FAQ on application technology of curtain wall adhesive

2020-03-10 18:27

FAQ on application technology of curtain wall adhesive
1. Why should every project undergo a adhesion test?
Determining which solvent, which silicone, and whether to apply primer to achieve a good and consistent bonding effect is for the sake of safety.
2. The importance of material surface cleanliness?
In order to obtain good surface condition, achieve good adhesion, and meet the requirements of safety, unclean surfaces are one of the main reasons for adhesion failure.  
3. Why do we need to conduct compatibility and contamination testing before starting work?  
① Compatibility testing is mainly conducted to observe whether there is a significant reaction between silicone and gasket materials due to consideration of engineering safety and aesthetics.  
② Contamination testing is an important test method for selecting appropriate silica gel to minimize the possibility of silica gel contamination of substrates, especially stone materials.  
③ The reason for conducting these two tests is that the materials selected for each project are different.  
4. Is there an impact on the sealant due to the high acid content in the air?
It has an impact, but the acid and alkali resistance of silica gel itself is superior to most organic adhesives.  
5. We sometimes feel that the tearing force of weather resistant adhesive is not smaller than that of structural adhesive. Can we use weather resistant adhesive as structural adhesive?  
may not.  
In addition to high strength, structural adhesives must also meet a total of 4 requirements, such as large and durable adhesion, stable attenuation values, and sufficient displacement capacity.  
6. What kind of adhesion test still fails to adhere silica gel to the substrate after passing it? How to prevent it?
Due to possible differences in the substrate and cleaning methods used during construction and testing, it is recommended to use the same type of substrate as the sample being sent, with the same batch number as possible. At the same time, silica gel should be applied in strict accordance with the requirements in the test report and technical manual, and on-site adhesion testing should be conducted at any time.  
7. How long can the board be glued onto the wall?
First of all, we should make it clear that this is for structural adhesives, and it is the time for silica gel and substrate to achieve sufficient adhesion.  
In addition to the characteristics of silica gel itself, it is mainly related to environmental temperature, humidity, substrate type, interface investment, and whether to apply primer. After passing the glue cutting test according to the requirements of the technical manual, it can be put on the wall.
8. What is the flow phenomenon of silica gel and what details can prevent it?
Silica gel with low viscosity or consistency produces a phenomenon of colloidal sag due to gravity.

Avoidance: Reasonable interface design and seam control should be within a certain range. Generally, adhesive seams with a width of more than 25mm and upward facing seams are prone to flow. The specific situation should also depend on the characteristics of the silica gel itself.
9. How do bubbles occur in silica gel? How to prevent it? If there are bubbles, will it affect the quality?  
This situation is discussed in four aspects:
① "Air bleeding phenomenon of foam rod" or too fast glue application during construction without exhausting the gas in the glue joint. When placing a closed cell gasket, the surface is punctured by a sharp tool, causing air to remain on the surface. After gluing, pressure changes occur due to temperature changes, and the gas remaining in the gasket runs to the cured silicone surface to form bubbles. We call it "foam rod deflation". This can be confirmed by cutting the solidified silica gel along the air bubbles and finding air bubbles. The avoidance method is to take care not to break the surface when placing the backing material; When applying glue, pay attention to the uniform speed as much as possible to exhaust the gas in the joint. If conditions permit, perforated backing materials can be selected.  
② The reason is that the surface temperature of the material is too high during the gluing process. When the surface of the material is greater than 50 ℃, the by-products of silica gel - alcohols - that come into contact with the surface of the substrate will vaporize, forming many small bubbles at the interface between the material and silica gel, resulting in poor adhesion between the silica gel and the substrate. The avoidance method is not to apply glue when the surface temperature of the material is greater than 50 ℃.  
③ For dual component silica gel, if the air in the barrel is not discharged when changing the barrel, the air will blow out together with the silica gel during gluing, resulting in relatively large bubbles. The avoidance method is to open the exhaust valve after changing the barrel to exhaust as much air as possible.  
④ Heating of single component silica gel during transportation and storage can lead to premature aging of the silica gel, resulting in a large number of bubbles after solidification. The avoidance method is to follow our company's recommendations for storage of silica gel and store it at 30 ℃ or lower.  
Generally, bubble areas below 10% will not affect quality. If it exceeds 10%, you should copy the batch number and quantity and contact our agent or sales representative or technical personnel for advice.  
10. Is there a requirement for the use time of two component structural adhesives used for normal opening, and can they still be stored within the shelf life?  
It is recommended to use up the curing agent within 3-4 days after opening the seal.  
Depending on the sealing condition, if the curing agent is well sealed, it can be used within the shelf life.  
11. How can silicone not dry, work too slowly, or work too fast?  
Silica gel has its own characteristics.  
