What are the causes of wet stains on the external walls of buildings and how to prevent them?

It is precisely because of unreasonable design, improper material selection, nonstandard construction technology, careless handling of details, improper use or maintenance by users and natural environmental conditions that the external wall surface is easy to fall off and empty, and the indoor wall surface is moldy and peeling, which not only affects the beauty and normal use of the building, but also affects the service life of the building. Synthetic polymer decorative materials with strong impermeability and certain elasticity should be selected to enhance the impermeability of the wall.

1. 1 Leakage of external wall concrete members and reinforced concrete frame filler wall.

1. 1. 1 The water-cement ratio of shear wall concrete is too large, which leads to a large number of bubbles in the process of concrete vibrating, which is not dense, resulting in honeycomb, cavity, rotten roots and shrinkage cracks. The seepage of shear wall external wall is mostly caused by the lax sealing of bolt holes in formwork wall after construction. In the process of concrete pouring, the shear wall will use opposite bolts to ensure the section size of the component and make the template have sufficient rigidity. In order to save materials and engineering costs, plastic pipes are often added to the through-wall bolts, and the bolts are removed and pulled out for recycling, so that the concrete members will leave threaded holes running through the inside and outside.

1. 1.2 The quality of masonry engineering is poor. The strength grade of masonry mortar is low, and the mortar category is improperly used. For example, the external wall is built with lime mortar or mixed mortar with poor mixture ratio, which reduces the strength, makes the masonry integrity poor, and is prone to premature weathering and brittle cracking; Building a wall with dry bricks leads to poor bonding between mortar and dry bricks; Incorrect masonry method leads to mortar plumpness less than 80% in horizontal mortar joint of brick layer, and there is no mortar in vertical mortar joint (empty joint or blind joint), which reserves an internal channel for rainwater leakage.

In the frame structure of 1. 1.3, when the infilled wall is built near the bottom of beam or slab, it is not operated according to the specification requirements. When the masonry is built to the top at one time, the masonry has certain deformation and horizontal cracks appear at the joints. Moreover, there is no reinforced connection between the bottom of the roof beam and the masonry, which is not easy to fill. Under the constant action of external temperature change, masonry shrinkage and other factors, cracks are easy to appear and water seepage channels are formed.

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1.2 reserved holes and embedded pipe fittings on the external wall lead to leakage.

1.2. 1 reserved holes (such as scaffolding holes, pipeline holes during water and electricity installation, equipment materials, pedestrian entrances and exits, etc.). ) failed to fill in the post-repair, forming a leakage channel.

1.2.2 The embedded pipe fittings are not installed firmly, or the embedded parts are drilled and installed after the exterior wall decoration, or the embedded pipe fittings are impacted during construction, and the old and new mortar are not well combined, resulting in empty drums and cracks, and some embedded parts are not filled after installation, resulting in water seepage.

1.3 leakage caused by defects in decorative surface of external wall

At present, it is more and more common to use decorative layers on exterior walls. There are mainly two kinds of decorative materials: one is plastering cement mortar, the other is plastering exterior wall paint; The second is to lay all kinds of tiles, such as tiles, tiles, glass tiles, marble, granite and so on.

1.3. 1 grassroots is not cleaned; The mix proportion of mortar is not allowed, the consistency control is not good, the sand used for plastering mortar has large silt content and fine particles, too much water for construction mixing or incorrect dosage of additives, which increases the porosity of mortar, not only reduces the bonding strength between plastering mortar and wall, but also easily causes a large number of drying shrinkage cracks in plastering layer.

1.3.2 Due to the poor quality of masonry, the thickness of plastering layer on the external wall is too thick, and it is not layered according to the specifications during construction or the plastering on the back layer is too tight; Surface plastering at the junction of different matrix materials did not take anti-cracking measures, resulting in cracking, hollowing and falling off. Improper construction technology of mortar external painting, too wet or too dry grass-roots treatment, insufficient watering or too much watering will all cause the surface layer to fall off or dry up, forming a hidden danger of leakage.

1.3.3 Irregular shrinkage cracks are caused by too deep embedding of frame strips, which destroys the integrity of the outer powder bottom layer or improper operation of embedding wood strips during construction, resulting in uneven thickness or even breakage of the subbase, or large-area plastering of external walls without frame lines.

1.3.4 The plastering area is large, and there are many construction joints, which are greatly influenced by the climate and are prone to cracks and hollowing. On the same construction surface, using several kinds of mortar with different mixing ratios causes different shrinkage cracking and hollowing. The quality of wall coating is unqualified, the film thickness is not enough, the ability to adapt to the deformation of the base is poor, and it is easy to fall off after aging and lose its waterproof effect.

1.3.5 The soaking time of facing blocks is not enough, which leads to dehydration in the early stage of mortar or not drying after soaking, and slipping after pasting. Due to the heavy weight of exterior wall veneer, large deviation of base surface, improper treatment or construction operation at the grass-roots level and poor bonding strength between layers, the surface layer is empty and even falls off from the building.

1.3.6 If the tile is empty or the mortar is not full, the gap between the tile and the mortar is easy to form a water storage bag; The jointing mortar is low in label, sloppy in jointing, insufficient in thickness, full and unsmooth, which slows down the rainwater flow, increases the water retention time and quantity, and seeps into the room through capillary holes under pressure.

