With the advent of the three dog days in summer, various places have entered the barbecue mode, and the temperature and humidity have increased; and the curing of the sealant needs to rely on the moisture in the air, so the temperature and humidity changes in the environment have an impact on the construction of silicone sealants. Use will have a greater impact.
The
silicone sealant must be cured before it can perform its structural bonding or sealing function, and its curing speed is related to the ambient temperature and air humidity. component products), the deep curing speed is accelerated. The changes of the above indicators may have an adverse impact on the construction and function of the sealant, so special attention should be paid during construction in summer.
Point 1: The surface drying/pulling time is too fast, which affects the trimming and use of the sealant
When the temperature and humidity of one-component or two-component products increase, the surface dry time (one-component) and the breaking time (two-component) will be shortened accordingly. Therefore, during construction in summer, for single-component sealants, a simple test should be carried out on the surface drying time before use to understand the surface drying time of the product in the use environment, so as to guide the trimming and gluing work during actual construction.
Point 2: Foaming after construction
After construction, there are bulges of different sizes on the glue joints, and after cutting, the interior is hollow. Foaming of the sealant will lead to a decrease in adhesion and poor sealing effect.
The methanol contained in the alcohol-based adhesive will release gas during the curing process (methanol begins to volatilize at around 50°C), especially when it encounters direct sunlight and high temperature. Concrete and various metal window frames are difficult to breathe. In addition, the temperature and humidity are higher in summer, and the curing will be faster. The gas released by the glue can only run out of the uncured glue layer, and the cured glue strip is on the surface. Bubbles of different sizes will appear. In the high temperature season, if you choose alcohol-based adhesive construction, you should try to avoid using it in direct sunlight, or take appropriate shading measures.
In addition, in summer, thunderstorms are frequent, and the substrate and glue joints are affected by moisture after raining. If the glue application is carried out before they are completely dried, the moisture in the glue seams and the base material can not be released into the air in time after being dissipated. Bubbling phenomenon. In this case, it is necessary to wait until the substrate or glued joint is completely dry before applying the glue.
Point 3: Drumming after construction
What is sealant "bulging"?
The curing process of one-component building silicone weather-resistant sealant depends on the reaction with moisture in the air to cure. The temperature and humidity of the environment have a certain influence on its curing speed. Generally speaking, the higher the temperature, the faster the curing. The higher the humidity, the faster the cure. The recommended construction conditions are the ambient temperature within the range of 4-40°C and the relative humidity greater than 50%RH. When the sealant cure is slow, it will take longer for the surface of the sealant to cure to a sufficient depth.
During construction in summer, the temperature can generally meet the requirements, but when the relative humidity of the environment is low (below 50% RH), the curing speed of the sealant becomes slower, and the time required for the surface of the sealant to cure to a sufficient depth will be longer. .
When the surface of the sealant has not been cured to a sufficient depth, if the width of the glue seam varies greatly (this is usually caused by the thermal expansion and contraction of the panel), the surface of the glue seam will be affected and unevenness will appear. Sometimes it is a bulge in the middle of the entire glue seam, sometimes it is a continuous bulge, and sometimes it is a distorted deformation. After the final curing of these glue seams with uneven surfaces, the interior is solid, not hollow (the hollow is called "bulge"). Bubble"), collectively referred to as "drumming".
How did "Drumming" happen?
The root cause of the "bulging" phenomenon is that the glue undergoes large displacement and deformation during the curing process, which is the result of the combined effect of the sealant curing speed, glue joint size, panel material and size, construction environment, construction quality and other factors. If the seam "bulging" phenomenon, it is necessary to eliminate the above-mentioned unfavorable factors causing "bulging".
Although the bulging phenomenon will not affect the performance of the weather-resistant sealant, it will affect the aesthetics of the curtain wall. Therefore, during construction, the bulging phenomenon after the construction of the one-component weather-resistant sealant can be improved by changing the construction time of the sealant, selecting a product with a faster deep curing speed, or taking appropriate shading measures, such as in the building in the morning. Glue is injected on the west or north side of the building, and glue is injected on the east or south side of the building in the afternoon, and ketoxime-type products are used instead of alcohol-type products.
