Analysis on the causes and control measures of building external wall leakage?

The following is the related contents about the causes and control measures of building external wall leakage brought by Zhong Da Consulting for your reference.

Wall cracks are one of the common housing quality problems. The appearance of house cracks will affect the beauty of the house, seriously affect the structural bearing capacity of the whole house and even lead to the collapse of the house. Wall cracks have become a common quality problem in buildings, which seriously affects people's quality of life-not only affecting aesthetics, but also easily causing security risks. Therefore, it has become the focus of attention to study the causes of wall cracks and then take corresponding control measures. It is from this point of view that literature and case analysis are used for relevant analysis.

External wall leakage is a common phenomenon in construction, and it is also one of the main quality defects in construction. The leakage of buildings will affect people's normal life, cause property losses and mental burdens, and also bring trouble to property management and professional maintenance.

1 Cause analysis of external wall leakage

1. 1 The leakage of frame infilled wall mainly occurs at the junction of infilled wall and frame beam and column, especially at the contact between the bottom of roof beam and the top surface of brick wall masonry, which is the frequent part of cracks and leakage. This is because the linear expansion coefficient of concrete and brick masonry is different, and the linear expansion coefficient of concrete is about twice that of brick masonry. At the same temperature, due to the different deformation values of concrete and brick masonry, cracks will occur in adjacent parts, so rainwater will penetrate into the house along the cracks under the action of wind pressure. However, the temperature deformation difference between the top reinforced concrete roof and the adjacent wall is large, and the bottom of the roof beam is not connected with the brick masonry, which is not easy to fill. Under the constant action of external temperature change, humidity change, masonry shrinkage and other factors, cracks are easy to appear and seepage channels are formed.

1.2 workers did not strictly follow the construction specifications in masonry construction, and the masonry mortar was not full, especially the vertical mortar was not full, which even caused the joints to be too tight and straight. In addition, when the dry brick is on the wall, the moisture in the mortar is absorbed by the brick, which leads to the low mortar strength and the separation between the brick and the mortar, which reduces the overall stiffness of the masonry and causes the mortar joint to crack, and water can easily penetrate from the cracks between the bricks, which is also one of the reasons for the leakage of the external wall.

1.3 The cracks in the external wall caused by various reasons make rainwater directly penetrate into the room from the cracks, which is also an important reason for water seepage. Cracks may be caused by structural deformation or temperature stress and strain. Especially in the window, under the top wall window and at the contact interface of different structural materials, such as weak parts such as wall and beam bottom, wall and column edge. , is the focus that we should pay attention to.

1.4 the one-time or local undercoat of exterior wall decoration is too thick to ensure the full verticality, and cracks are generated at the undercoat without taking appropriate strengthening measures; The surface of the structural layer is too smooth, and if no measures are taken, the base will be empty, cracked and poorly combined; The exterior wall is primed in a large area, and there is no frame line at the grass-roots level, which causes irregular shrinkage cracks at the grass-roots level. All the above reasons may lead to the poor quality of the base, which directly affects the combination of the surface layer and the structural layer, thus causing quality problems such as hollowing, cracking, segregation and falling off between the surface layer and the base.

1.5 A large number of facts show that buildings with brick as decorative surface are more prone to leakage than buildings with other decorative surface. After detailed observation, research and analysis, it is mainly due to the hollow tile paving or insufficient mortar paving, resulting in the partial separation of tile and mortar, and the gap between tile and mortar is easy to form a water storage container; Brick jointing is not dense or cracked, and the omission of jointing is the cause of rainwater infiltration from the surface, resulting in water leakage.

1.6 During the surface construction of horizontal members such as window sill, sun visor and awning, the slope can not be found, or even reversed, resulting in backwater or water accumulation, which is also easy to cause water seepage on the external wall. Construction joints are left at parapets (especially brick parapets). Due to the large temperature difference of the roof, the parapet and the roof panel have different rates of thermal expansion and contraction, and there are inevitably micro-cracks at the parapet. Roof rainwater flows to the downpipe along the slope direction of the parapet, which will cause parapet leakage and affect the beauty and quality of the building.

1.7 The leakage of cracks in plastering layer and tile of external wall is mainly due to the large silt content and fine particles of sand used in plastering mortar. Too much water or incorrect admixture content during construction mixing increases the porosity of mortar, which not only reduces the bonding strength between plastering mortar and wall, but also easily causes a large number of dry shrinkage cracks in plastering layer. Due to the poor quality of masonry, the thickness of plastering layer of external wall is too thick, which leads to cracking, shelling and falling off. It can be seen that the external wall plastering leakage is mainly caused by the preparation of plastering mortar, plastering operation and structural quality. At the same time, there is leakage at the joints of exterior wall tiles, which is generally due to careless construction of decoration projects, different sizes, insufficient and dense caulking cement slurry, and too thin cement slurry for the bonding layer that has not been constructed according to the requirements of specifications. So that the materials used can't play their due waterproof role.

