Common knowledge of coating: analysis and prevention of cracks in plastering of exterior wall of building engineering

Core tips: Information: Building decoration is to protect the main structure of the building, improve the use function of the building and beautify the building In the past, the exterior wall decoration of buildings used mosaic, glazed brick and other building decoration materials, which has been gradually eliminated Now, cement mortar fine brushed plastering is widely used for building external wall decoration, and various high-grade coatings are applied, so as to truly achieve applicability, economy, beauty and generosity However, a large number of cracks are easy to appear in the external wall decoration plastering of buildings, which not only affects the decoration effect of construction projects, but also has a certain impact on the durability of buildings Now combined with teaching research and practical experience, the external wall of buildings Paint knowledge how about Akzo Nobel Powder Coating Recommended introduction: powder coating is a kind of coating with different form from general coating, which is in powder form It is a new type of coating, because of its own advantages and more and more known by people Let's introduce Akzo Nobel Powder coating Akzo Nobel Powder coating is a cost-effective coating solution, which can be applied to different kinds of products After the treatment of static electricity and fire baking, a tough and durable coating surface will be formed, with the least impact on the environment Since the introduction of this technology, powder coating has been able to continue to maintain the Paint Home News: News: architectural decoration is to protect the main structure of the building, improve the use function of the building and beautify the building In the past, the exterior wall decoration of buildings used mosaic, glazed brick and other building decoration materials, which has been gradually eliminated Now, cement mortar fine brushed plastering is widely used for building external wall decoration, and various high-grade coatings are applied, so as to truly achieve applicability, economy, beauty and generosity However, a large number of cracks are easy to appear in the external wall decoration plastering of buildings, which not only affects the decoration effect of construction projects, but also has a certain impact on the durability of buildings Based on the teaching research and practical experience, this paper analyzes the plastering cracks on the exterior wall of the building and discusses the preventive measures 1、 Analysis on the causes of cracks in plastering of building exterior wall decoration The cracks in building decoration plastering are common faults of buildings The common causes of cracks are shrinkage cracks, temperature cracks, hollowing cracks and structural cracks According to the depth of cracks, there are surface cracks, deep-seated cracks and through cracks 1 Shrinkage cracks are the shrinkage or shrinkage of plastering surface caused by the gradual decrease of volume when the cement in the plastering mortar is hydrated and hardened The cement in the mortar has poor stability, and the cement has uneven volume change after hardening, resulting in a large number of shrinkage cracks However, most of the shrinkage cracks in the actual construction are shallow, which are some surface cracks, not for decoration and structure Too much impact 2 Temperature cracks are caused by external constraints when the temperature difference is large or the structure is cooling down Most of the temperature cracks are surface cracks 3 The structural crack is caused by the deformation of the wall structure, which causes the crack of the plastering layer firmly bonded with the structure This kind of crack is relatively obvious, with large length and wide crack width It belongs to the through crack, which is relatively harmful and easy to cause the leakage of the wall It is the key point of prevention and control 4 The hollowing cracks are caused by the weak bonding between the bottom mortar and the wall surface, the insufficient water spraying on the wall surface before construction, and the water quickly absorbed by the wall surface after plastering, which affects the adhesion and forms hollowing cracks In addition, the wall surface is not cleaned, there are floating soil and loose slag left, the mortar construction interval between each layer is too long or too short, the water content of the wall is inconsistent, the mortar mark of the middle layer is higher than that of the bottom layer, and shrinkage stress is generated during condensation, resulting in hollowing of the bottom layer and the wall surface of the middle layer, which may cause cracks in the wall plastering 2、 The part of building exterior wall decoration plastering crack Through the study of several projects, most of the cracks in the external wall decoration plastering of buildings are concentrated in the following parts: 1 The large surface of the wall: especially the large wall without grid joint has a heavier crack phenomenon, because the mortar shrinkage is relatively large I have studied and analyzed more than ten projects, and found that the phenomenon of cracks on the large surface of the wall is very common, and most of the wall plastering has no division joints, or the division joints are set less, or unreasonable 2 Construction joints and screeds: it is inevitable that screeds and construction joints will appear in the plastering construction of exterior wall decoration Due to the different contraction of screeds and construction joints, the contraction cracks are easy to appear due to the difference between the first construction and the second construction In addition, the treatment of these parts fails to meet the requirements, resulting in the occurrence of cracks 3 There are four corners of the door and window opening, especially the two above This phenomenon occurs in more than a dozen projects visited for cracks The main reasons are shrinkage of structural materials, structural deformation, wall settlement and temperature change The shape of the fracture is horizontal and 45 ° obliquely This kind of crack is wide and deep, which belongs to the through joint It mainly occurs in 1 to 2 years after the completion of the project The appearance of these cracks causes the leakage of the external wall There are more leakage phenomena at the two places under the window opening, some of which are serious 4 Joint of parapet wall and roof panel: the plastering cracks on the exterior wall here are mostly horizontal through cracks If they are not treated in time, it is easy to cause wall leakage The cracks on the joint of parapet wall and roof panel are caused by the horizontal thrust of the wall caused by the change of roof panel temperature The other reason is that the structural columns at the parapet wall are not set according to the specification or the spacing is too large 。 