Promote building exterior insulation in practice

The construction project J4 technical letter window promotes exterior insulation of building exterior wall in practice Zhang Zhihua (Funing Construction Bureau of Qinhuangdao City, Hebei Province, Qinhuangdao 066000, Hebei Province) According to the reality of energy shortage in China, the necessity of promoting building energy-saving is expounded. The problems and causes of the energy-saving houses built using external thermal insulation technology have made some suggestions.

With the rapid development of the national economy, energy shortages have become the main contradiction that restricts China’s economic development. Building energy efficiency is a key link in alleviating the contradiction of energy shortage in China, improving the quality of people's living environment, reducing environmental pollution, and achieving the strategic goal of sustainable development. Promoting building energy efficiency will be a long-term national policy for the development of residential construction in China. JGJ26-95 energy saving standard for civil buildings (heating residential building part) requires new residential buildings to save heating energy consumption by 50%, of which 30% rely on improving the insulation performance of building envelope structure, and 20% rely on heating boilers and outdoor supply Heat pipe network efficiency to achieve.

To promote energy efficiency in buildings, the main purpose is to improve the insulation performance of the building envelope structure (including walls, doors, windows, roofs, floors, etc.). In the building envelope structure, the wall has the largest proportion of heating energy consumption, accounting for 32.1% of the total energy consumption, and 36.2% of the total energy consumption. Therefore, the reform of the building wall and the development of the wall energy-saving technology is one of the most important building energy-saving technologies. The important part. The development of external wall insulation technology is the main way to achieve energy efficiency in buildings. At present, China's external wall insulation is divided into four types of insulation: internal insulation, sandwich insulation, integrated insulation and external insulation. The first three due to technical defects, and exterior insulation technology with its reasonable structure, a wide range of applications, eliminate heat bridges, high energy efficiency, thermal stability, increase the use of area, high air tightness, high water The advantages of nature and extending the service life of buildings have become the leading technologies for building energy conservation.

However, there have been many problems in the promotion and application of exterior insulation technology in recent years: insulation board shedding, hollowing, cracking, and indoor condensation. The reasons are mainly the following three aspects: The external insulation technology, the quality and performance of the material do not meet the quality requirements; the external wall insulation design is not perfect; the construction method is not standardized.

1 The specific analysis of the common problems of external insulation of external walls is as follows: 1.1 The reasons for insulation plate falling off are as follows: a. The cement does not meet the technical requirements, the ratio of the cement paste is not proper or the quality and performance do not meet the requirements; the depth of the anchoring of the anchorage is fixed when the machine is fixed. The number of anchorages does not meet the design specifications. b. The grass-roots flatness is not good and no leveling is done. c. The bond area is too small to reach the basic bond area requirement of 30%. d. The density of the benzene board used is insufficient, and the tensile strength is too low to meet the bearing requirements of the insulation system's own weight and surface load on its strength, resulting in damage to the benzene board.

1.2.1 The flatness of the primary wall surface does not meet the design requirements and is not treated. The wall surface is too dry or the water content on the wall surface is too large after rain. The board is affixed without processing, causing slurry dripping, resulting in empty Drums, stickers.

1.2.2 The consistency of glue preparation is too low, and the viscosity index of the adhesive is not reasonable. When the glue is attached to the wall surface, sagging occurs, resulting in the partial paste of the blank on the board surface.

1.2.3 Insulation layer paste method is not correct. The whole board surface is not synchronized to the wall, but one end is overstressed and under pressure. After the board is installed in place, it will be formed due to local rebound of the board surface, and the board surface will be mislaid, empty and empty. .1 The flexibility index of the adhesive can not meet the design requirements, the brittleness is too strong, and the deformation resistance of the screed is insufficient to resist the stress; the content of the organic substance in the adhesive is too high, the anti-aging ability of the mortar is reduced, and cracking occurs for a long time. .

1.3.2 The mixing ratio of cement is too large, the label is too high, and the mortar of the surface layer shrinks too early; the water absorption of the mortar is too high, and the cracking is caused by freeze-thaw and frost heave in winter.

1.3.3 The sand size of engineering sand is too small, the mud content is too high, and the particle size distribution is unreasonable.

1.3.4 The duration of benzene plate is too short (should be greater than 42 days), and the requirements for external insulation maintenance period have not been completed. After the wall has a large post-shrinkage, causing surface cracking; local lining or There is no set cut in the four corners of the window to cause cracking.

1.3.5 The mesh size of the glass fiber mesh cloth is too large or too small, the alkali resistance of the mesh cloth is too low, and the laying method is not standardized (the amount of the grid cloth coating is required to be 20, and the bottom glue should be connected to the mesh cloth Very good compound).

1.3.6 Areas where stress concentration is likely to occur at the periphery of the window, corners, and corners of the wall, and there is no reinforcement mesh to disperse the stress.

1.3.7 Dope is not fully stirred, the surface of insulation board is uneven, especially the adjacent board surface is uneven, resulting in deviation of plaster thickness and inconsistent shrinkage leads to cracks. Gap between boards is not filled with adhesive.

1.3.8 When the steel wire mesh for the surface reinforcement material is used, no crack resistant mortar is used as the surface layer material, and ordinary cement mortar is still used. Cracks occur due to inconsistent linear expansion coefficients of reinforcing steel, cement mortar, benzene board, and cold drawn steel wire.

