Structural Adhesives, Silicone and Joint Sealants - What is the difference?

Structural Adhesives, Silicone and Joint SealantsGone are the days when you wanted to join materials and the first thought was to bolt, rivet, or weld. Today there is a wide range of industrial adhesives and sealants for numerous joining applications that offer a strong, secure solution that is in many instances can be better than traditional fasteners. In this blog we will investigate adhesives, joint sealants, and silicones. So, what are the differences between these products? An adhesive is a high strength product for the purpose of joining of two materials. Whilst a sealant is a low strength product that is perfect for filling and sealing gaps between different materials. This is the basic breakdown; however, you will find there are numerous adhesives that work well as a joint sealant and vice versa. Silicone can be engineered to be both an adhesive and a sealant. Silicone is the the go-to caulking product with numerous trades in the construction and building industry. Understanding your application and the results you are seeking is the most important consideration is selecting the right product.

What are the key advantages of adhesives, and joint sealant?

Adhesives and joint sealants offer numerous advantages over other types of fasteners including.

  • Invisible fastening solution for a clean smooth finish compared to traditional fasteners.
  • Provides uniform distribution of weight over a larger surface making for a better bond.
  • Spreads and absorbs stress better than a single point metal fastener.
  • Facilitates and compensates thermal movement between different material types.
  • Time & cost effective; better productivity compared to the use of metal fasteners.
  • Excellent seal against most elements including moisture, salts, UV light and so much more.  

What are the main types of adhesives?

There are numerous types of industrial adhesives and we will review the different chemical composition with the aim of providing an overview with examples of MS Polymer, Polyurethane, Epoxy, Polyamide, and Acrylic etc.

MS Polymer.

This is the latest generation high performing environmentally friendly adhesives originally from Japan. They are a hybrid between silicone and polyurethane, with all the advantages of each product and none of their disadvantages. An easy-to-use all-rounder that requires little surface preparation. Examples of this product include Bond Flex, Bond Flex Plus, Bostik’s Xtreme, Soudal’s T-Rex and numerous other products.  Medium price range.


Polyurethane is another strong flexible adhesive, they bond well to a wide range of material including plastic, metal, and timbers, making them very popular in both the construction and industrial sectors. Examples of this product include Bostik’s Matrix FC, Sika 252, and many other great products. Low price range.


Epoxy is a two-part adhesive that forms when you mix epoxy resin with a hardener. These two different substances are stored in separate containers and mixed when ready to use. Epoxies are not as flexible as MS polymers or polyurethanes however they have better shear strength with longer open times, allowing for the assembly of complex shapes. Epoxies adhere to a wide range of  surfaces like metals, fibreglass, timber, plastics, stone, concrete etc. Examples of an epoxy include Lord’s 310 series, Dunlop’s Builders Bond, Selleys Araldite and many more. High price range.

Dunlop Builders Bond

Dunlop Builders Bond

Selleys Araldite

Selleys Araldite


There are numerous acrylic adhesives, including MMA's, cyanoacrylate etc. Methyl methacrylate adhesives (MMA’s) are a type of acrylic that comprises resin and hardener. When cured MMA’s forms a strong bond with excellent resistance to shear, peel and impact stresses. Examples of acrylic adhesives include Crestabond M1 series, 3M Scotch-Weld, Super Glue, Loctite H8000 etc. High price range.

3M Scotch-Weld

3M Scotch-Weld

Loctite H8000

Loctite H8000


Looking for an adhesive for high temperatures? Polyimide provides excellent thermal resistance in the temperature range 240 – 500 degrees. High price range.

There are numerous other types of adhesives including, white craft glue, yellow timber glue, hot glue, spray adhesive etc.

What are the main types of joint sealant?

There are many types of sealants that are largely based on their chemistries make up, each sealant’s suitability to an application is based primarily on its performance properties. Some of the popular sealants here include, polyurethane, silicone, MS polymer, polysulfide.

MS Polymers.

These are newcomers to the sealant world and cure to be fully elastic after curing. Suitable for a wide range of materials, with little surface preparation. Examples of MS Polymer sealants include Soudal Multibond SMX50 & Bostik Xtreme Flex. Medium price range.


Polyurethane sealants are tough—even abrasion-resistant sealants and unlike silicone sealants, they can be painted. They have excellent adhesion and good movement capability however they cannot be used on glass. Examples of polyurethane sealants include Aerobolts Seal Flex, Bostiks Seal N Flex 1 and Sikaflex’s 11FC & 221. Low price range.


Butyl sealants are synthetic rubber blend materials that demonstrate a strong adhesion to a wide variety of materials including metal, glass, concrete, timber etc. Butyl forms a tough skin but remains permanently plastic underneath. Ideal for sealing joints in applications such as curtain wall joints, metal panel joints, door frames, drains, windows, or against a neoprene or EPDM surface. Known to withstand vibration and a little difficult to apply, examples of this product include Selleys Butyl Mastic or Bostik’s 5612 Mastic. Low price range.

Bostik 5612 Mastic

Bostik 5612 Mastic

Selleys Butyl Mastic

Selleys Butyl Mastic


Polysulfide sealants are water & chemical resistant but do not tolerate much movement. Most common in swimming pools and other locations where submersion must be tolerated. Polysulfide sealants often require a primer. They tend to be relatively expensive.

Other sealants include latex, acrylic & silicone which we cover below.

What is silicone?

Selecting the right silicone is not as straight forward as buying any product off the shelf. There is not a single option for everything, as there are many different types with various degrees of strength, and flexibility. Silicone is ideal for a wide range of applications, they are highly flexible with a great resistance to UV light and, extreme temperatures, however they are not paintable. Silicone comes from silica, which is a derived from sand, its predominantly used as a joint sealant, but can be engineered for structural glass applications and many other options including high temperature resistance, high movement resistance, mould & mildew resistance etc. It is an endless list, fortunately for us most silicones are sold via their application.

What is the difference between neutral and acetic cure?

This is terminology that is associated with silicones. Neutral cure means the silicone will release an alcoholic vapour as it cures. Normally these silicones will have better adhesive properties with a wider range of material and applications. A great all-rounder of a neutral cure silicone is Bostik’s Industrial Grade Silicone.  This product has superior adhesive properties, that works well with numerous materials and is Aerobolts number 1 silicone. Acetoxy silicones release an acidic vapour (smells like vinegar) as they cure. An example of this is Bostiks RTV 922, this is a high temperature industrial silicone.

What does low & high modulus mean?

Low modulus silicones have better elasticity, which means they can accommodate material movement better. An example of this would be the popular Bostik’s 5CLM. Whilst high modulus means a more rigid silicone, an example of this is Bostik V60. V60 is a superior adhesive and sealant for painted and anodised aluminum and glass.

Structural Adhesives, Silicone and Joint Sealant Summary

Today we have covered the structural adhesive, silicone, and sealant category. Hopefully, this blog has taken the mystery out of these products and removed the anxiety out of selecting the right product for your application.  Here at Aerobolt we have a comprehensive range of structural adhesives, silicones and joint sealant that can assist in your application, in fact Aerobolt has a range of high-quality products that perform well in almost any application. Simply call us on 02 9755 3747 or contact us for all your sealant requirements.

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