Problems that arise after construction of ready-mixed plastering gypsum mortar

Remarkable progress has been made since the application of ready-mixed gypsum mortar in construction projects. Ready-mixed gypsum mortar is gradually being accepted and adopted by the construction industry in construction projects in our city. There have also been some quality problems and controversies in the engineering application of ready-mixed gypsum mortar, mainly in plastering gypsum mortar, especially concrete shear wall plastering gypsum mortar, which has the most problems; ready-mixed gypsum mortar as a There must be a process for new materials to be familiarized and mastered by people; now we will discuss the common problems in the construction of ready-mixed plastering gypsum mortar with everyone, in order to solve the problems and promote the promotion and application of ready-mixed gypsum mortar.

1. Changes in construction requirements brought about by ready-mixed plastering gypsum mortar

(1) Increase the requirements for the ability of plastering construction workers to adapt to changes in the properties of gypsum mortar. When preparing gypsum mortar on site, the construction workers feel that the gypsum mortar has poor workability. They can change the gypsum mortar formula or strengthen mixing to make the workability of the gypsum mortar conform to the workers' construction habits. For example, if you feel that the gypsum mortar is a little sticky, you can adjust it by adding more gypsum mortar plasticizer or stirring for a longer time; if you find that the viscosity is not good and there is a lot of material falling off, you can solve the problem by adding a little more cement. After long-term use of on-site preparation of gypsum mortar, construction workers have mastered a set of skilled processing techniques and construction habits; this is to meet the construction workers' construction habits by changing the properties of gypsum mortar at the construction site. The advantage of this method is that adjusting the gypsum mortar is fast, simple and highly targeted; the disadvantage is that the gypsum mortar formula will be changed at will, and the quality of the gypsum mortar will fluctuate greatly, which may cause the quality of the gypsum mortar to fail to meet the requirements of the project, and the project quality will not be improved. Effective protection. After using ready-mixed gypsum mortar, the gypsum mortar is prepared in the factory. It is impossible to change the performance of the gypsum mortar by adjusting the gypsum mortar formula at the construction site. This requires the construction personnel to have high plastering skills and change their working methods. To adapt to the performance changes of gypsum mortar, and operate in strict accordance with the construction regulations to ensure construction quality.

(2) After using ready-mixed plastering gypsum mortar, the strength of the gypsum mortar is increased. After the strength of the gypsum mortar plastering layer is increased, the plastering process is affected. The interface treatment with the plastering matrix brings some new changes. The use of low-strength gypsum mortar can improve plastering efficiency and reduce hollowing and cracking of the plaster layer. Since there are no quality requirements for the strength of plastering gypsum mortar in relevant standards, low-strength plastering gypsum mortar is often prepared when preparing gypsum mortar on site for construction. The strength of the plastering gypsum mortar in a considerable number of projects does not meet the requirements of the plastering project. The gray layer is full of powder when touched and falls off when picked. The quality of the gypsum mortar plastering project cannot meet the decoration requirements. This situation is especially obvious when the strength of gypsum mortar increases slowly in winter. Customers complain that many ready-mixed plastering gypsum mortars are harmful to gypsum mortar. The strength is specified and the strength of ready-mixed plastering gypsum mortar is supplied to gypsum mortar. After the strength of plastering gypsum mortar is increased, the stiffness of the gypsum mortar plastering layer increases, and the tensile stress of the gypsum mortar plastering layer on the plastering interface treatment layer increases. The quality of plastering base surface treatment must be improved accordingly, and the plastering construction regulations must be strictly followed. Require construction to ensure construction quality.