The curing rate of two component silica gel is mainly related to temperature and mixing ratio. When the temperature increases, the curing speed increases; Increasing the proportion of curing agent will accelerate the curing speed.  
12. Can I apply glue on rainy days? Can I apply glue if the surface of the substrate is wet?  
Wet surfaces caused by rain can affect the establishment of consistent and good adhesion. Moisture on rainy days does not affect adhesion.  
Dampness does not necessarily lead to adhesion failure, but it can prevent silica gel from performing optimally or lead to potential adhesion failure. Therefore, from a quality control perspective, we do not recommend this.  
13. What are the main criteria for determining the quality of glue?
Judging the quality of silica gel is a systematic project, and it is not possible to judge that one type of silica gel is superior to others just by looking at one or several indicators.  
The weather resistant adhesive should at least have good adhesion, good displacement ability, good weather resistance, and no pollution to the material.  
Structural adhesives need to have at least four conditions at the same time: high strength, strong and durable adhesion, stable attenuation values, and sufficient displacement capacity.  
14. Causes of Foaming of Silicone Weatherproof Seals During Construction
1) Air trapped during glue injection
Silicone weather resistant adhesives are generally injected at construction sites, resulting in poor operating conditions. The worker stands on the tripod and injects glue. The uniformity of the glue injection is not easy to grasp, and air is easily trapped in the glue seam. After the glue is applied, the surface of the glue seam is scraped and polished. The cushion rod inside the glue seam is generally closed hole polyethylene foam rod. The air wrapped in the glue seam is not easy to overflow. After the air for glue seam trimming is compressed, it will produce outward uplift tension. The weather resistant glue seam is generally wide and thin. The weather resistant glue with the ability to lift the arch and move high is low in hardness. The glue is very soft before curing. The uplift tension of compressed air will slowly support the glue seam to bubble. This phenomenon is more likely to occur in the application of weather resistant adhesives that can lift the arch+- 25% or more of the joint displacement capacity. On the contrary, some weather resistant adhesives with low allowable displacement have higher hardness and are thicker before curing. The tension of the compressed air wrapped in the glue seam is not easy to support the glue and foam. Therefore, the more weather resistant adhesive that can provide high displacement capability, the more attention should be paid to the uniformity of the glue injection. Generally, the vertical glue joint can be injected with glue from the bottom up to overcome some blistering phenomena. What is more important is the proficiency and sense of responsibility of the work operator.
2) Wet interface during glue injection
When working outdoors, we often encounter rain, especially in summer in the south. It rains almost every day. If the interface is wet after rain, glue will be injected directly. When the sun shines on the bonding substrate and glue joints, the temperature inside the interface will rise, and the moisture inside the glue joints will evaporate, which will blister the uncured and soft glue joints. Sometimes the polyethylene foam cushion rod is wet, which will also cause the glue joints to blister. Therefore, during construction, it is not allowed to blindly seek progress. Wait until the interface is dry before injecting glue, which can avoid the above situation.
3) Foam rod deflation
Generally, the cushion rod inside the glue seam is closed cell high foaming polyethylene foam rod. Due to improper extrusion during rotation, the internal air bag breaks and air is released. When the glue is just injected, there will be bubbles or bulges. The first solution to this problem is to cut the foam rod and cut it to the inside. The other is to adopt perforated foam rod or polyethylene foam rod with foam to overcome the above situation. On the other hand, there are many alcohol types of weather proofing adhesive, and alcohol type weather proofing adhesive will release ethanol when curing, and ethanol will react with some foam rods, such as foaming when silicone weather proofing adhesive is used in a construction site. If you switch to another oxime type weather resistant glue injection from the company, there will be no bubbles. In this case, the problem was solved by changing the foam rod or rubber.
4) Exposure to the sun when the adhesive is not cured
Silicone adhesive cannot be exposed to the sun before it is cured, especially when exposed to the sun just after the adhesive is injected, which can cause honeycomb bubbles inside the adhesive seam, causing the external bulge of the oxime seam. This situation is more obvious when using alcohol based silicone adhesive. This situation is difficult to overcome during construction in hot summer. When using glue injection, avoiding exposure to the sun can overcome some blistering phenomena. The specific method is to inject glue on the west or north side of the building in the morning, and inject glue on the east or south side of the building in the afternoon. After glue injection, after a period of curing, the surface layer of the glue has crusted, and when it is exposed to the sun again, it has a certain resistance, which can overcome some blistering phenomena.
5) The surface temperature of the substrate is too high
When silicone adhesive is cured, the temperature of the material to be bonded cannot exceed 50 ° C, a conclusion that has been recognized by most silicone adhesive manufacturers. When the surface temperature of the substrate exceeds 50 ° C, injecting adhesive can cause blistering of the adhesive seam, which can be encountered during weather resistant caulking of metal panel curtain walls. In hot summer, when the metal plate is exposed to the sun, especially the surface temperature of the aluminum plate will reach 80 ° C, at this time, the glue injection is very easy to cause blistering of the glue seam. Therefore, glue should be injected in the second half of the afternoon or on cloudy days to improve the above situation.  