5 Decoration line at the structural corner protruding the exterior wall: temperature cracks and dry shrinkage cracks are produced in these parts, which are thin and hard to see, and have no great influence on the structure and the beauty of the building 6 Different materials used in building walls: different materials produce different deformations In building engineering, brick wall and precast concrete column, brick wall and precast concrete lintel, brick wall and precast concrete connecting beam In the project, there are plastering cracks, which will appear soon after plastering 3、 Prevention and treatment of plastering cracks in building exterior wall decoration Many cracks in plastering of building exterior wall decoration can be prevented Some cracks have no great influence on the structure and are allowed However, some cracks have great influence on the structure and are not allowed to appear, which requires the professional technicians to consider the prevention in advance from the aspects of design, construction and maintenance （1） Design: carry out reasonable design in strict accordance with the national design specifications The designer should pay a return visit to the designed project, summarize the experience, and find out the deficiencies and problems in the project, which is very helpful for the future design In the future design, strengthen the structure of the parts prone to cracks, strengthen the tie bars of different materials, and improve the masonry mortar In order to strengthen the integrity of the structure, cast-in-place lintel is set on the opening and cast-in-place slab belt is set under the window （2） Construction mainly from the following aspects of prevention and control: 1 Materials: choose a small dry shrinkage of cement varieties, in the construction of cement inspection, unqualified cement is not used The mud content and impurities of the sand shall be strictly controlled within the specifications, and the thickness of the sand shall meet the requirements The mortar proportion shall meet the design requirements, and the mortar shall be evenly mixed with good workability The mortar that has not been used for a long time in construction, the mortar that has been mixed for more than 3 hours, and the mortar with bleeding phenomenon shall be re mixed before use 2 Wall construction: during masonry construction, the surface shall be flat, overlapped up and down, left and right staggered joints, and the overlapping size shall meet the construction requirements, and no through joints are allowed It should also be noted that the tie bar of the wall should be embedded as required The temporary holes and scaffold holes reserved in the wall shall be sealed tightly and firmly before plastering In some projects, because the foot and hand holes are not blocked firmly, the gap is not filled with mortar when blocking the brick, and some mortar is not plugged in, so that cracks are easy to appear at the foot and hand holes after the wall plastering is dry, and water seepage will occur in the wall when it rains, which is not easy to be found Therefore, we should start from the wall construction, first to ensure the structural strength, so that the structure does not appear deformation 3 Plastering construction: before plastering, the base course shall be cleaned carefully, and the floating soil and loose debris on the wall shall be cleaned Spray water to moisten the wall in advance According to experience, it is better to do it one day in advance The degree of watering is that the wall is basically wet The next day, according to the dry and wet conditions, spray water properly If too little water is sprayed, the water in the mortar will be absorbed by the wall quickly, and the mortar will produce cracks if it shrinks too fast If too much water is sprinkled, it is easy to fall when plastering, which will also lead to cracks Moreover, the watering should be even, and the phenomenon of less wetting and more wetting should be avoided Plastering shall be carried out layer by layer and layer by layer, so as to bond firmly, and can play the role of leveling and quality assurance If the first formwork ash is too thick, due to the different speed of internal and external water collection, it is easy to produce shrinkage cracks According to the design requirements and the overall situation of the wall, adding some grid lines properly can not only increase the three-dimensional sense, but also reduce the occurrence of cracks in the plastering layer When plastering, the joint shall be left at the grid joint or the place where cracks are not easy to appear The joint of plastering shall be treated strictly and smoothly to reduce the occurrence of cracks 4 Strengthen the maintenance: the external wall plastering shall be maintained according to the weather conditions Some constructors on the construction site think that the wall plastering does not need maintenance, which is wrong The external wall plastering shall be maintained according to the weather conditions to prevent some cracks If the plastering is on a cloudy day, the plastering can be watered for maintenance once three days later, and the water can be sprinkled again on the seventh day If it is the second day of summer, it should be watered for curing Home of coatings is specialized in coatings, diatom mud, paint coating, coating technology, fire retardant coating news and coating, diatom mud, paint coating, coating technology, fire retardant coating decoration knowledge and decoration renderings,