How to Judge the Quality of Sealant?

There are many types of sealants:

Silicone sealant,polyurethane sealant,polysulfide sealant,acrylic sealant,ms polymer sealant,anaerobic sealant,epoxy sealant,butyl sealant,neoprene sealant,PVC sealant and asphalt sealant.

Sealant mainly look at several properties:

1. Breaking strength(tensile force/cross-section area) 

2. Bonding strength(pulling force/bonding area,except for substrate damage)

3. Elongation at break(length at breaking/original length)

4. Anti-aging ability

5. Appearance(photometric,particles,bubbles)

6. Shape preservation(no wire drawing,no sagging facade)

7. Shelf Life

8. Curing Time

What causes silicone sealant to crack after curing?

Silicone sealant cracking comes in three forms:

First, cohesion failure, manifested as cracking in the middle of the glue joint.

Second, the bonding failure is manifested as the cracking on both sides of the glue joint.

Third, the mixed damage is manifested as the simultaneous existence of cracking in the middle of the glue joint and cracking on both sides. The following are the reasons leading to the failure of sealant cohesion and bonding:

Reason analysis:

1.Sealant quality problems

Over a long period of time, with the continuous precipitation of white oil, excessive shrinkage, rigidity and loss of displacement of joint colloid can not adapt to the displacement of thermal expansion and contraction of the substrate causing cracking.

The characteristics of oxime type glue: poor resistance to joint displacement cracking.

The content of crosslinking agent in the formula is small, which is not enough to generate a perfect crosslinking network structure of the sealant reaction, and there are structural defects, which can easily lead to colloid cracking.

Sealant is not used within the validity period.

2.Application reasons

The joint design is unreasonable, the joint width is less than 6mm easily lead to cracking.

The formation of a large number of bubbles in the sizing process is easy to lead to colloidal cracking.

Oxime glue sizing is too thin and easy to crack.

Uneven sizing thickness can easily lead to cracking of colloids in thin places.

When the surface temperature of the substrate is too high or too low, the gel is easy to crack after adhesive curing.

The sealant is subject to external force during the curing process, which can easily lead to cracking of the gel after curing.

Subjected to large external force or large deformation of the substrate, such as earthquakes, typhoons, etc., colloids may crack.

When the three-sided bonding phenomenon occurs, the displacement that the sealant can withstand will be limited to within ± 15% of the original design displacement, which is easy to lead to colloidal cracking.

3.Applicability

The displacement capacity of the selected sealant can not meet the joint displacement requirements.

The modulus of the selected sealant does not meet the joint requirements.

Bonding failure.

4.Application problem

The substrate surface cleaning method is improper, the solvent used for cleaning is not suitable;

The surface cleaning of the substrate can not meet the requirements of sealant application, and the surface of the substrate is not volatile and dry when the sealant is applied;

The use of improper primer or primer has failed before use;

The substrate surface is coated with excessive primer, and the substrate surface is not volatile and dry when applying sealant;

The sealant in the interface is not sufficiently compacted during the application process;

The contact area between the sealant and the substrate is too small to ensure the adhesion of the sealant and the substrate (the interface design is unreasonable);

The sealant is affected by external influences during the curing process, such as wind load, thermal expansion and contraction of the substrate;

The ambient temperature during construction is lower than 5℃, resulting in condensation and dark dew on the surface of the substrate.

5.Applicability problem

Stone curtain wall did not do pollution test, can not determine whether the sealant will pollute the substrate;

Metal, stone curtain wall using acid glue will lead to chemical reaction with the substrate;

The bonding of glass and aluminum profiles in the glass curtain wall uses acid adhesive, and the bonding of the coated glass coating surface using acid adhesive will lead to bonding failure;

Before the start of no compatibility test, adhesion test and can not ensure the adhesion of sealant and substrate. Contact between chemically incompatible assembly accessories (e.g., seals, spacers, gaskets, fixing blocks, etc.) and the sealant will cause discolouring or loss of bonding between the sealant and the substrate.

6.Quality problems

The displacement capacity, modulus and scalability of sealant after curing can not meet the requirements of use.