Discover causes and solutions for the abnormally slow curing of two-component silicone structural adhesive in winter. Learn how low temperatures affect pot life, mixing ratios, and curing mechanisms, plus practical tips to ensure reliable bonding performance in cold conditions.
A long-term client suddenly messaged us on WhatsApp, complaining that the two-component silicone structural adhesive they were using was curing very slowly and asking if the curing speed could be adjusted. Upon receiving this message, we immediately initiated our after-sales process. Let’s see how we handled it.
First, we checked the production batch number of the goods used by the customer in the ERP system, retrieved the product testing data from the Weidu laboratory, and provided it to the customer. We also discussed the customer’s feedback with the R&D engineer. In November, Saudi Arabia is in the transition season between summer and autumn, with temperatures around 20°C and very dry air, with humidity below 20%. The R&D engineer indicated that the abnormally slow curing speed should be primarily attributed to the local seasonal change and climate change. Secondly, we considered the possibility of equipment malfunction or incorrect product usage.
Based on the product and equipment specifications, we provided the client with several areas for investigation:
① When replacing the B component container with a new one, ensure the silicone oil on the cover is evenly mixed into the black glue and thoroughly stirred.
② Semi-automatic glue applicator: 1. Clean the B component filter in the machine, as a clogged filter may cause insufficient black glue supply. 2. Remove the proportioning pump from the machine and clean the ball bearing at the directional valve port, as impurities may prevent the ball bearing from returning to its original position, resulting in insufficient black glue supply.
③ Fully automatic glue applicator: Check and clean the sealing needle valve seat (check valve) on the B component pipeline to prevent incomplete closure of the check valve due to malfunction or impurities, which could lead to insufficient black glue supply.
Meanwhile, we asked our customer to use an electronic scale to take two samples each of component A (70g) and component B (5.3g), and manually mix them. One sample was placed in a normal indoor environment (21℃, 16% humidity), while the other sample was placed in an environment with higher temperature and humidity. The curing status of both samples was observed hourly, and the surface drying and deep curing times were recorded and reported back to us. This comparative test can quickly and accurately pinpoint the cause of the slowed curing speed: is it a product quality issue, equipment malfunction, or environmental change?
Curing principle of two-component silicone sealant
After components A and B are mixed, component B first undergoes a hydrolysis reaction using the trace amounts of moisture in component A, and then initially cross-links with component A. However, to achieve deep curing, the moisture in component A alone is far from sufficient; it also needs to continuously absorb moisture from the outside air. In autumn and winter, when both temperature and humidity decrease, the surface drying and deep curing speed of the sealant will slow down. In this case, the amount of component B can be appropriately increased to accelerate the surface drying and shallow curing speed of the sealant.
To improve the deep curing speed, the ambient humidity needs to reach 75% to 85% and the ambient temperature needs to be no lower than 25°C. In this case, it is advisable to build a closed glass room, install an industrial humidifier inside, and then place the insulating glass products that need to be delivered quickly in the glass room to accelerate the curing of the sealant.
The curing speed of silicone sealant depends on ambient temperature and humidity.
The curing process of silicone sealant requires moisture from the air to penetrate the sealant and participate in the reaction. When the humidity in the construction environment is too low, the curing process will be significantly prolonged. In addition, lower ambient temperature will slow down the hydrolysis and condensation reactions, thereby prolonging the surface drying and deep curing time.
Abnormal curing speed due to construction reasons
If the curing speed of the same batch of sealant is significantly inconsistent after application, with some curing quickly and others slowly, this situation should be primarily attributed to uneven mixing of components A and B or insufficient supply of component B.
When using two-component silicone sealant after opening, component B needs to be thoroughly stirred and mixed to ensure the silicone oil is fully incorporated into the black adhesive. Incomplete mixing can result in areas with too much silicone oil and too little hardener, leading to inconsistent curing speeds or even failure to cure. Furthermore, for semi-automatic or fully automatic dispensing machines, regular inspection and cleaning of machine components are necessary. A malfunctioning or clogged check valve in the black adhesive pipeline can prevent complete closure, causing insufficient supply of component B and resulting in poor curing.
We quickly received video feedback from the customer; the comparison of the two samples clearly showed that the sample placed in a high-temperature and high-humidity environment (32℃, 55% humidity) dried faster than expected. This experimental result fully demonstrates that the curing speed of silicone sealant is highly dependent on ambient humidity and temperature. After understanding this principle, the customer improved the temperature and humidity of the application environment, and the curing speed of the sealant was greatly improved.
The customer then raised a new question: Why does silicone sealant cure much faster than silicone structural adhesive under the same conditions? We conducted comparative tests on Weidu sealant and Weidu structural adhesive, as well as sealants and structural adhesives from multiple brands on the market. The conclusion is that the sealant’s A component has a low content of 107 silicone rubber, resulting in a lower molar number of silanol units per unit volume and a lower degree of crosslinking with component B, allowing for rapid surface drying and deep curing.
Conversely, the structural adhesive’s A component has a high content of 107 silicone rubber, requiring a higher degree of crosslinking and a longer reaction time, resulting in slower surface drying and deep curing. Additionally, some brands add calcium carbonate to component B, reducing the content of crosslinking and coupling agents, thus lowering the water vapor consumption required for curing agent hydrolysis and indirectly accelerating the curing speed. However, this results in a loss of cohesive strength and adhesion to the substrate for both sealants and structural adhesives, and significantly reduces the storage reliability of component B.
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