Five standards for sealant selection and detailed analysis


1.  Quality requirements of structural adhesives

1.1 Structural adhesives have many specifications. Generally speaking, there are four essential properties: good cohesiveness, sufficient strength, appropriate displacement capacity and long-term durability. In order to satisfy the four factors, special formulation of silicone gel must be adopted.

1.2 The strength and displacement ability of structural adhesives are mutually restricted. The displacement ability decreases with the increase of strength, and vice versa. Therefore, special formulations of structural adhesives are needed to meet these two indexes.

2. Quality Requirements for Weather Resistant Adhesives

2.1 Weatherproof adhesives should also have four basic characteristics, good durability, certain modulus, appropriate displacement capacity, durability and protection of building appearance.

2.2 The importance of cohesiveness is self-evident. The non-cohesiveness of the base material is one of the reasons for building leakage. Good flexibility means lower modulus and better displacement ability.

2.3 Lower modulus surface sealant will produce less stress on the interface during tension, which is beneficial to the durability of sealant bonding. Good displacement ability means that sealant is not easy to crack because of too large displacement of sheet interface.

2.4 The service life of sealant depends on its durability. It can not be cracked by ultraviolet radiation. Moreover, improper use of sealant will affect the beauty of buildings. The pollution and hanging phenomenon caused by sealant is very obvious, and there is no aesthetic feeling.

3. Quality inspection of sealant

(1) Structural adhesives must be destroyed by cohesion.

1.1 The cut section of structural adhesive should be uniform in color, and the injection should be full and dense.

1.2 The injection width and thickness of structural adhesives shall meet the design requirements, and the width shall not be less than 7 mm and the thickness shall not be less than 6 mm.

1.3 To make a cutting surface perpendicular to the glue, two vertical cutting surfaces with a length of about 50 mm are cut along the substrate surface, and silicone structural rubber blocks are pulled by hand in the direction greater than 90 degrees to observe the damage of the stripping surface.

1.4 The quality of glue was observed and checked. The thickness and width of glue were measured with a steel ruler with a grading value of 1 mm.

(2) The quality inspection of weatherproof adhesives shall comply with the following requirements

2.1 The surface of weatherproof adhesives should be smooth without cracks, and the thickness and color of the interface should be the same.

2.2 The injection should be full, smooth, compact and seamless.

2.3 The form and width of weatherproof adhesive should meet the design requirements, and the thickness should not be less than 3.5mm.

2.4 In the inspection of weatherproof adhesives, the methods of observation and cutting should be adopted, and the width and thickness of sealants should be measured by a vernier caliper with a resolution of 0.05 mm.

4. Rainwater Leakage of Buildings Caused by Sealed Collagen

4.1 Improper construction, including leakage of silica gel, Jerry work or construction according to drawings, sealant does not fill the interface, resulting in waterproof failure, more lethal.

4.2 When external forces, crevices and water factors coexist, water leakage will inevitably occur, such as leakage of silica gel, Jerry work, material reduction or construction not in accordance with the drawings, which will result in improper sealing and water leakage. At the same time, it should be noted that the sealant should be filled with the whole interface and fully contacted with the base material, so as to ensure sealant and base material. It is also one of the preconditions for durability of sealants to produce good cohesiveness between sealants.

4.3 If the displacement capacity of silica gel does not reach the displacement of interface, it will inevitably lead to poor weatherability and insufficient anti-aging ability of sealant. The displacement capacity of sealant decreases obviously after aging, and the reason why it can not meet the displacement of plate is the use of sealant with low displacement capacity, even pseudo-sealant.

4.4 Because three-sided bonding will limit the displacement ability of sealant, anti-sticking tape can be used when necessary to avoid three-sided bonding. Joints at the junction are subject to different forces, and the displacement is very large. Attention should be paid to reserving expansion joints when designing, so that sealant can bear excessive displacement, and direct window frame and wall collision should be avoided.

5. Failure of structural assembly caused by sealing collagen

5.1 The common cause of structural assembly failure is bonding failure, which is also the most common reason. The failure of bonding indicates that structural glue can not play any role, but also means assembly failure.

5.2 There are a lot of foreign bodies on the surface of untreated materials. If it is not cleaned effectively, it will affect the establishment of cohesiveness. However, there are some differences between the types of bonding and cleaning solvents. The bonding strength of cleaning substrates with different cleaning solvents is obviously different, so the solvents should also be selected through the bonding test.

5.3 interface design is also very important in structural assembly. In addition to the width and depth of structural adhesives to meet the requirements, easy construction characteristics and sealant curing properties are often overlooked, most of the reasons for structural assembly failure are produced here, improper design not only makes silicone application inconvenient, the interface is not easy to fill, but also clean and inconvenient, so the bonding property of silicone adhesives is not. It is guaranteed that the weatherproof adhesives of structural adhesives will be separated if the separated interface design is adopted and the spaced double-sided adhesives are placed near the four sides of the glass, so that the construction and curing of structural adhesives will not affect each other.