Application of exterior wall insulation finishing coating?

What are the applications of exterior wall insulation finishing coatings? The following Zhongda Consulting and Bidding Teachers will answer your questions for your reference.

Exterior wall insulation is currently the most effective way to achieve energy conservation in buildings. As the application of exterior wall finishing materials, architectural coatings are the first choice. According to the national JG149-2003 "Expanded polystyrene board thin plaster exterior wall external insulation system" regulations, the coating must have good compatibility with the thin plaster exterior insulation system, and the performance indicators should comply with the relevant standards for exterior wall building coatings . In addition to achieving effective energy saving and ideal decorative effects, there are other issues that should be paid attention to when choosing coatings for exterior wall insulation finishes.

To understand the systematic application of exterior wall exterior insulation coatings, you should first understand the composition and structure of the exterior wall exterior insulation system, which are, in order, structural wall, bonding layer, insulation layer, plaster, and Fiberglass mesh, facing layer. The bonding layer is generally composed of bonding glue, and rivets can be added if necessary. If the base surface does not meet the bonding requirements, it needs to be fixed mechanically. The insulation layer is generally flame-retardant polystyrene foam board (EPS) or extruded polystyrene board (XPS). The thickness is selected according to local energy-saving requirements. The protective layer is composed of plaster glue and fiberglass mesh. For the facing layer, exterior wall coatings with better anti-cracking, water repellency, air permeability and weather resistance can be used. At present, common problems in the domestic promotion and application of external insulation systems are surface cracking, hollowing and water seepage. Cracked and leaking exterior wall insulation has a worse impact than no exterior wall insulation and is difficult to repair. The protective layer is the key to determining the performance of the entire external insulation system. Once the protective layer is completed, the crack resistance of the external wall insulation is basically guaranteed.

The compatibility between various materials and components and the integrity of the entire system

Solvent-based coatings cannot be used in exterior wall insulation systems. Because the external wall insulation system generally uses polystyrene (EPS, XPS) or polyurethane (PU) as the insulation layer, according to the principle of similar miscibility, solvent materials such as benzene and toluene can dissolve polystyrene, butyl acetate and Xylene, etc. can dissolve polyurethane. Solubility parameters of some materials. In the external wall insulation system, the amount of polystyrene and polyurethane insulation layers eroded by solvent-based coatings is related to factors such as the thickness and porosity of the protective layer, the solvent's solubility, volatilization rate and quantity. It is often seen that the polystyrene insulation layer is eroded and the surface of the exterior wall insulation system is uneven. It is the No. 200 solvent oil commonly used in water-based coatings. The aromatic hydrocarbons can also dissolve the polystyrene insulation layer. Therefore, its content needs to be controlled based on actual usage.

Water repellency and breathability of coatings

National standard JG149-2003 "Expanded polystyrene board thin plastered exterior wall external insulation system" stipulates that the 5mm thick protective layer of the external insulation system , immersed in water for 24 hours, the water absorption should be ≤500g/㎡; the water vapor moisture flow density of the protective layer of the external insulation system and the decorative coating must be ≥0.85g/(㎡.h) in JGJ144-2004 "Technical Regulations for Exterior Wall Insulation Engineering" 》This provision is somewhat different. According to the regulations in JG149-2003, for exterior walls, in terms of water absorption, the outer layer is generally required to be lower than the inner layer, which means that the exterior coating should be lower than the protective layer, that is, the water absorption of the coating should be less than 500g/㎡, so that less water can enter the wall; in terms of water vapor wet flow density, the outer layer is generally required to be higher than the inner layer, which means that the exterior coating should be higher than the protective layer, that is, the water vapor in the coating The wet flow density must be much greater than 0.85g/(㎡.h) so that water vapor can be discharged unimpeded.

In contrast, in the European standard EN1062-1 to 2002 "Classification of external coatings and coating systems for paints and varnishes, plaster layers and concrete bases - Class 1", according to the water vapor permeability of the coating External coatings and coating systems are classified and graded according to their properties, water absorption, etc. to facilitate user selection.

Although JG149-2003 and EN1062-3 than the 1998 "Classification of external coatings and coating systems on painted and varnished plaster layers and concrete base surfaces-3 Determination and classification of water absorption" have a higher limit on water absorption. The test methods are slightly different, mainly because the base layer is different. To make a rough comparison between them, the 24h water absorption of 500g/㎡ is equivalent to W=0.1kg/㎡h0.5, which is the lowest level of water absorption in the European standard EN1062-1, and also That is to say, it is the most stringent requirement.

