Why does the exterior wall paint finish crack? How to avoid this pit?

Shortly after the completion of many buildings, the exterior paint finishes cracked, seriously affecting the aesthetics of the building, and the water seepage of the walls caused by cracking not only affected the function of the house, but also affected the structural safety of the building, which became a hidden danger to the quality of the project.
, then, what is the cause of the cracking of the exterior paint finish? What are the preventive responses?
The cause of cracking of the exterior wall coating finish
1, the grass-roots cracking
the base of the exterior wall coating finish is cement mortar coating layer, in the condensation process will produce dry shrinkage and temperature difference contraction, if the external wall ash construction operation is not proper, it is easy to cause empty drums, cracking. Before the construction of the coating surface do not pay attention to repair and then enter the next process, after a period of time in the sun wipers, the internal cracks will gradually develop outwards, and the paint film is very thin coating surface is difficult to offset this internal stress, it will be followed by cracking .
2, putty wall cracking
due to the use of the outer wall putty quality defects, poor crack resistance, or due to improper construction operation, putty batch scraped on the wall because of dry shrink, cracking and thus affect the coating surface.
3, coating surface cracking
Some of the paint with quality problems due to poor cracking resistance, or due to improper construction, painted on the wall soon, after the wind and sun prone to dry cracking and other quality problems.
construction precautions for cracking the coating finishes of the outer walls
. 1. The ratio of cement mortar used in the construction of the mortar surface layer of the outer wall
(1) to choose the appropriate, generally using 1:2.5 mortar is appropriate, try not to use 1:1 or 1:2 cement mortar. Cement consumption is too large, mortar shrinkage is large, easy to produce cracks.
(2) in strict accordance with the external wall ash operation procedures and process construction, before the dust must be carefully removed from the grass surface dust, dirt, oil stains and brick wall ear ash. The day before the construction must be watered through the wall, after the completion of the construction of 24h, must be watered maintenance, the number of watering times per day should be determined according to climate conditions, at least twice a day, maintenance time of not less than 7 days.
(3) If the construction in the season of sufficient sunshine, should be scientifically arranged construction time, to avoid the construction in the sun, or take effective sun protection measures to ensure that the mortar surface of the yin dry, to prevent the dust mortar layer due to the sun drying too fast caused by cracking.
(4) cement mortar ash surface layer should not be too large, make full use of the subgra seam can adjust the contraction of cement mortar. In the construction of the use of triangular or trapezoidal section of the wooden strip, cement mortar surface layer for the division, the same construction section is not allowed to appear construction seam joints, the section seam should have inlay paste seams.
construction of the outer wall putty layer
(1) the construction of the outer wall putty layer shall begin after the ash layer has reached the maintenance period.
(2) putty batch before scraping should be dust mortar layer inspection, the appearance of empty drums, cracks in the site 2 to 3d in advance to repair. Remove dust from the ash surface layer, float the sand, and keep the dust layer clean.
(3) strictly in accordance with the requirements of the construction specifications and product description construction, to ensure that putty layer and dust layer bonded firmly, not cracked. At the same time, the construction to avoid sun exposure work, to ensure that the putty layer in a dry state.
(4) putty layer after the completion of the grinding process should be timely maintenance, and at the same time wash away the powder generated by grinding, so that the wall clean, in order to enter the paint surface construction.
3. Before the construction of the coating surface
(1) paint surface, we should ensure that the putty layer is flat, solid, clean, non-smooth, powdered, peeled and other defects, such as defects should be repaired in time if found in the inspection.
(2) According to the paint finish construction specifications and paint product requirements, putty base moisture content of 8% to 10% or less before the paint surface painting construction. The drying of putty base in construction is the key to ensure that the coating surface is firmly bonded and does not crack.
Spraying outer wall latex paint
(3) coating surface layer according to different functions, the use of different materials divided into several layers of brushing, the last layer of brushing construction must ensure that the previous layer of paint film surface dry and then carried out, at room temperature each interval of 2 to 4h, the construction environment temperature should be above 5oC. Each paint film before painting to carry out a careful inspection of the upper process, confirm qualified re-construction.
(4) according to the construction process and product requirements, the grass-roots ph value is required at less than 10. Therefore, the construction must first be painted with an anti-alkali primer, its anti-mold, antibacterial, anti-acid and alkali performance is good, the putty layer penetration is strong, can fully ensure that the coating layer and putty layer bonding firmly.
(5) coating surface construction, shall not be carried out in the wind level 4 or above, or rainy days, foggy days and relative humidity of more than 85% of the environment, to prevent high winds from dust pollution paint, as well as to ensure the dry construction surface. At the same time, we should try to avoid the construction in the hot sun or hot weather.
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