How to Prevent "Bulging" in Construction of Natural Cure Silicone Sealants?

The root cause of the "bulging" phenomenon lies in the displacement and deformation experienced by the sealant during its curing process. It results from a combination of factors, including the curing speed of the sealant, the dimensions of the joint, the material and dimensions of the panel, construction environment, and construction quality. To address the "bulging" phenomenon in joints, it's essential to eliminate the adverse factors leading to it.

While the "bulging" phenomenon doesn't affect the performance of weather-resistant sealants, it can impact the aesthetics of curtain walls. Therefore, during construction, measures can be taken to improve the occurrence of "bulging" after the application of single-component weather-resistant sealants. For instance, adjusting the construction time of sealants, opting for products with faster deep-curing rates, or implementing appropriate shading methods. For example, applying sealant on the west or north side of a building in the morning and on the east or south side in the afternoon, and selecting ketoxime-type products as a substitute for alcohol-type products.

For a specific project, it's often difficult to manually control environmental factors like temperature and humidity. Panel materials and dimensions, joint design, etc., are predetermined. Therefore, control can primarily be exercised over the type of sealant (displacement capacity and curing speed) and variations in ambient temperature.

Displacement Capacity of Natural Cure Silicone Sealant

In a specific curtain wall project, since factors such as panel size, the linear coefficient of panel material, and annual temperature variations are constants, the required minimum displacement capacity of the sealant can be calculated based on the preset joint width.  Narrow joints require silicone based caulk with higher displacement capacities to accommodate joint deformations.

Natural cure silicone sealants are categorized based on their displacement capacity, such as 7.5, 12.5, 20, 25, 35, 50, and 100/50 levels. Higher levels indicate better elasticity and stronger resistance to joint displacement deformation.

Curing Speed of Natural Cure Silicone Sealant

It's recommended to use neutral silicone adhesive with relatively faster curing speeds. Currently, most architectural joint sealants in China are neutral silicone sealants, classified into oxime-type and alcohol-type based on curing mechanisms. Oxime-type silicone sealants cure faster than alcohol-type ones.

In construction environments with lower temperatures (4-10°C), significant temperature differences (≥15°C), and lower relative humidity (<50%), using oxime-type silicone sealants can address most "bulging" issues. The faster the curing speed, the better the sealant's ability to withstand joint deformations during curing. Slow-curing sealants, combined with significant joint displacement deformations, are more likely to result in "bulging."

Effect of Ambient Temperature and Humidity on Natural Cure Silicone Sealant

The curing of single-component architectural natural cure silicone sealants relies on reacting with moisture in the air. Therefore, both temperature and humidity have an influence on curing speed. Generally, higher temperatures and humidity result in faster reaction and curing rates.

In conditions of lower temperature and humidity, the curing reaction slows down, making the "bulging" phenomenon more likely to occur. The recommended optimal construction conditions are as follows: an ambient temperature between 15°C and 40°C, and relative humidity above 50% RH. It's not advisable to apply sealants during rainy weather.

Selection of Construction Time for Natural Cure Silicone Sealant

If excessive joint deformation occurs due to factors such as low humidity, temperature differences, or joint dimensions, leading to persistent "bulging" even with various sealant choices, what can be done?

• Opt for construction on cloudy days when temperature variations between day and night are smaller, resulting in less joint deformation and less susceptibility to the "bulging" phenomenon.

• Implement appropriate shading measures, such as using dustproof nets to cover scaffolding, preventing direct exposure of panels to sunlight. This helps reduce panel temperature and diminishes joint deformations caused by temperature differences.

• Choose a suitable time for applying sealants.