6) Large temperature difference between day and night, large thermal expansion and contraction of the interface
This situation is more likely to occur when injecting glue into aluminum panel curtain walls. Aluminum is a material with a large coefficient of linear expansion. In spring or autumn in northern China, the temperature is relatively high during the day and night, and when the sun directly shines on the aluminum plate at noon, the surface temperature of the aluminum plate can be as high as 60 ° C to 70 ° C, and the temperature drops to about 10 ° C at night. Large aluminum plates also have more thermal expansion and contraction, resulting in greater joint displacement. After the weather resistant adhesive is caulked, the actual displacement of the interface is borne by the adhesive joint. During the curing process, excessive Repeated stretching and displacement can cause blistering in the adhesive seam, so avoid direct sunlight at noon during glue injection to improve some of the above blistering phenomena.  
7) The climate in the northern region is dry
Silicone sealant needs to be polymerized to form an elastic sealing material with the aid of moisture in the air. The amount of humidity in the air is closely related to the curing rate. The climate in northern China in spring is very dry, and the curing time of silicone sealant is very long after injection. The silicone sealant before curing is extremely susceptible to the impact of the external environment, providing opportunities for various foaming phenomena.  
15. What is the cycle required for product testing, and the size of the materials used?  
Compatibility/adhesion test: 28 days. Aluminum profile: 30mm wide, 150mm long, 4 pieces. Glass or other decorative plates: 150mm × 75mm, 2 pieces. Accessories such as double-sided adhesive tape and foam rod: 600mm, 1 piece. Contamination test: 55 days. Contamination test, 25 × twenty-five × 75mm 24 pieces.  
Recommendations: 1. Separate adhesive and compatibility tests to reduce the number of days of adhesive testing; Reduce the number of days for pollution testing; Reduce the number of test pieces for contamination testing.   
Contamination test for 35 days, base material size of 25mm * 57 mm, compatibility test for 22 days, backing material length of more than 200 mm, adhesion test for 14 days, glass base material size of 300 mm * 300 mm, aluminum material length of more than 200 mm
16. Causes of rainwater leakage in buildings caused by sealant
1) Improper construction, including missing silicone, jerry-building, or construction not in accordance with the drawings, and sealant not filling the interface, can lead to waterproofing failures that are more lethal.  
2) When external forces, gaps, and water factors coexist, water leakage will inevitably occur. Missing silicone, or cutting corners or not complying with the drawings can lead to poor sealing, leading to water leakage. At the same time, it should be noted that the sealant should fill the entire interface and be in full contact with the substrate, which can ensure good adhesion between the sealant and the substrate, and is also a prerequisite for the durability of the sealant.  
3) If the displacement capacity of silica gel fails to reach the interface displacement, it will inevitably lead to poor weather resistance, insufficient anti-aging capacity and other consequences. However, the displacement capacity of the sealant after aging will be significantly reduced, and the reason why the displacement of the plate cannot be met is that the sealant with low displacement capacity is used, or even the fake sealant.  
4) Due to the fact that three-sided bonding can limit the displacement capacity of the sealant, if necessary, an anti-sticking tape can be used to avoid three-sided bonding. Due to different forces acting on the joints at the junction, the amount of displacement is large. Attention should be paid to reserving expansion joints during design to allow the sealant to bear excessive displacement, and direct collision between the window frame and the wall should be avoided.
18. Structural assembly failure caused by sealant?  
1) The common cause of structural assembly failure is adhesion failure, which is also the most common reason. Adhesion failure indicates that the structural adhesive does not play any role and also means assembly failure.  
2) A large amount of foreign matter adheres to the surface of untreated materials, which, if not effectively cleaned, can affect the establishment of adhesion. However, there are certain differences between the types of adhesion and cleaning solvents. Cleaning the substrate with different cleaning solvents can significantly differ in adhesion strength, so the solvent should also be selected through adhesion testing.  
3) Interface design is also important in structural assembly. In addition to meeting the requirements for the width and depth of structural adhesive, the characteristics of easy construction and sealant curing are often ignored. This is the reason for most structural assembly failures. Improper design not only makes it inconvenient to apply silicone, but also makes it difficult to fill the interface, and it is not convenient to clean it. Therefore, the adhesion of silicone adhesive is not guaranteed. If a separate interface design is adopted, Place the double-sided adhesive strip with spacing action close to the four sides of the glass, and the weather resistant adhesive of the structural adhesive will be separated, so that its construction and curing do not affect each other.