During the application of construction joint sealant, the deformation and protrusion on the surface of the joint may be "bulging" or "blistering" on the same day or within a few days of application. Although their appearance is similar, they are essentially different. The root causes and corresponding solutions of the two phenomena are also different.
"Bubbling" or "bubbling"?
? drum up phenomenon
When the curing speed of sealant is slow, it may appear that the surface has cured and the interior has not fully cured. At this time, if the width of the glue joint changes greatly, the surface of the glue joint will be affected and uneven phenomenon will appear, sometimes the whole glue joint will be raised in the middle, sometimes the continuous bulge, sometimes the distorted deformation, collectively referred to as "bulge".
"Bubbling" phenomenon
The sealant is wrapped with gas and forms a cavity on its surface or inside, which is collectively referred to as "foaming".
? comparison between "bubbling" and "bubbling"
project
Contrast
"Drum up"
Bubbling
Intrinsic performance
Protuberant colloid is solid
The protuberant colloid is hollow
Formation mechanism
Joint displacement changes greatly
Gas in glue
Harm
Affect the appearance, but not the sealing and mechanical properties
Affect the appearance, sealing and mechanical properties
An analysis of the causes of "bubbling" and "bubbling"
? cause analysis and solution of "bulge"
The "bulge" of construction joint sealant is caused by the deformation of joint displacement. In this way, the ability of the sealant to bear the deformation of the joint during curing and the change of the joint size caused by the thermal displacement become the main influencing factor of the sealant "bulge".
1. Ability to withstand joint deformation during sealant curing
The faster the curing speed is, the stronger the ability of the sealant to bear the joint deformation during the curing period is;
The curing speed of sealant is mainly determined by the formulation characteristics of sealant itself. According to the type of sealant and the activity of catalytic system, the sealant with relatively fast curing speed can be roughly judged and selected.
Solution: choose high quality silicone sealant
Fengjing 888 advanced weather resistant adhesive, selected ketoxime type formula system, the deep curing speed of the product is fast after sizing, the impact of the external environment is the smallest, which can reduce the bulging phenomenon in the sizing process; the product has been tested in practice, and has been widely used in many excellent projects at home and abroad.
Curing speed is not only related to the formulation of sealant itself, but also affected by environmental factors.
At present, single component, room temperature moisture curing system sealant is widely used in construction joints, and the ambient temperature and humidity have certain influence on its curing speed. Generally speaking, the higher the temperature and humidity is, the faster the curing reaction speed will be; when the temperature and humidity are low, the slower the curing reaction speed will be, and the phenomenon of "bulge" will easily occur.
2. Change of joint size caused by thermal displacement
After the gluing operation, although the surface of the colloid is solidified, but the deep layer is not fully solidified. When the joint material is cold drawn and hot pressed, the inside of the colloid is squeezed and stretched, which directly affects the appearance of the colloid. When the gel is completely cured, the problem of "bulging" of sealant can be seen by naked eyes.
Solution: try to avoid high temperature or low temperature construction. You can choose to apply glue on the facade avoiding direct sunlight or in cloudy weather to ensure that the ambient temperature and humidity are relatively constant.
3, foam rod mismatch
When the foam bar is filled in the glue seam before sizing, if the foam rod is selected, when the gel is not solidified, the movement of the foam stick will cause the sealant to drum up.
In addition, if the size of the foam rod does not match the size of the interface, the foam rod will be stretched too tightly during the liner and then immediately sprout. The rebound of the foam rod will also cause the sealant to drum.
Solution: choose the foam rod with a size equal to 120% of the seam width. The length of the foam rod should be consistent with the length of the joint and should not be exposed too long.
? cause analysis and solution of "bubbling"
Building joint sealant "foaming" is often caused by the gas wrapped in the adhesive. The gas sources are roughly divided into three categories: the gas produced by the curing of sealant itself, the gas released by the base material filler, and the moisture produced by the construction environment.
1. The sealant itself solidifies to produce gas
During the curing process of silicone sealant, gas will be released, especially in high temperature. If the substrate in contact (such as concrete, metal window frame and glass) is difficult to breathe, when the temperature is too high, the gas released rapidly during curing can only run out from the incompletely cured rubber layer, and bubbles of different sizes will appear on the cured rubber strip.
Solution: users should avoid construction under high temperature as much as possible, and avoid the influence of direct sunlight and other heat sources when bonding the hard to ventilate base materials such as concrete, metal window frame and glass.
2. Gas released from base material and filler
Due to the difference in the formulation of cement or concrete, some chemical additives in its composition may react with sealant, resulting in bubbles.
Solution: it is recommended to carry out small area gluing test and peel adhesion test before use, and use large area after confirming good adhesion and no bad phenomenon.
In addition, when using sealant for building joints, foaming agents and foam rods are often used for filling. During or after sizing operation, part of gas will be released from the filler itself or the gas in the closed space will be extruded by the thermal expansion of the filler, resulting in "foaming" of the colloid.
Solution: before the work, we should confirm that the foam is completely solidified in the adhesive seams, the foaming agent, the foam rod and the sealant should be kept relatively smooth, so as to avoid excessive extrusion in the adhesive work. Avoid construction under the environment with large temperature difference change in a short time.
3. Water vapor generated in humid construction environment
If the glue joint is wet before the gluing operation, the moisture is easy to be heated and vaporized after the gluing to cause "foaming" of the sealant.
Solution: make sure that the glue joint and the base material filler are dry before the gluing operation, and avoid the construction in rainy days.
The problems of "bubbling" and "bubbling" appear in the field application of construction joint sealant, which are closely related to product quality, field construction environment, technology and other factors. Especially in the construction period of seasonal alternation, the construction shall be carried out according to the standard construction process of sealant to avoid "bubbling" and "bubbling".
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