As an important building energy-saving technology, external thermal insulation has been highly valued worldwide, and countries have begun to implement practical energy-saving indicators for building walls. Tracing back to the source, this technology originated in Sweden and Germany in the 1940s. It has a history of more than 70 years. After years of practical application and long-term tests in different climatic conditions around the world, it proves the construction of this type of insulation system. Whether it is from the exterior decoration effect of the building or the comfort level of living, it is a new energy-saving technology worthy of promotion and application on a global scale. As a big energy-consuming country, China has gradually implemented three-step energy-saving work steps of energy saving 30%, 50% and 65% since the late 1980s, and has begun to implement the higher energy-saving indicators in conditional cities. Try to prepare conditions for the establishment of the fourth step of energy efficiency indicators. At present, my foreign wall insulation technology has entered a leap-forward development stage. The state has strict legislative work on external wall insulation, including the promulgation of the Minister of Building Energy Conservation, the mandatory requirements for energy conservation in buildings, and the regulation of external walls. The technology and products have been fully utilized for the mandatory standards of the external insulation system and the standards for the relevant constituent materials in the system. But unfortunately, China's research on external thermal insulation has been in a state of insufficiency. Even with rumors, there has always been a lot of misunderstanding in understanding. What's more, some misunderstandings of knowledge have even been written into textbooks, and they have been publicized throughout the country, creating various kinds of fog for external thermal insulation, and also giving their development a mysterious, non-normalized chrome print. As a staff member who has been engaged in research on exterior insulation for many years, the author talks about the basic misunderstandings of these understandings from the perspective of engineering practice, and hopes to cause some thinking. First, the external wall insulation and cracking mechanism: the amount of flexible deformation is layer by layer, layer by layer release stress? In theory, the structural layers of the external thermal insulation system are divided and separated, and each part is placed in the same test environment to establish a unified measure of the amount of flexible deformation. It should be said that “layer-by-layer gradient, The crack-resistance mechanism of releasing stress layer by layer is plausible. However, this premise is not true from the current external insulation system for general applications. First, the external thermal insulation of each structural layer as a composite system of buildings, is a whole internal and external level, it is impossible to split and separate, and it is impossible to accept external impact or natural stress changes in the same environment; As a component of the system, the deformation index is also inconsistent, such as the elastic modulus of the insulation layer, the compression ratio of the plaster, and the flexibility of the flexible putty. Since they are inconsistent, they lack the basis for the same comparison. Therefore, some textbooks have widely publicized a crack-resistance mechanism, which is a conceptual model. It is untenable to carefully scrutinize it. Second, the best choice for the construction of external insulation system: no cavity? The external wall thermal insulation system should preferably use a cavityless system. It is considered that the cavityless system is more resistant to wind pressure, especially negative wind pressure, and has higher safety and reliability than the cavity system. It seems to have reached A consensus is not entirely true. Practice has proved that if the insulation layer uses a material with high water absorption as a bonding material (full adhesion) or a surface leveling material, the quality problems such as moisture, freeze-thaw damage often occur after two to three years. The author was invited by the relevant departments to participate in the quality analysis of some external thermal insulation projects in Xinjiang, Inner Mongolia and Anhui. The residents reported that the insulation effect was not good. After the engineering anatomy, we observed that the above projects are more than two years of engineering, without exception. The materials with higher water absorption rate are used as the full-adhesive material of the polystyrene board and the surface leveling material. The surface of the outer wall is basically free of cracks, but the full-viscosity layer and the leveling layer of the surface are very moist, and the water is outwardly precipitated. After analysis, we believe that the polystyrene board is fully viscous with a high water-absorbent adhesive material. After two to three years, the new building base wall is diffused by water-saturated water vapor, which easily leads to a high-viscosity material with high water absorption. The layer absorbs moisture and moisture; at the same time, when the water vapor migrates from the high temperature side of the room to the low temperature side of the room, if the surface leveling material is a material with high water absorption rate, it is easy to produce condensed water accumulation in the leveling layer of the surface, thereby making the polystyrene board Damp and even mildew on both sides, causing problems such as insulation performance damage. Synchronously researching the above problems, if a slurry material with a high water absorption rate is used as the main heat insulating material, will the same problem be caused by the adsorption of water vapor to the wall and the condensed water that the hot air migrates outward? For further research. Therefore, the polystyrene board adopts the point-frame bonding method, which can effectively prevent the wind pressure from being damaged by the external heat preservation system, and can form the vapor barrier layer, and effectively avoids the polystyrene board being in a damp state for a long time, which is indeed better. select. In this sense, it is not possible to subjectively determine the external thermal insulation of the external wall from the perspective of wind pressure damage. Third, the first factor in the selection of the main material for exterior insulation of the external wall: low thermal conductivity? Because the threshold of the external thermal insulation system technology is not high, the system composition materials and the system itself are often separated and there is a lag in the standard formulation and policy guidance. Some domestic