How to avoid "drumming"?
For a certain project, it is generally difficult to control the ambient temperature and humidity, and the material and size of the panel and the design of the glue seam have also been determined. Control the temperature difference.
A. Displacement capacity of sealant:
For a specific curtain wall project, since the plate size, the linear expansion coefficient of the panel material, and the annual temperature change of the curtain wall are all fixed values, the minimum displacement capacity required by the sealant can be calculated according to the set width of the glue joint. When it is narrower, it is necessary to choose a sealant with higher displacement capacity to meet the requirements of joint deformation.
Building joint sealants can be divided into 7.5 grades, 12.5 grades, 20 grades, 25 grades, 35 grades, 50 grades, and 100/50 grades according to the displacement capacity. The higher the level, the better the elasticity of the sealant, and the stronger its ability to withstand joint displacement deformation.
B. Sealant curing speed:
Recommendation: Use a sealant with a relatively fast curing speed. At present, most of the sealants used in domestic construction joints are neutral silicone adhesives, which can be divided into deoxime type and dealcohol type according to the curing type. The curing speed of deoxime-type silicone adhesive is faster than that of dealcoholized silicone adhesive.
In the construction environment with low temperature (4~10 ℃), large temperature difference (≥15 ℃) and low relative humidity (<50%), the selection of deoxime silicone adhesive can solve most of the "drumming" problems . The faster the curing speed, the stronger the ability of the sealant to withstand joint deformation during curing, the slow curing speed of the sealant, and the large displacement deformation of the joint, which is prone to "bulging" of the glue seam.
C, environmental temperature and humidity effects:
The curing of one-component building silicone weather-resistant sealant can only be cured by reacting with moisture in the air, so the temperature and humidity of the environment have a certain influence on its curing speed. Generally speaking, the higher the temperature and humidity, the faster the reaction curing speed.
When the temperature and humidity are low, the curing reaction speed is slow, and the phenomenon of "bulging" of the glue joint is prone to occur. The best recommended construction conditions are: the ambient temperature is 15 ℃-40 ℃, the relative humidity is > 50%RH, in rainy weather conditions Construction glue is not recommended.
D. Construction time selection:
What should I do if the relative deformation of the glue seam (absolute deformation / glue seam width) is too large due to low humidity or temperature difference, glue seam size, etc., no matter what kind of sealant is used?
1) Hurry up for construction on cloudy days, because the temperature difference between day and night on cloudy days is small, the deformation of the glue joints is small, and the bulging phenomenon is not easy to occur.
2) Take appropriate shading measures, such as shielding the scaffolding with dust-proof nets, so that the panels are not directly exposed to sunlight, reduce the temperature of the panels, and reduce the deformation of joints caused by temperature differences.
3) Choose the right time to apply glue.
Appropriate construction time for building facades in different directions
The east façade should be constructed when the sunlight shifts to the south, such as after 12 noon;
The south façade should be constructed when the sunlight shifts to the west, such as after 15:30 in the afternoon;
The west facade should be constructed when the sun is about to go down, such as after 16:30 in the afternoon;
The north façade is generally not exposed to sunlight, the probability of bulging is very small, and the construction time is not limited.
E. Other measures:
1) Glue the glue seam twice. That is, make a concave glue seam first, wait for it to cure for 2~3 days, and after it has elasticity, apply a layer of sealant on its surface.
2) Using open-cell backing material to accelerate the curing speed.
Point 4: Storage
1. In the high temperature in summer, please keep the indoor temperature of the warehouse not higher than 35 ℃ and avoid direct sunlight;
2. During the rainy season, pay attention to moisture protection and keep the warehouse in good ventilation. Place a moisture-proof board on the ground or use other auxiliary tools to lift the glue pile to keep the air at the bottom of the glue pile smooth and avoid the moisture on the ground affecting the quality of the glue;
3. Store in dry and vacuum sealed to isolate air and water. If the half pipe is not used up, just leave it as it is. The nozzle part will harden and seal by itself. The one that hardens the nozzle when it is used next time You can continue to use it by picking out or extruding the small dots.