In terms of water absorption and impermeability, elastic coatings, glossy coatings, water-based metallic paints and lotus king coatings can generally meet the requirements, but a considerable number of coatings cannot meet this requirement, and some Paint must be used with certain primers to meet the requirements.

The water vapor wet flow density in the JG149-2003 standard is measured according to the water method in GB/T17146-1997 "Test Method for Water Vapor Transmission Performance of Building Materials", which is measured by the relative density of water. The difference between humidity 100 and laboratory relative humidity produces a flow of water vapor. The test method of ENISO7783-2 to 1999 "Classification of exterior coatings and coating systems on painted and varnished plaster layers and concrete base surfaces - 2. Determination and classification of water vapor permeability" is different from GB/T17146-1997. It generates water vapor flow due to the difference between ammonium dihydrogen phosphate relative humidity of 23°C and laboratory relative humidity of 93‰ and laboratory relative humidity of 50‰. Strictly speaking, results obtained from different test methods cannot be compared. Roughly speaking, the water vapor wet flow density of 0.85g/(㎡.h) is equivalent to V=20.4g/㎡d, which is equivalent to the resistance of the still air layer of 1.2m, which belongs to the medium water vapor permeability in the European standard EN1062-1. The wet flow density of coating water vapor is too low, which may cause surface color difference in the mild case, mold and poor thermal performance in severe cases, or even damage to varying degrees. For water vapor permeability, elastic coatings are difficult to meet the requirements, but silicone coatings and other coatings can meet the requirements for water vapor flow density. In addition, the water vapor flow density is not only related to the coating, but also inversely proportional to the thickness of the coating film.

For the external wall insulation system, its water absorption capacity (water repellency) and water vapor flow density (breathability) must be satisfied at the same time, so a comprehensive balance must be achieved. From the perspective of water repellency and breathability, the JG149-2003 standard has much higher requirements for exterior wall insulation finishing coatings than ordinary exterior wall coatings. Some exterior wall coatings that meet the requirements of product standards do not meet this requirement, and some can pass The coating system paired with the primer is solved. Durability of coatings JGJ144-2004 "Technical Regulations for Exterior Wall Insulation Engineering" stipulates that the service life of exterior wall insulation projects should not be less than 25 years. The service life of exterior wall paint is not only related to the quality of exterior wall paint, but also to factors such as the base layer, construction, environmental conditions of use, color used, and maintenance. Generally it is about 8 to 15 years, and there are also reports of service life up to 30 years. Therefore, exterior wall coatings with good durability should be used as much as possible, especially color pastes. Inorganic color pastes with good color retention should be given priority. In addition, maintenance and renovation should be done in a timely manner.

Color of paint

The color of paint mainly involves the absorption and reflection of solar energy. When solar radiation energy is incident on the opaque coating surface, part of the energy is absorbed, the other part of the energy is reflected, and the transmitted energy is negligible. The ratio of absorbed energy to the total incident energy is called the coating’s absorption coefficient (α); the ratio of the reflected energy to the total incident energy is called the coating’s reflection coefficient (ρ) α ρ = 1. The absorption coefficient and reflection coefficient vary with It changes with the coating temperature and the wavelength of the incident radiant energy. The relationship between color and solar radiation energy reflection coefficient, the particle size of these pigments is not larger than 50μm.

As for the requirements for exterior wall insulation finishes, we hope to reflect more of the sun’s heat energy in summer. And hope to absorb more solar energy in winter. Generally speaking, there are three types of heat transfer: conduction, convection, and radiation. Solar radiant heat is the main heat source affecting the thermal process of buildings. In summer, the temperature is high and the radiant heat is large. In addition, the density of the insulation layer is low, the heat insulation is poor, and the color of the coating has a great impact. In winter, the temperature is low, there is less radiant heat, the thermal conductivity of the insulation layer is low, and the color of the coating has little impact.

Therefore, the choice of exterior wall insulation finishing paint color should be based on summer insulation. In other words, you cannot choose a color that is too dark. For example, the minimum brightness value should be greater than 20‰.

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