Interpretation of Four Fundamental Misunderstandings in Outer Wall External Thermal Insulation
Firstly, the anti-cracking mechanism of exterior insulation of exterior wall: flexible deion changes abruptly layer by layer and releases stress layer by layer?
In fact, the crack resistance mechanism of "layer by layer mutation, layer by layer release stress" can be said to be feasible by dividing the structural layers of external wall thermal insulation system and putting each part of it in the same experimental environment and setting up a consistent trade-off goal of flexibility deion. However, as far as the exterior insulation of exterior wall is fragmentary, this premise is not valid. Firstly, as the composite fragments of buildings, each structural layer of external wall thermal insulation can not be split and separated, nor can it withstand the impact of external forces or various stress changes in nature under the same environment; secondly, as the fragmentary constituent data, its deion objectives are not divergent, such as the elastic modulus of thermal insulation layer, the compression-flexibility ratio of plastering mortar, and softness. Flexible deion of sex putty, etc. Since there are no differences, there is no basis for the same analogy. Therefore, the current textbooks generally preach the anti-cracking mechanism, which is actually a conceptual model, and careful consideration is untenable.
Second, the best choice of exterior insulation fragmentary structure: no cavity?
External wall insulation system should give priority to non-cavity fragmentation. It is believed that the anti-wind pressure, especially the negative wind pressure, is stronger and safer than that with cavity fragmentation. It seems that a consensus has been reached, but it is not the same in reality.
Third, the first factor for selecting the main material of external wall thermal insulation: low thermal conductivity?
Because of the low threshold of the fragmentary technology of exterior wall thermal insulation, fragmentary composition data and fragments are often separated and lagged behind in the formulation of standards and policy guidance. International local designers have not yet had a good view and mastery of the technology of exterior thermal insulation, and some practices of exterior thermal insulation still have vague concepts, often assuming that the main material of exterior thermal insulation with low thermal conductivity should be selected. That is, good external wall insulation is fragmentary, which leads to design and construction disconnection, and incorrect guidance of some enterprises, which also makes the external wall insulation technology varied and uneven.
Generally speaking, the waterproofing performance of exterior insulation can be lost if polymer mortar and flexible putty are used for exterior insulation. However, there is a great controversy in the academic circles and the use circles on the performance of steam permeability. A typical analogy is that the data of XPS board and polyurethane are not vapor permeable, and they are not suitable as the main material of exterior insulation. In reality, there are few successful cases in the project.
4. External wall thermal insulation function: fluctuating main wall?
In engineering theory, we often hear such words as "structure lacks external wall insulation supplement", and often present the situation that the structure does not accept or fail to pass the acceptance test, so it indirectly does external wall insulation, and the hidden danger of the construction project is bigger. When indirectly doing external insulation, we often think about the economic effect and rectify the structure according to the standard requirements first, which also brings a lot of flatness to the quality of external insulation. The hidden danger is "slipping away inside, a bag of chaff outside", the quality is worrying.
The so-called external wall thermal insulation refers to the construction of thermal insulation layer on the surface of vertical external wall. In my opinion, the function of external thermal insulation layer is limited to adding external wall thermal insulation efficiency and related requirements, and should not expect this thermal insulation structure to play a role in the fluctuation of the main wall; the main wall, that is, the base of the external thermal insulation layer, must meet the requirements of the fluctuation of building mechanics, can accept vertical load, wind load, and can be used safely against impact. It should be able to make the insulation and decoration layers on its surface firm.
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