Silicone Sealant Change Color? It's Not Just about Quality!

Silicone sealant has been widely used in the field of building waterproof sealing because of its excellent resistance to high and low temperature, excellent weather aging resistance and good bonding properties.

However, after the construction of a period of time, the problem of silicone sealant discoloration emerged, giving the building an abrupt "line".

There are many reasons for the partial or total discoloration of silicone sealant or glass glue, mainly in the following aspects:

1.Incompatibility of different sealant materials

Acid silicone sealant, neutral alcohol silicone sealant, neutral oxime-type sealant three can not be used together, they will affect each other and change color, acid glass glue will cause oxime-type glue yellow, neutral oxime-type and neutral alcohol type glass glue used together will also yellow.The oxime molecule released when the neutral oxime type glue is cured: -C=N-OH becomes amino after encountering acid, and amino is easily oxidized to colored substances by oxygen in the air!

2.Contact with materials such as rubber

Silicone sealant and most rubber (natural rubber, neoprene rubber, three no ethylene propylene rubber) direct contact will turn yellow, these rubber in the curtain wall and doors and Windows are widely used (rubber strips, rubber pads, etc.), this kind of discoloration is characterized by non-uniformity, and rubber directly discoloration, other parts do not discoloration.

3.The sealant was overstretched and discolored

1) Over-displacement capacity with glue, joint displacement is too large, sealant is over-stretched;

2) The local thickness of the sealant is too thin, resulting in the discoloration of the sealant concentrated in the thin part

4.Sealant is affected by environmental factors

This kind of discoloration occurs in neutral xime type sealant, the main reason for discoloration is that the air contains acidic substances, acidic substances in the air from many sources, such as curing acid silicon sealant, acrylic coatings in construction, sulfur dioxide in the atmosphere (high content in northern winter), nearby burning plastic waste, burning asphalt, etc. These acidic substances in the air can cause oxime sealant discoloration.

5.Sealant formula design defects, low quality raw materials lead to discoloration

High quality sealant features: selection of high quality raw materials, liquid content up to 40~50%, good elasticity, good aging resistance, 5~10 years of use still has good elasticity.

Characteristics of inferior sealant: high filling powder (70~80%), liquid material using recycled materials, poor elasticity, easy aging discoloration, cracking, debonding.

In addition, many manufacturers fill a large amount of white oil in the formula, and the sealant has a large shrinkage after volatilization of the white oil, which often causes discoloration and accompanied by cracks.