Sealants – A Few Important Things To Know

When it comes to purchasing construction sealants, both for commercial construction or home maintenance purposes, it is essential to keep in mind specific terms so that you can make the best judgement for yourself.

Most people who want to purchase sealants for closing off cracks around the home can make the mistake of buying a caulk instead, as it performs the similar function of a sealant.

What are the differences between caulk and a sealant?

A caulk is formulated using low to intermediate performance compounds. Being of lower quality, they usually have a limited service life.

Some of the common types of caulking materials available in the market are Acrylic Latex, Butyl, Butyl Rubber, Co-polymers, putty etc. A sealant is typically the more preferred between the two. It is put together by combining high-performance compounds that thereby contribute to its properties of less shrinkage, excellent weathering and UV resistance. Since it is put together with more expensive compounds, it also gives a better shelf life than caulks (life cycles of 10-20 years)

Why do we use joint sealants?

  • Seal penetrations or joints between construction elements
  • To stop the seeping in of water/moisture to building interior or through joints/gaps
  • By not allowing the water from seeping in, water damage and mould development are controlled
  • Prevent reinforced concrete corrosion
  • Prevent structural steel damage
  • Accommodate movement
  • Work as Part of Air Barrier System
  • Act as Part of a Vapor Retarding System
  • Acoustic Control

Now that we have an idea about what advantages joint sealants provide us let’s take a look at the terms to know when you need to evaluate the choices of sealants in front of you.

Sealant Terminology To You

ASTM C 920  is the standard specification followed across the world for elastomeric joint sealants. Put together by American Society for Testing and Materials (ASTM); it is made up of several ASTM test methods including:

  • Movement capability (ASTM C 719)
  • Sealant hardness (ASTM C 661)
  • Tack free time (ASTM C 679)
  • Adhesion in Peel  (ASTM C 794)

Movement Capability – ASTM C 719

It is a standard designed test to measure the degree of cyclic movement (extension [+] and compression [-]) that a sealant can undergo in stimulated weathering conditions. Depending on the test results, sealants get further classified into the following movement classes

  • +/-12.5% – write what class of sealants come in this range.
  • +/- 25%
  • +/- 35%
  • +/- 50%
  • +/-100/50%

Sealant Hardness – ASTM C 661

It is the standardized test to measure a sealant’s ability to resist the penetration by a Durometer probe. The rating scale for the test ranges from 0 to 100, with the lower rating meaning that the material is more softer. The less hard the sealant, the more movement it can accommodate. n

In the same fashion, the higher the number, the harder the sealant is, and the less movement it can take.

Stress Relaxation

It is the standardized test to check if the sealant can absorb extension without sustaining additional stress on the substrate’s bond line. Sealants which are can recover quickly and entirely from deformation report lesser stress relaxation numbers than those that recover slowly.

Modulus

Sealants with low modulus index indicate that they create low stress at the sealant bond line. It is usually associated with a higher movement capability.

Medium Modulus sealants are typically used for general purposes and are applicable for the majority of elastomeric sealant applications

High Modulus sealants generally are not used for moving joints. Preferably, they can be in glazing applications.

Selecting the right Sealant

How do we decide the right sealant technology ? Few factors to be considered are:

 Joint Gap in mm to be sealed
 Exposure to sunlight ( UV rays)
Joint Movement – decided how flexible sealant is required
Bonding strength required
Paintable 

Silicone Sealant Technology 

 

 Gap < 3 mm , can be exposed to Sunlight ( UV resistant), high flexibility, good bonding strength 
Typical Applications 
Window perimeter sealing 

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