1.8 leakage around aluminum alloy plastic steel window frame of external wall; The leakage of the window frame of the external wall is mainly concentrated at the top of the window frame, the window sill and both sides of the window frame bordering the external wall, especially the window sill. The spray test shows that the rain from the outer wall seeps into the room due to the crack between the window frame and the plastering layer of the outer wall.

1.9 Leakage caused by water supply and drainage pipeline installation; When UPVC is installed, construction workers usually only pay attention to the tightness of pipe joints, the firmness after installation and the overall effect of appearance, but pay insufficient attention to the repair of holes where pipes enter indoor and through walls through external walls.

2 External wall leakage control measures

2. 1 Attention must be paid to the waterproof design of external walls. At present, the content of exterior wall waterproofing in engineering design and construction drawings is almost blank, and there is no detailed drawing of exterior wall waterproofing structure and construction instructions in the whole design drawings, which makes the construction unit at a loss. Ignoring exterior wall waterproof design is a common problem in residential engineering design. From the beginning of design, various measures are taken to improve the foundation stiffness and overall stiffness of the building. As for the building measures, the plane of the building should be concise and regular, try to avoid complex modeling and excessive internal angle, and avoid obvious height difference and load difference in the building. Structural measures to control the aspect ratio of buildings. The length-width ratio is the main factor to ensure the stiffness of brick-concrete structure buildings. Buildings with high aspect ratio have poor adjustment ability to uneven deformation of foundation. On the contrary, if the length-height ratio of the building is controlled within a certain range, it has the ability to adjust the uneven deformation of the foundation. Practice has proved that the length-width ratio of buildings should be controlled between 2.5 and 3, which can reduce the relative bending of buildings and generally prevent cracks. Foundation and foundation reinforcement measures, building foundation design must focus on controlling deformation value. The design unit must check the final settlement and eccentricity of the foundation. When the building has complex shape and poor longitudinal stiffness, the final settlement of foundation in soft soil area must be controlled within 150mm, and the eccentricity should be controlled within 15%.

2.2 Starting from strengthening the construction process and management, the construction quality can be effectively improved. The quality of masonry engineering is mainly reflected in whether the strength and integrity of masonry meet the design requirements and whether the appearance is flat, tidy and beautiful. The strength, integrity and appearance of masonry depend on the quality of masonry materials and the quality of masonry technology. Masonry engineering is a comprehensive construction process, and its construction quality is one of the important guarantee conditions to prevent wall cracking. Construction technicians shall make technical disclosure to the workers, and strengthen spot check and re-inspection. It is forbidden to put dry bricks on the wall, strictly control the mortar mixture ratio, ensure that the mortar is full and the horizontal joints are covered with mortar, and at the same time, adopt extrusion and other methods to ensure it. Where the vertical joints are not full, mortar can be carefully filled with a hook trowel to ensure it (this method requires double-sided operation in the external wall, which is often ignored by the construction unit because of the trouble and difficulty in the inspection of the external wall construction, causing hidden dangers). At the same time, it should be noted that the mortar joint on the inclined roof of the external wall should be checked again on the external wall operating frame three days before plastering. If it is not hooked or cracked, it should be filled, and the width of the sinking crack should be kicked out not less than10 mm.

2.3 For the wall seepage caused by various cracks, the solution is to thoroughly find out the root causes of cracks and solve them, and at the same time take preventive and reinforcement measures for the parts prone to cracks. For example, wall cracks are caused by uneven settlement of foundation or structural deformation, so the design unit should be invited to cooperate with the reinforcement scheme to solve the foundation or structural problems first and then repair the wall cracks. For example, the top floor is greatly affected by the temperature change, and the contact interface between the wall and different building materials such as beam bottom and column edge is cracked due to different temperatures and strains. First, the cracked sub-floor is chiseled off, steel wire mesh is added, then layered compaction is carried out with high-grade cement mortar, and maintenance is paid attention to, and then surface construction is carried out, which can effectively prevent cracks and achieve the purpose of reducing wall leakage.

2.4 For the leakage caused by cracks at the grass-roots level, which affects the surface quality, it is considered that it is mainly to strengthen the quality management of grass-roots construction and take effective measures. First of all, it is necessary to ensure that the exterior wall primer is not too thick, and the parts that are too thick should be reinforced with shotcrete or steel wire mesh (especially those parts that require special shapes in architectural design). Secondly, the exterior wall primer should be graded and layered to prevent the primer from being exposed to the sun or rain before the final set, and to strengthen the maintenance. Do a good job of dividing lines, especially for exterior walls such as tiles and mosaics with no dividing lines on the decorative surface. The dividing line should also be kept in an appropriate position, and the upper layer should be coated after the joints are filled with ointment. Thirdly, for smooth structural layers such as concrete columns and beams, it is advisable to use 10% dilute hydrochloric acid solution to wash away the oil stain and isolation agent on the surface layer, then rinse it with clear water, and then "roughen" it with polymer mortar (the mixture ratio of polymer mortar can be 107 glue: water: cement: sand =1)