2. Analysis of common problems and causes in the construction of ready-mixed plastering gypsum mortar

(1) The foundation wall is uneven and has not been leveled, resulting in cracking and hollowing of the plaster layer. The thickness of the gypsum mortar layer applied at the same time is uneven, because the thick parts dry slowly and the thin parts dry quickly; when the gypsum mortar dries, it is accompanied by the hardening and shrinkage of the gypsum mortar layer. The parts of the gypsum mortar that dry quickly harden and shrink early. The slow-drying gypsum mortar parts harden and shrink slowly, which forms internal stress inside the gypsum mortar layer; when the thickness deviation of the plastering gypsum mortar layer is large, this inconsistent deformation may lead to structural damage, hollowing or cracking. . When parts are thicker and most parts are thinner, especially when the thickness gradient is steeper, local shrinkage cracks are prone to occur; when parts are thinner and most parts are thicker, especially at the edges of door and window openings or at the corners of walls, while gypsum When the bonding strength between the mortar layer and the base material is weak, the gypsum mortar layer and the base layer often pull apart, resulting in hollowing. Therefore, when the plastering base surface is uneven, the plastering base surface should be leveled. After leveling, let it cool for 5 to 7 days before applying plastering gypsum mortar.

(2) The fall of the gypsum mortar plastering layer causes cracks. If the gypsum mortar plaster layer does not thicken and loses fluidity for a long time, the gypsum mortar plaster layer may fall and slip under its own gravity, resulting in cracking of the gypsum mortar plaster layer. This situation mainly occurs when the plastering base surface has low water absorption, the thickness of the plastering is too thick at one time, or the gypsum mortar is soaked by rain before it solidifies after plastering; this phenomenon is easy to occur in winter when the temperature is low. To avoid this situation, firstly, we must strictly follow the construction technical regulations, which require that the thickness of the gypsum mortar plastering should not be too thick at one time. When using multiple layers of plastering, the time interval between each layer of gypsum mortar plastering must be sufficient. Do not plaster, and appropriately reduce the water consumption of gypsum mortar to prevent damage immediately after plastering.It is recommended to increase ventilation after plastering when the temperature is low in winter.

(3) The rapid loss of water in the gypsum mortar plastering layer causes cracking. During the thickening, drying, condensation and solidification process of the gypsum mortar plastering layer, the gypsum mortar shrinks. The shrinkage that occurs when gypsum mortar is thickened and dried is called the early shrinkage of gypsum mortar. The shrinkage that occurs when the gypsum mortar is further hydrated and enhanced after solidification is called the later shrinkage of gypsum mortar. The early shrinkage of gypsum mortar is much greater than the later shrinkage. Generally, the early shrinkage of gypsum mortar is The value is around 1%. Generally, the shrinkage value of masonry walls is within three thousandths, and is mainly concentrated at the mortar joints of the masonry. The shrinkage value of concrete walls is about five thousandths. The shrinkage difference between the plastering gypsum mortar layer and the plastering base material Generally, the rigidity of the plastering matrix is ​​much greater than that of the gypsum mortar plastering layer. This shrinkage difference can easily lead to cracking of the gypsum mortar plastering layer. This is one of the main reasons why the building gypsum mortar plastering layer cannot completely avoid cracking. The faster the gypsum mortar plaster layer loses water and dries, the more violent it will shrink and the more likely it is to crack.

This situation often occurs in summer when the temperature is high or the wind speed is high. The plastering construction time in summer should be adjusted to strengthen the protection of the gypsum mortar plastering layer and avoid direct sunlight, thereby preventing the gypsum mortar plastering layer from cracking due to rapid water loss.

(4) The different water absorption rates of the plastering base materials cause the gypsum mortar plastering layer to crack. Due to the different water absorption rates of the plastering base materials of the gypsum mortar plastering layer, the gypsum mortar thickens and hardens at different speeds and shrinks at different speeds. Cracks are prone to occur at the junction of the two plastering base materials. For example, at the junction of masonry walls and concrete beams and columns, since the water absorption rate of concrete is much lower than that of shale fired bricks or aerated concrete blocks, cracking is often prone to occur in these places. To avoid this phenomenon, the main construction treatment measures are to lay a layer of steel wire mesh or fiberglass mesh overlapping at the junction of different base materials, first apply a thin layer of gypsum mortar, and then perform gypsum mortar plastering construction.

