10 Q&A: Common problems and solutions about joint sealant application

19 / 07 / 2021

10 Q&A: Common problems and solutions about joint sealant application
During the construction process of joint sealant, you might encounter different problems, such as the joint sealant turn yellow, crack, bubbles sagging and oil permeation, etc., we have listed some common problems after applying sealant in this article, hope it will help.

Q1: Why do some neutral sealants not work well or even lose adhesion on aluminum-plastic panels, plastic-steel doors and windows?
A: This phenomenon usually occurs on alcohol-based neutral sealants. The compatibility of materials on aluminum-plastic panels, plastic-steel windows and doors is not good with alcohol-based silicone sealant so that influences the bonding effect.
Ketoxime neutral sealant is recommended for clients when comes to this situation, which will reduce the occurrence of it greatly. If clients choose alcohol-based neutral sealant, the surface of substrates should be wiped with acetone or xylene firstly, and sealant application should be done after the surface drying completely but within one hour. Therefore, due to the diversity of substrates, we repeatedly claim that users should do tests for compatibility between sealant and substrates according to their demands, so they could observe if it matches the requirement.
Q2: Why are there many bubbles (exterior wall) after sealant applied in the junction of concrete and metal window frame, but some not? Is it about quality problems? Why did this phenomenon not happen before
AThis phenomenon occurs on neutral sealants of many brands, it’s ensured that it’s not about quality after careful inspection and repeated tests. Because there are alcohol-based sealants and ketoxime sealants, the methanol in alcohol-based sealants will release gas(methanol starts to volatilized at 50) while curing, especially, the reaction is more intense when comes to direct sunlight and high temperature.
Otherwise, concrete and metal frame are difficult for volatilization, due to the high temperature and humidity in summer, curing will become faster, gas released from sealant will go out from the under-curing sealant layer, then there will be some bubbles of different sizes on the cured sealant. But ketoxime sealants don’t release gas while curing, so there won’t be bubbles. However, if technique and recipe can’t be mastered well, ketoxime neutral sealant will shrink and crack when comes to low temperature while curing in winter. Of course, it can be avoided if the technique and recipe are qualified. In past, silicone sealant is seldomly used in these areas by construction companies, usually, acrylic waterproof sealing materials are chosen. So, the bubbling of neutral silicone sealant is not very common. In recent years, silicone sealant has been widely used, which greatly increases project quality. However, due to not being familiar with material properties, improper selection of sealant causes it to bubble.
Here are cautions to solve these problems:
1. The best way is to do a partial test firstly to observe if it matches the usage requirements(Generally, the reaction can be seen in two or three days after sealant application).
2. Classify time and types of substrates clearly, then choose the proper neutral sealant: ketoxime sealant should be chosen in summer, and alcohol-based sealant should be chosen in winter.
3. Keep the construction surface clean and dry.
4. Avoid high temperature and direct sunlight while construction in summer, usually, it’s appropriate at dusk.
5. Similar projects could ask technical staff from the manufacturer for help.
Q3: Why neutral white sealant would turn pink? Why would some sealants turn back to white one week after curing?
A: Alcohol-based neutral sealant may occur this phenomenon, which is caused by the raw material-- Titanium Chromium Compound. Titanium Chromium Compound is red, and the white color of the sealant is adjusted by titanium pigment. But sealant is organic, and most chemical reactions are reversible, also the exist of a secondary reaction. Exactly, the temperature is the key to cause these reactions. High temperature causes a positive reaction to make color changed, but when the temperature drops and becomes stable, the reaction goes from the reversible direction, returning to its original appearance. This phenomenon should be avoided if the production technique and recipe are mastered well.
Q4: What’s the cause for neutral sealant sagging?
A: That’s because the sealant thixotropy isn’t good, the sagging is unqualified and the sealant is too thin.
Q5: What are the reasons for soft particles, hard lumps, and black spots in glass sealant?
A: The three situations may appear separately, or together. All of these are caused by mixing cured glass sealant or junk while production or sub-package. Soft particles and hard lumps may be caused by the mixture of sealant and skinning surface which has a short tack-free time, also, they may be caused by a scaping sealant in the bottom and surface of the drum while sub-package. Black spots are caused by unclean raw materials.
Q6: What’s the reason for the oil permeation of sealant?
A: Generally, sealant with oil permeation doesn’t exhibit good quality. That’s because it’s not an absolute silicone sealant, and it contains a petroleum plasticizer. The plasticizer is an oily substance with swelling, the oil will leak out if the balance between plasticizer and other substances is destroyed. In case of this situation, 100% silicone sealant with good quality is recommended.
Q7: Some glass sealants have particles with the size of the salt when applied, but some particles resolve automatically after curing, why?
A: That is the matter of the raw material formula of the selected sealant. Because some sealant contains a crosslinking agent, there will be crystallization in low temperature. Crosslinking agent condenses in sealant bottle, then there will be particles when application, but it will slowly dissolve. So, you will find particles resolve automatically after curing. But it seldomly influences the sealant quality. This situation is more affected by low temperature.
Q8: Why some glass sealants would turn yellow when reacting with sealant strips?
A: This is mainly caused by the reaction between glass sealant and PVC sealant strip.
Nowadays, to reduce cost, some businessmen would add excessive calcium carbonate to the sealant strip, calcium carbonate reacts with silicone sealant, then it will turn yellow. So, that is the sealant strip that matters.
If you choose the glass sealant with good quality, then please check the quality of the sealant strip. If glass sealant has relatively bad quality, the yellowing degree is certainly greater. If you want to avoid this problem, it’s better not to use a sealant strip, or choose a good sealant and strip.
Meanwhile, we emphasize doing a compatibility test before application on projects to observe if the glass sealant is compatible with other materials, then you can decide to use it or not.
Q9: There is a powdery substance on the surface of neutral sealant after curing, why?
A: Generally, there are several situations:
1. The selection of raw material is faulty.
2. Mixture of raw material is not homogenous.
3. It may be caused by construction conditions. If there is too much dust, it will be absorbed on the sealant surface.

Q10: What’s the reason why neutral translucent sealants turn yellow?
A: The yellowing of neutral transparent sealant is caused by the defection of sealant cement. That’s mainly caused by a crosslinking agent(curing agent) and tackifier. These two raw materials contain “Amine Group”, and “Amine Group” is very easy to cause yellowing, so some imported glass sealant may be also yellowing because of it. Otherwise, if neutral transparent sealant and acetic glass sealant are used together, it may also cause neutral sealant yellowing after curing. Also, it may be affected by the long storage time of sealants or the reaction between sealant and substrate.