1.4 Leakage caused by improper deformation joint structure

1.4. 1 The deformation joint is improperly set or not treated as required, and there are inclusions in the joint that do not penetrate, forming a rigid structure, which changes the performance of the deformation joint and causes some walls to crack.

1.4.2 The sealing material embedded in the deformation joint has poor water tightness, and the cover plate is improperly constructed, which can not meet the normal work of the deformation joint, resulting in the cover plate being pulled open and leaking.

1.5 window and its hole leakage.

1.5. 1 The sash material has a thin thickness and a small cross section. In manufacturing, the connection structure is not tight and firm, which leads to the defects of poor plane stiffness, large deformation, serious deterioration of sealing performance and cracks caused by shaking when opening.

1.5.2 The width and height of the notches of the window frame and sash are not matched, the overlapping gap between the middle seam and the tongue-and-groove is not vertical, and the rubber strip, wool top and silicone strip are broken, dislocated, missing corners and not in place, resulting in poor "three properties" indicators of doors and windows. At the same time, the limiting device at the top of the window sash leaks or is set irregularly, which leads to derailment and ship jumping when the window sash is opened or in heavy wind and rain.

1.5.3 The side frame is not tightly engaged with the glide slope, and there is a gap; The window frame is not well overlapped, and the water baffle of the slideway is low. The drainage hole can drain normally when there is no wind pressure or when the wind pressure is small, but when the wind pressure is large, the accumulated water cannot be discharged or even flows backwards. There is no sealant in the gap of frame material flat-fell seam, which causes water seepage at flat-fell seam; The rubber sealing strip or water blocking brush strip for installing glass is not in place or falls off.

1.5.4 The performance of building door and window materials is quite different from that of wall materials; The sealing groove is not set as required or the notch is too shallow; The sealant is not tightly blocked, the dust on the surface of the notch is not cleaned before gluing, the sealing material does not meet the requirements, and the temperature change causes gaps between the interfaces, resulting in leakage.

1.6 temperature cracks and uneven settlement cause wall cracks and leakage.

1.6. 1 uneven settlement or stress changes occur in the frame and frame-shear structure, and horizontal or 45 cracks occur in the yin-yang angle of the infilled wall, the openings of doors and windows, the wall under the window and some weak parts, resulting in leakage.

1.6.2 the masonry speed of the infilled wall of the frame structure is too fast, and the mortar joint of the wall begins to fill the bottom joint of the beam without shrinkage or serious compaction.

At the junction of 1.6.3 column, reinforced concrete shear wall and infilled wall, due to the different expansion coefficients of concrete and brick masonry, they contract unevenly under the influence of temperature, resulting in cracking and leakage under the action of temperature stress.

Cement mortar should be used for leveling, and the smooth concrete wall should be chiseled; Before plastering, water and wet it 1 ~ 2 days, and the wetting depth is 5 mm ~10 mm. Before plastering, brush it with 802 glue slurry mixed with 10% to enhance the cohesiveness of masonry surface and external painting.

2.3.2 Using polymer cement mortar with waterproof and anti-crack function or adding a certain amount of building fiber into the mortar can effectively prevent and inhibit the formation and development of cracks caused by factors such as drying shrinkage and temperature change, and improve the anti-crack performance of plastering mortar. Plastering should be carried out in layers, the thickness of plastering at one time should not be greater than lOmm, and there should be enough interval between the two layers of plastering (when the current plastering strength reaches 1.2MPa). A layer of 200mm wide steel wire mesh should be laid at the junction of different matrix materials to prevent temperature cracks caused by inconsistent expansion and heat conduction of the two materials; When the total plastering thickness is greater than or equal to 35mm, 35×35 steel wire mesh shall be laid to prevent cracks caused by the temperature difference between inside and outside when the plastering layer is too thick.

2.3.4 When plastering the external wall to the joint, it should be plastered and leveled at the joint end, and after sizing, the ruler can be used to cut it into the joint with an iron trowel. Before plastering the lower layer, it should be fully wetted with water, then brushed with plain cement slurry mixed with 10%802 glue, and plastered after the cement slurry is sucked into the wall. The grid strip should be soaked one day in advance before use, so that it can fully absorb water and expand, which is convenient for embedding and taking out. After plastering the veneer, gently shake the frame bar in time, and then take it out in time after it shrinks slightly. Damages and hidden dangers in construction should be repaired and handled in time to ensure the neat line angle and waterproof ability. It is suggested that stainless steel or aluminum alloy be used as permanent grating, which is both beautiful and waterproof.

2.3.5 When the exterior wall decorative layer is exterior wall paint, synthetic polymer decorative materials with strong impermeability and certain elasticity should be selected to enhance the impermeability of the wall. When the exterior wall facing layer is ceramic tile, its jointing is the key link of exterior wall waterproofing. 1: 1 polymer cement mortar should be used for jointing, which can form a unique organic composite network structure, block the cracks of mortar and achieve the purpose of seepage prevention. Special valves shall be used for connection. The quality of jointing should be uniform, compacted, dense, flat and tidy, and the groove depth should be 2 ~ 3 mm ..