(5) Cracks in the gypsum mortar plaster layer caused by structural changes in the plaster matrix. When gypsum mortar shrinks, due to different constraints, it is divided into free shrinkage and restricted shrinkage. The free shrinkage value of gypsum mortar is larger than the restricted shrinkage value. When the restrictive conditions are sufficient, the gypsum mortar components may not shrink; this is in gypsum mortar. Adding fiber or laying steel mesh in the plaster screed can reduce or avoid the causes of plaster screed cracking. The inner surface of the plastering gypsum mortar layer on the surface of the plastering matrix, which is bonded to the base surface, is restricted by the surface of the matrix. When it shrinks, the matrix is ​​pulled outward to prevent it from shrinking, and its shrinkage value is smaller than that of air. The outer surface of the gypsum mortar plaster layer in contact is small. Due to changes in the structure of the plastering matrix, the matrix constrains the deformation of the gypsum mortar inconsistently, resulting in inconsistent shrinkage in different parts of the gypsum mortar plastering layer. For example, door and window openings have three-way constraints on their edges and four-way constraints on the middle parts. Walls, beams and columns The same is true at corners; because these locations are prone to cracking due to the difference in deformation of the gypsum mortar plastering layer in different parts; therefore, a layer of steel mesh or fiberglass mesh should be added to the gypsum mortar plastering layer around the door and window openings to prevent the gypsum mortar from cracking. The plaster layer is cracked.

(6) The interface treatment layer is not strong enough, resulting in hollowing and peeling of the gypsum mortar plastering layer. When the surface of the substrate is relatively smooth and the plastering gypsum mortar is not easy to bond, in order to ensure that the plastering gypsum mortar and the substrate are firmly bonded, the surface of the substrate needs to be roughened. This layer of material is called the interface treatment layer. After the gypsum mortar solidifies, the cement in the gypsum mortar continues to hydrate and harden. This process is accompanied by the shrinkage of the gypsum mortar. The later shrinkage of the plastering layer of gypsum mortar forms a tensile stress in the interface treatment layer of the plastering matrix. The thickness of the plastering layer is about 100%, and the greater the tensile stress on the interface treatment layer. The higher the strength of the gypsum mortar in the plastering layer, the greater the tensile stress on the interface treatment layer. Larger; the finer the plaster layer gypsum mortar sand, the greater the tensile stress on the interface layer. When the bonding strength between the interface treatment layer and the base surface is insufficient, or the strength of the interface treatment layer is low, the later shrinkage of the gypsum mortar plastering layer may cause the interface treatment layer to separate from the base surface, or the plastering layer gypsum mortar may pull the interface treatment layer , the gypsum mortar plastering layer and the matrix have hollowed out and peeled off. When this happens, there is often no problem in the early stage. Generally, after half a month, as time goes by, the hollowing of the gypsum mortar plaster layer becomes more and more serious. To avoid this situation, firstly, the bonding strength between the interface treatment layer and the matrix and its own strength should be improved to ensure a strong bond with the matrix; secondly, the thickness of plastering with gypsum mortar should not be too thick in one go. It is prohibited to apply it in one go. Appropriate time intervals should be maintained between layers of plastering; for plastering thickness exceeding 20mm, multiple plastering processes should be adopted.

Ready-mixed gypsum mortar is a new type of material, and there is a process of constant familiarity and mastery during use. After using ready-mixed plastering gypsum mortar, more stringent requirements are put forward for the quality of concrete interface treatment, the thickness of each gypsum mortar plastering; and when the thickness of the gypsum mortar plastering layer is too thick, multiple plastering processes should be used, which puts forward more stringent requirements. Many problems currently occurring in construction can be avoided if the current gypsum mortar construction operation process is strictly followed.

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