatly improved compared with other types of coating. The durability is more than 10 years.
Drying time solid content water resistance, soaking for 500h alkali resistance, saturated Ca (OH) 2500h freeze-thaw test, 50 cycles ≤ 30min ≥ 50%, no abnormal aggregate settlement rate, drying time low-temperature stability, - 5 ℃ heat resistance, 60 ℃ constant temperature 8h freeze-thaw cycle, 30 normal temperature storage stability, 3-month bond resistance, 500h alkali resistance, 300h acid resistance, 300h aging resistance, 250h < 10% < 2H constant consistency No abnormality, no deterioration, 5kg / cm2, no abnormality, no abnormality, no abnormality
III. inorganic polymer coating
Inorganic polymer building coating is a new type of building coating developed in recent years. Alkali silicate and silica sol are widely used in architecture.
Organic polymer building coatings generally have the disadvantages of poor aging resistance, poor heat resistance and small surface hardness. Inorganic molecular coating has good properties in these aspects, such as aging resistance, high temperature resistance, corrosion resistance, durability, etc., high hardness and wear resistance of the coating. If the material is reasonable, the water resistance is good, and the source of raw materials is wide and the price is cheap, so in recent years, it has been widely valued and developed rapidly at home and abroad. The following describes the situation of silica sol coating.
Silica sol exterior wall coatings are colloidal silica (silica sol) as the main film forming material, organic polymer emulsion as auxiliary film forming material, adding pigment, fillers and auxiliaries, stirring, grinding and modulating water dispersible coatings.
(1) water is used as the dispersion medium, which is non-toxic, odorless and does not pollute the environment.
Avoid mixing paint:
The coating shall be applied with appropriate consistency. However, if the water is not stirred evenly, it will be added at will, and the color will be different after spraying, and the powder will be dropped and hollowed out. If it is necessary to add water, it shall be carried out according to the product description. It is not allowed to add water at will, to increase the color of the paint at will, to blindly purchase the pigments on the market, and to add color to the paint. Although the color meets the requirements during construction, but after adding color without permission, certain chemical components in the paint are damaged, leading to incorrect color of the facing and poor color retention performance. In addition, the transportation and storage of the coating must conform to the product description. During construction, unqualified, deteriorated and privately processed coatings shall not be used.
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