1.3.9 During the construction of the surface layer under the sun exposure, the surface layer is not timely sprayed and cured to cause shrinkage cracks; when the surface layer is plastered, water is sometimes drowned to make the surface layer aggregates. Too few cracks.

1.3.10 No expansion joints are provided, and the deformation of the system is caused by the stress. In the insulation system, pipelines pass through the wall and materials are not properly treated in the water-repellent treatment or flexible and rigid handling, resulting in cracks.

The causes of the winter surface water condensation: a design scheme is not perfect, there is a thermal bridge phenomenon; b. poor construction quality control, insulation board due to cutting quality or other reasons caused by the gap between the board is too large, did not do insulation board filling deal with.

2 For the common problems that arise, the following suggestions are recommended: 2.1 The external insulation of the building should be the entire external insulation of the entire building. Due to incomplete external insulation, cracks occur in the parapets of the building's parapets, awnings, etc. Therefore, in order to avoid the occurrence of cracks, we should conduct comprehensive insulation of the buildings, including parapets, awnings, and expansion joints. The main reason for external wall insulation cracking is due to the difference in the linear expansion coefficient between the insulation material and the exterior decoration material. The principle of preventing cracks is: by reducing the external insulation material of the building structure with the external decoration, leveling the mortar, the outer surface and other materials The linear expansion coefficient ratio is a gradual layer-by-layer gradient between materials, and flexible release of stress to play a role in preventing cracks.

2.2.1 In the current construction of buildings, the use of heat-insulating materials is mainly based on high-density benzene board, polystyrene board, and polyphenylene granule heat insulation materials. High-density benzene board has the advantages of high density and small thermal conductivity, its thermal conductivity is 0.029W (mK), and the thermal conductivity of crack-resistance mortar is 0.93W (mK). The thermal conductivity of the two materials differs by 32 times. The thermal conductivity of the benzene plate is 0.042W (mK), which is 22 times that of the anti-crack mortar. Therefore, the high-density benzene plate has weaker crack resistance than the polystyrene plate. Polyphenylene granules as the main raw material of the thermal insulation material is made of rubber powder and rubber powder polyphenylene granules, and the powdered powder material is used as the binding material of polyphenylene granules, generally using slaked lime powder - fly ash - silicon powder - cement as the main The composition of the inorganic gelling system, the thermal conductivity of such materials is generally 0.06W (mK), a 16-fold difference compared with cracking mortar. Compared with high-density benzene plates and polyphenylene plates, the thermal conductivity of this kind of material is much smaller, so it can alleviate the accumulation of heat in the anti-crack layer, so that the thermal load and stress caused by the sudden temperature change of the system can be released more effectively. The durability of crack resistance is recommended for more use.

The application of glass fiber mesh cloth as the key reinforcement material of crack protection layer in the exterior wall thermal insulation technology can be rapidly developed. On the one hand, it can effectively increase the tensile strength of the protective layer, and on the other hand, it can effectively disperse the stress. The original cracks can be dispersed into a number of finer cracks, thereby forming a crack resistance. Because the external protective cracking mortar of the insulation layer is alkaline, the long-term alkali resistance of the glass fiber grid cloth has a decisive significance to the cracks. From the durability analysis, the high alkali-resistant fiber mesh cloth has much better durability than the alkali-free mesh cloth and the alkali-base mesh cloth, and can meet the use requirement of at least 25 years. Therefore, in the selection of the enhanced network, It is recommended to use a high alkali-resistant mesh cloth.

The choice of protective layer material is due to the high strength of the cement mortar, large shrinkage, and insufficient flexibility deformation. It directly acts on the outside of the thermal insulation layer, resulting in poor weatherability and cracking. In order to solve this problem, it is necessary to use a special anti-cracking mortar and a reasonable reinforcement net, and add a proper amount of fiber to the mortar so that the cracking ratio of the anti-crack mortar is less than 3. If the exterior facing is a tile, the cement Cracking mortar can also be added to the wire mesh, wire mesh hole spacing should not be too small, should not be passed, the short side of the tile should be covered in at least two holes on the Internet, wire mesh should be used anti-corrosion good hot-dip galvanizing Wire mesh.

2.3 No cavity structure to improve the stability of the system In the design of polystyrene board for external insulation, the insulation layer is mainly subjected to gravity and wind pressure. Due to the limitation of the strength of the polystyrene board, the insulation layer cracks or even falls off. In order to increase the strength of the insulation board, the bonding area should be increased as much as possible to make it free from cavities so as to meet the requirements of wind pressure destruction.

The external wall insulation of buildings is an emerging construction method in recent years. The principle of gradual release and flexible stress release should be selected, materials and construction methods should be selected so as to achieve the purpose of heat preservation and crack resistance. Since the external wall insulation system is an organic whole, the synergy of the various related layers required not only requires a gradual change in flexibility, but also a certain degree of compatibility and synergy to form a composite whole.

To build more and better exterior insulation and energy-saving buildings, it is necessary to work together from the competent departments of the industry to the construction units, design units, construction units, supervision units, and material manufacturers. Strengthen the control of the quality system, follow the external wall thermal insulation technology requirements, formulate a reasonable application technology program, ensure the project quality, in order to promote the application of exterior thermal insulation technology in practice.

Editor: Zhao Shuzhen

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