2.5 For the building with external wall facing brick, technical disclosure must be made in advance before external wall construction, and at the same time, workers' quality awareness and sense of responsibility should be strengthened. In the process of paving, there must be a squeezing process. Before jointing, we should comprehensively check the empty drum to ensure the compactness of jointing. After jointing, we should pay attention to wet curing and do not miss the joints. It is suggested that the depth of jointing should be strictly controlled, the concavity should not be too large, and it is best to hook it into a circular flat seam. Quality management should establish a multi-level review control system to ensure the quality of each process. At present, it is suggested to give priority to a new type of polymer bonding material and use beneficial cement instead of traditional cement as the bonding material for plates. The beneficial cement has the advantages of small dosage, thin thickness and simple construction technology, and avoids the hidden danger of empty drum and falling off caused by insufficient brick soaking and sprinkling. In particular, this beneficial adhesive has other characteristics-high bonding strength when used as an interfacial agent, it can be used on a smooth base surface without coarsening, and it has waterproof performance. When in use, a thin layer (only 1.5~2mm) is fully coated on the base surface of the external wall. Even if some surface layers are empty or the jointing quality is not ideal, there is an extra barrier to prevent rainwater from infiltrating into the base surface of the external wall.

2.6 horizontal components such as window sills, sun visors and awnings shall be aligned as required, and the contact parts with the wall surface shall be treated as flashing arc angles. The periphery of the window frame should be sharp and sticky, the fortress behind the window should be tight, and the top of the window should be eagle-billed. During roof construction, special attention should be paid to pouring more concrete 10~ 15mm at the parapet root than at the roof concrete to ensure that the construction joint at the parapet root is higher than the roof panel, and then the parapet is laid, so that even if there are tiny cracks at the construction joint, it will not cause water seepage at the parapet root and ensure the beauty of the building.

2.7 It is recommended to use three rows of porous or other light solid blocks for external wall masonry. When hollow bricks or perforated bricks are used to build external walls, in order to improve the waterproof ability of masonry, bricks with complete edges and corners should be selected outside the bricks. When the wall length is inconsistent with the brick modulus, the insufficient modulus will be adjusted by solid brick or plain concrete. After the completion of external wall masonry, we should try to avoid chiseling. If there are embedded concealed pipes, seams can be left on both sides of the installation pipeline position in advance when laying, and Rachel steel bars are left vertically every 600mm between seams, and Rachel steel bars extend into the wall for 250mm, and C20 fine stone concrete is poured after laying. At the same time, the wall defects caused by scaffolding holes and cable holes should be repaired before plastering, leaving no hidden dangers.

2.8 Strictly control the construction quality of external walls. In order to ensure the quality of external wall masonry, the quality and strength grade of masonry bricks and mortar must meet the design requirements. Masonry (above the foundation) should generally use mixed mortar. Before bricklaying, the brick should be watered and wetted one day in advance to make the moisture content of the brick reach about 20%. The thickness and fullness of mortar joint and the verticality and flatness of the wall should meet the specification requirements when building the wall. Frame-filled wall brick masonry must be equipped with Rachel reinforcement according to the design and construction requirements, and the contact between the bottom of the frame beam and the top surface of the brick wall should be closed with inclined bricks after the natural settlement and stability of the wall (not less than one week).

2.9 Anti-seepage treatment around aluminum alloy plastic steel window frame of external wall. Loose materials (such as mineral cotton sliver and glass fiber cotton sliver). ) or chemical foaming agent are layered and tightly sealed around aluminum alloy and plastic steel window frames. When plastering the external wall, a notch with a depth of 5mm and a width of 5~8mm must be reserved outside the humanly scaled opening to ensure the cohesiveness and sealing performance of the sealant. The groove base filled with sealing material must be dry and clean, and the sealant should be evenly filled in the groove, with no cracks and pores on the surface.

2. 10 Anti-leakage treatment of exterior wall details, including repair of water supply and drainage pipe through-wall holes, waterproof sealing treatment of exterior wall riser fixing place, etc.

2. 1 1 It is suggested to spray waterproofing agent on the external wall for waterproofing.

2. 12 Strengthening the protection of building external walls. In order to prevent external wall leakage caused by interior decoration of new buildings, when the project is delivered, the building management department should be advised in writing to formulate necessary preventive measures to standardize the owner's decoration behavior.

Concluding remarks

To sum up, leakage is a common quality problem and a chronic disease, but it is not inevitable. As long as we can pay enough attention to this common problem, carefully construct according to the requirements of the code, treat every link seriously, and actively adopt advanced and scientific construction technology and new materials, the leakage problem can be effectively controlled, so that people can live in safe, beautiful and reliable housing.

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