Silicone Structural Sealant Usage Guide

1. What are the reasons for the failure of silicone sealant to bond with the substrate?

Answer: For the failure of bonding, we need to analyze from the following aspects: (1) Check whether the silicone sealant has been tested for adhesion with the substrate in advance; (2) Whether the substrate is cleaned properly; (3) Whether the curing time after gluing meets the requirements, and the curing time needs to be extended at low temperatures; (4) When primer needs to be applied on site, is the primer application appropriate? (5) Whether the gluing operation is performed under extreme conditions.

Q2. What are the solutions for the application of various plastics, such as PMMA (acrylic), PC (polycarbonate), PVC and other plastics in construction?

Answer: Since mold release agents are used in the production process of plastics, and they are easily damaged by chemical solvent swelling, the surface activity is low and it is not easy to bond. When sealant is needed, it is necessary to consider the adhesion of the sealant to the substrate and whether it will corrode the plastic. Sibao 1086 high-performance waterproof and weather-resistant sealant is a new waterproof and weather-resistant sealant for various plastic bonding applications. It can effectively solve the bonding problems of metals, glass, and various PMMA, PC, PVC and other materials.

Q3. We often encounter the problem of sealant cracking in projects. What causes it?

A. There are many reasons for sealant cracking in projects, mainly the following reasons: (1) Organic sealants such as polysulfide sealants and polyurethane sealants are not resistant to aging and cracking; (2) Inferior silicone sealants harden and crack by themselves; (3) When applying the sealant, the sealant is too thick or too thin and is prone to cracking under stress; (4) Displacement joints are also prone to cracking on three sides; (5) Improper sealant selection. According to the standard, weather-resistant sealants have multiple models such as 20, 25, 35, 50, and 100/50. However, the displacement of the actual project joint is greater than the displacement capacity of the sealant, resulting in cracking. To solve the cracking problem, we need to choose high-quality silicone weather-resistant sealants, and control the width-to-thickness ratio and the thickness of the sealant during the on-site construction process to effectively avoid the problem of sealant cracking in the project.

Q4. Irregular bubbling occurs on the surface of the weather-resistant sealant on site. What are the reasons? How to deal with it?

A: The main reasons for the bubbling problem are as follows: (1) Environmental reasons: ① When injecting glue, the joint is damp and the accessories such as the foam rod are damp, which makes it easier for bubbling to occur; ② When applying glue, the surface temperature of the substrate is too high, which will cause bubbles in the sealant; (2) Manual operation reasons: ① Discontinuity or the movement speed of the glue gun is inconsistent with the glue output speed, resulting in uneven glue application, which is easy to wrap some air and form hollow bubbles; ② Improper construction, the surface of the closed-cell foam rod is broken, and the foam rod releases gas.

Treatment method: (1) Avoid applying glue in humid, high-temperature and exposed environments; (2) Standardize the operation of glue applicators; (3) Use a suitable foam rod. It is recommended that the diameter of the foam rod is about 120% of the width of the glue seam.

Question 5. What are the reasons for irregular wrinkles and bulging on the surface of the weather-resistant glue on site? How to deal with it?

A: The bulging phenomenon mainly occurs on metal panel curtain walls, such as aluminum panel curtain walls. Due to the high thermal expansion and contraction coefficient of aluminum panels, the temperature difference between day and night is too large during the season transition period. Before the sealant is fully cured, it cannot fully adapt to the large displacement. The sealant will bulge irregularly due to the stretching and compression of the aluminum panel.

Treatment method: (1) When applying sealant to aluminum panel and aluminum-plastic panel curtain wall projects, please avoid the peak period of temperature accumulation. Construction should be carried out after 17:00 in the afternoon on the west and southeast sides. When the surface temperature of the substrate is lower than 4°C or higher than 50°C, it is not suitable for construction; (2) It is recommended to apply the sealant in two times. The thickness of the first application should be controlled at about half the depth of the gap. The second application of the sealant should be carried out the next day (the specific time depends on the degree of curing of the colloid); (3) It is recommended to choose silicone weather-resistant sealant (fast curing type) to significantly improve the bulging phenomenon.

Q6. When using single-component sealant on site, sometimes there is no time to modify it. What is the reason for the crusting?

A: The curing of single-component silicone sealant is greatly affected by the ambient temperature and humidity. At high temperatures, the surface drying speed of the sealant is accelerated. If the sealant is exposed to the air for too long after application and is not modified in time, the surface of the colloid has dried. In order to avoid not being able to modify it in time after application, a simple surface drying time test is conducted in the construction environment before construction. Modification before surface drying can avoid this phenomenon.

Q7. What is the reason for bubbles in the two-component mixture?

A When the two-component is mixed manually or by machine without vacuuming, there will definitely be bubbles in the colloid; if the air in the upper part of the barrel is not discharged after the barrel is changed when using a two-component glue machine, the air will be ejected together with the sealant during glue application, and small bubbles will also be formed in the colloid; sometimes air leakage in the glue application equipment pipeline will also introduce bubbles.

Q8. What are the requirements for the best construction environment of silicone sealant?

A The best construction environment for silicone sealant is 10-40℃ and a clean environment with a relative humidity of 40%-60%. If the surface temperature of the material is too high (above 50°C), the curing reaction speed of the silicone sealant may be too fast. The small molecules generated by the reaction will not have time to migrate out of the colloid surface and will gather inside the colloid to form bubbles, thus destroying the surface beauty of the glue joint. If the temperature is too low, the curing speed of the silicone sealant will be slower and the curing process will be significantly prolonged. During this process, the material may expand or contract due to the temperature difference, causing changes in appearance.

Question 9. Under what circumstances does the silicone sealant cure slowly?

Answer: Single-component silicone sealant cures by reacting with moisture in the air, curing from the outside to the inside. (1) It cures slowly when the ambient temperature and humidity are low; (2) Applying too thick glue may also cause the deep silicone to fail to cure. The thickness of the single-component application is not recommended to exceed 12mm; (3) In a relatively closed environment, the curing of the sealant will also be relatively slow.

Two-component silicone sealant is a colloid that cures inside and outside at the same time after the A and B components are mixed. (1) The curing speed of two-component adhesives is mainly related to temperature and mixing ratio. If the amount of component B is too small, the curing will be slow. (2) Problems with the adhesive equipment may cause an abnormal mixing ratio of components A and B. If the amount of component B is reduced, the two-component adhesive will cure slowly. (3) The construction environment temperature is too low, resulting in slow curing.