Case study of latex coating engineering on the outer wall

With the development of architectural coatings, the decoration of building exterior walls has been converted from solvent-based coatings to water-based coatings, water-based coatings are mainly represented by latex coatings with polymer emulsions as film products. In the past ten years, latex coatings in the Chinese market has been very good development, its manufacturers, production scale is increasing, varieties and performance is also increasing and improving. In addition to a few manufacturers of latex coating products inferior, most manufacturers latex coating production technology gradually mature, product quality is in line with or exceed GB/T9755-2001
China
. However, there are still many problems in the construction method of latex coatings in the Chinese market. Such as low quality of construction personnel, low quality of the outer wall putty, lack of field construction guidance, there is no certain construction standards and norms, resulting in the outer wall latex paint after the construction of a lot of problems, such as flowering, pan-alkali, cracking, foaming, color change, powdering, resulting in huge economic losses and case disputes. Through several typical case studies, this paper finds out the cause of the problem after the construction of the outer wall latex coating, and remedyes these engineering cases accordingly,
has achieved good results, which provides a certain reference basis for the construction of the outer wall latex coating in the future.
1 Engineering Case and Analysis
Case 1
Location and name: Dongguan Changping Town Xiangyuan Garden
Area: six six-storey buildings, a total of 14,000m2
time: June
case specifics: Case 1 used in the outer wall latex paint paint (grass green), primer and putty are produced by Guangdong Shunde Chemical Coatings Co., Ltd. After the construction of 15d, a heavy rain, large areas of the wall foaming, bubble size varies, large bubble diameter of about 5cm, small bubble about 0.5cm. After a few days, the foaming place cracks, peels, and falls off. Peeling the paint film found that the bottom putty was loose and non-strength.
cause analysis: after the opposite paint, primer, putty test, the company's paint, primer are no problem, but putty water resistance is not enough, test putty soaked in water 24h after foaming, which is the main cause of the case. Because putty water resistance is not enough, even if dry film, such as heavy rain, moisture will penetrate the bottom layer through latex coating coating film, putty water absorption expansion, become loose and non-strength, so that putty and latex paint has no binding force, resulting in paint foaming, shedding. Another reason for this case is that there are some problems in the construction. It is understood that the two putty batch scraping interval is too short, so that putty is not dried into a membrane, is sealed in the bottom layer, putty does not have the due strength, so that putty and latex paint has no binding force.
Remedy: After the weather is clear, remove the foaming paint and putty, the entire wall with 325 sandpaper polishing, choose water-resistant putty batch scraping (1 to 2) road, dry after painting.
case 2
location and name: Yunnan Kunming Material Building
area: 8 floors building, 7,000m2
time: August
, 2001 case specifics: exterior primer (transparent) and finish (tender yellow) are pure propylene latex paint, provided by a well-known foreign paint company, putty by the construction unit. Putty composition is: 60% white cement / 40% 107 glue. Two months after the completion of construction, a large area of cracking phenomenon, after sunny days, cracks are very clear, some are paint film cracking, most of the bottom putty cracking. Peel off the paint film and find that the putty is about (3 to 5) mm thick.
reason analysis: after latex paint primer and paint performance testing, the indicators are more than the national standard grade. The elastic elongation of the primer is greater than 25%, the finish is greater than 16%, and the water resistance and other properties of putty meet the requirements. The reason for this case is that putty powder is all white cement and putty batch scraped too thick caused, coupled with the construction of hot weather, high temperature, moisture volatile too fast, white cement is not well maintained, putty dry contraction, cracking, cracking large places more than latex paint elastic elongation rate, paint film pulled apart, resulting in a small number of paint film cracking and most of the bottom putty cracking.
remedy: The entire wall is polished with 325 s sandpaper, dusted off, and a high-performance outer wall putty batch is scraped twice, each thin and uniform, 4h after painting.
Case 3
Location and Name:
Area: 16 6-Storey Commercial Housing, Area 34,000m2
: July 2003
case specifics: in mid-May the project scraped bottom, bottom coating, surface coating all completed, in July, after several heavy rains, the wall a large area of color change, color from light to dark, and a shallow piece of the "flower face" phenomenon. Primers and finishes (close to lake water orchids) are provided by a local private paint factory in Chengdu, and putty is provided by the construction unit.
analysis: after the factory left a small sample laboratory analysis, primer meets the requirements, paint alkaline test (10% NaOH) 24h after color change, lower than the national standard. Several color slurry used in the coating were tested for alkaline resistance, of which the soft yellow slurry resistance was quite poor. This is the cause of large areas of color change and color from light to darkening, in which the "flower face phenomenon" may be caused by improper construction. Chengdu market external wall putty generally use white cement, talc powder and 801 glue, white cement although the hardness of putty is helpful, but the alkaline is too high, the construction side in order to catch up with the speed, putty batch scraped thick and after a few hours on the paint, did not retreat from the alkaline (according to Experience wall pH from 13 to 10, about 2 weeks) is sealed in the bottom layer, rain and water gas through the paint film penetration to putty, will be part of the alkaline into the paint film, so that the paint film resistant to poor alkaline yellow pulp color change or fade. Thus, a deep piece of shallow "flower face phenomenon", this phenomenon is common in other markets in China.
remedy: reduce the amount of white cement in putty, putty dry through with 5% to 10% of the grass acid brush (1 to 2) times, dry after painting. Choose alkaline-resistant external wall latex coating.