designers have not yet well understood and mastered the external thermal insulation technology. There are still vague concepts for some practices of external thermal insulation. It is often considered that the selection of external thermal insulation materials with low thermal conductivity is a good external thermal insulation system, which leads to the disconnection between design and construction, and the wrong guidance of some enterprises. Wall insulation technology is varied and mixed. From the perspective of architectural mechanics and thermal engineering, external thermal insulation and decoration systems for external external walls of buildings should be considered as composite composite structures, and should not be separated into structural layers, thermal insulation layers, crack resistant layers, and The finish layer was studied separately. Thermal engineering research shows that after the insulation layer is installed, due to the good thermal insulation performance, the thermal insulation layer has different thermal environments inside and outside. Therefore, the research of composite building structure should be based on the boundary of insulation layer. the study. Based on this understanding, we conduct a basic analysis of the selection of external thermal insulation systems. To judge whether an external thermal insulation system is qualified, first of all, it is necessary to calculate whether the thickness of the insulation layer meets the national energy conservation index. Therefore, from the thermal performance point of view, there is no question of choosing which kind of external thermal insulation main material is good or bad. The problem is how the external thermal insulation system meets the ten basic requirements of JGJ144. In general, in the case of meeting the performance requirements of the standard, the construction work should be reasonably organized, and there should be no quality problems in the external insulation of the external wall. At present, the country only introduces the industry standard of two systems of expanded polystyrene board thin plastering exterior wall insulation and rubber powder polystyrene particle insulation slurry, and there are more than ten kinds of external insulation practices in the market, so how to choose External insulation systems are indeed a problem. From years of engineering practice, the author believes that the key to selecting the external thermal insulation system is that the composite building structure has good waterproof and vapor permeability when the performance of various materials in the system can meet the relevant national standards. Generally speaking, the external thermal insulation surface uses polymer special mortar and flexible putty, etc., and its waterproof problem can be solved; but in the problem of vapor transmission, academic and application circles are very controversial. A typical statement is that XPS board Polyurethane and other materials are not vapor-permeable, and are not suitable as the main material for external thermal insulation. In fact, there have been few successful cases in the implementation of engineering. The vapor permeability of the outer wall actually refers to the diffusion ability of water vapor to migrate from the high temperature side to the low temperature side. For the composite building structure, with the insulation layer as the dividing line, the author believes that if the sum of the water vapor permeability resistance of the outer wall and the insulation layer is greater than (and the larger the better) the sum of the surface layer and the decorative layer, in winter At the time, the moisture of the indoor air entering the wall through the diffusion can be smoothly discharged to the outside, otherwise condensation will occur at the junction between the insulation layer and the surface layer, thereby causing freezing and thawing damage. Therefore, for the XPS board, according to the standard, the sum of the water vapor permeability resistance of the insulation layer and the outer wall is greater than the sum of the surface layer and the decorative layer. In theory, it can be used for wall insulation, but the system should be strengthened. Research on constituent materials, especially the study of interface, bonding and smearing materials, should not simply copy the components of the EPS system; but should be cautious about materials such as polyurethane (PU). Fourth, the external wall insulation function: stable main wall? In the practice of engineering, it is often heard that such a discourse "insufficient structural insulation of the external wall", and often the structure is not accepted or the acceptance is unqualified, the phenomenon of external thermal insulation is directly done, and the structural engineering has a large hidden danger; In the case of external thermal insulation, from the perspective of economic effects, the structure is often not leveled and corrected according to the requirements of the specification, which brings many safety hazards to the quality of the external thermal insulation. It is really “outside the light, there is a bag insideâ€, the quality is worrying. . The so-called external insulation of the outer wall refers to the construction of an insulation layer on the outer surface of the vertical outer wall. The author believes that the function of the outer insulation layer is limited to increase the insulation efficiency of the external wall and the related requirements, and it should not be expected that the insulation structure of this layer will play a role in the stability of the main wall; the main wall, ie the outer insulation layer The base must meet the requirements of the mechanical stability of the building, can withstand vertical loads, wind loads, and can withstand impact and can be used safely. It should also be able to firmly fix the insulation layer and the decoration layer covering the surface. Of course, for the external thermal insulation system, there are still many misunderstandings in the composition of materials, system design, construction applications, experimental research, etc. These four basic misunderstandings directly affect the in-depth and development of external thermal insulation technology. Caused enough attention. In the specific research and operation of the external thermal insulation system, there is also a problem of corporate conscience and social responsibility. At the same time, the government should actively take effective measures to correctly guide the direction of external thermal insulation development, and effectively break the current external thermal insulation market. , the owner sees the price, the general package to see the rebate, the supervision to see the red envelope, the hidden rules and the rules of the game. 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