Sealants are great at preventing the penetration of noise, dust, air and gas and are usually used to fill in small openings. Typically, sealants are used for concrete and drywall, but are just as effective with other materials such as uPVC.

Fundamentally, no single silicone type should be used for everything. The problem is, their descriptions are all very similar and give little away. So which one is best for the job you need doing? Read on to find out.

The most common failures in joints occur when:

  • The wrong sealant has been used for the job
  • During the manufacturing stage, the joint width/depth has been made too big or small.
  • The double glazing window joint seals have excessive movement
  • A sealant of poor quality has been used.

If you are planning to seal in a crack anywhere, ensure you consider all of the above. Before carrying out the job, make sure all the protective tape is removed, the surfaces are clean and that there is no residue. Foam packer rod should be used if the joints are wider than normal.

In the double glazing industry there are two common silicone types:

  • Neutral cure /Acetoxy cure
  • Modulus ? High/low

Modulus explained:

The modulus sealants are split into two sections ? high and low. A low modulus will stretch comfortably when put under a small force, providing elasticity and better movement. On the other hand, a high modulus sealant is very rigid.

If you?re trying to decide which modulus if right for you, take the desired movement into account. In the double glazing industry it is accepted that linear expansion and contraction of joints and plastics is high.

So, a low modulus would suit this task, as it provides the movement needed. There are sealants that can accommodate up to 50% of the normal joint width.

Cure explained

The two forms of cure available are acetoxy and neutral, but again their names give little away.

Essentially, the difference is how well that adapt to the material the sealant is used on.

  • As they cure, acetoxy sealants release acetic acid. This smells similar to vinegar
  • Whereas neutral sealants release alcohol as they cure. They have virtually no smell.

Acetoxy cure

Acetoxy cure is the sealant most widely used as it is quick to harden and the more rigid of the two. However, it is said to have poor adhesion qualities and doesn?t ?stick? well to, glass, aluminium and polycarbonate.

Another downside is that acetoxy cure attacks and degrades polycarbonate. This is because of the chemical released.

Neutral cure

This type of sealant is the polar opposite of acetoxy and sticks well to many materials. It makes neutral cure great for aluminium and uPVC double glazing, as well as glass, stone and polycarbonate.

Acetoxy takes around 30 minutes to skin over, leavening a shinier finish. Depending on the temperature, thickness and humidity conditions, it can take one to five days to fully cure.

Neutral sealant is more expensive than acetoxy.

So which sealant should I buy?

Low modulus neutral cure silicone seems to be the most adaptable on the market. Its flexibility gives it great movement and has excellent adhesion with most materials.

This makes it the best silicone out there for windows, whether it be used for uPVC, wooden double glazing or aluminium double glazing.

For the job, the worst sealant has to be the high modulus acetic cure. Short term it may do the business, but it won?t take long to become ?unstuck?.

Unfortunately, just to put the spanner in the works, there is a low modulus acetoxy cure, so be sure not to buy the wrong type.

Tip: Make sure to check the movement capabilities when comparing sealants and prices. It should be marked as a %. Be aware that cheaper silicone sealants are bulked up by other materials, such as chalk power, making it an inferior product.

Bulked up sealants have a higher shrinkage rate and can be prone to discolouration and poor adhesion.

Not every tube will have the movement capability displayed, but you can always seek out the manufacturer?s data sheet.

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