4
location and name: Wu hunan Yuan New Village, Anhui, commercial housing
area: 8 6 floors, 21,000m2
time: May 2004
case Specific circumstances: the project was completed in mid-May, the end of May to the beginning of June, after a light rain, most of the paint film foaming, shedding and powdering phenomenon, uneven color, shade, most of the paint film floating serious, paint film and putty loose without strength. Latex paint primer, finish (pink) by an Anhui manufacturer, putty by the construction side to provide.
: The reason for this case is two: First, the construction is in the rainy season, the relative humidity of the air is greater than 90%. Latex coating film is a process that is dried with the continuous evaporation of water and additives. With the increase of air humidity, the rate of moisture volatility in latex coatings decreases, when the water content of latex coatings and moisture content in the air maintain a balance, latex coating moisture is no longer volatile, latex coating drying is not thorough, film-forming is not good, not to achieve the due mechanical strength, paint film soft, water resistance is not enough, produce Bubbles, de-powdering and shedding, while latex coating pigments and filler density differences, due to the soft paint film so that the powder in the paint film produced a "layering" phenomenon, the density of the bottom of the sinking paint film, the density of small floating to the upper layer of the paint film, resulting in floating color and color inequality. Second, putty water resistance is not enough, tested putty is composed of a small amount of white cement, talcum powder, heavy calcium and commercially available 106 glue, putty water resistance test 30h after foaming. Because putty water resistance is not enough, putty water absorption expansion, so that putty and paint film has no binding force, resulting in paint film off.
Remedy: After the weather is clear, shovel off the peeling paint film and putty, with water-resistant putty to level, the entire wall with 325 sandpaper grinding (1 to 2) times, in relative humidity <85% of the conditions after applying two closed primers, and then paint.
case 5
location and name: Anhui Huaining Spring Park Hotel
area: 14,000m2
time: December
case specific situation: after applying latex paint 10d, paint film de-powdering, 7d after a rain, paint film large area foaming, falling off, putty also has a considerable part of the fall. After 10d, part of the paint film cracked. Latex paint primers and finishes are provided by a company in Shanghai, and putty is self-made by the builder. The ratio is: 30% white cement: 30% "double fly powder": 40% commercial 801 glue.
reason analysis: through the primer, paint performance test, quality is no problem, putty water resistance is also good. The main reason is that the construction of the outdoor temperature at that time below -5 degrees C, latex coating in such a low temperature can not be very good film, or even partially frozen milk, paint film does not have the mechanical strength it should have. Then a rain, paint film water resistance is certainly not enough; on the other hand, peel off the paint film, found putty batch scraped very thick, it is understood that putty batch scraped 6h on the paint, at such a low temperature, such a thick putty can not dry thoroughly. The above two reasons cause the paint film to foam and fall off. Paint film cracking is because the construction of latex coating in the case of undiluted, the use of roll coating, one-time roll coating is too thick, paint film dry contraction when cracking. After on-site inspection, part of the putty fell off the cement wall has grease material, in the cement wall treatment did not pay attention to.
Remedy: shovel off the putty and paint film that has fallen off, wait for the outdoor temperature is higher than 5 degrees C, wash off the wall grease with a cleanser, and then level with putty, apply two sides.
2 Exterior wall latex coating construction precautions
has been described before, in addition to a few manufacturers due to technical reasons or work-stealing material reduction caused by latex paint performance is poor, most manufacturers of external wall latex coating indicators have reached or exceeded national standards. However, the construction of outer wall latex coating has not attracted enough attention, improper construction methods, construction procedures are not standardized, the quality of construction personnel is low, the quality of external wall putty is often caused by the external wall latex paint engineering problems. To this end, this paper has done an in-depth and detailed engineering case study, put forward the external wall latex paint construction precautions for construction personnel or manufacturers for reference.
(1) paint units should choose high-quality external latex paint (primer and finish) and high-performance external wall putty;
(2) the outer wall putty selection of good water resistance, drying fast, alkaline is not high, not easy to crack, good adhesion, high hardness products. Putty batch scraping each channel to be thin and at least 4h per interval (25 degrees C, relative humidity less than 85%), such as the construction party self-matching putty, in addition to testing its water resistance, especially before painting to check whether the batch scraped putty is dry, whether the alkaline is low. Otherwise, the paint film foams, cracks, changes color, etc.
(3) should not be constructed on rainy days, foggy and windy weather. Because latex coating in these climates can not be very good film, there is no due mechanical strength, will cause de-powdering, floating color and other phenomena.
(4) to ensure that the wall is flat and solid, no loose material, grease and so on. Make sure that the putty pH of the wall and after scraping is less than 10, and the moisture content is less than 10%. (5) Do not work under conditions of less than 5 degrees C and a relative humidity size of 85%.
3 Conclusion
(1) At present, the outer wall putty on the market is generally self-matched by the construction side, they are not very clear about the properties of the material, putty properties. The common use of white cement, talc powder and low-grade 801 glue to do the outer wall putty, putty water resistance is not enough, alkaline is one of the main reasons for the project case.
(2) the low quality of construction personnel, the lack of necessary professional and technical personnel on-site guidance of construction is another cause of engineering cases.
(3) a small number of manufacturers of coatings due to technical reasons and cut materials caused by the poor quality of latex coatings on the outer wall is also one of the reasons that can not be ignored.
(4) to increase the management of the construction side, the construction personnel to carry out the necessary construction training to improve the quality of construction personnel, increase the supervision and management of manufacturers, is an effective way to reduce the case of latex coating on the outer wall.