Glass bonding adhesive; Choosing the best glue to bond glass - Forgeway Ltd

When bonding glass, you will come across several different adhesive options. For years, polyurethane adhesives have been the go-to option. But they aren’t the only adhesive you can use to bond glass.

Here at Forgeway, we manufacture and supply a range of different adhesives and sealants. We know that bonding glass requires a specialist adhesive. You could be looking for a suitable alternative to polyurethanes or you could be looking for a glass bonding adhesive for the first time. Either way, we’ve got you covered.

This article will discuss what makes glass bonding difficult, what you need from a glass bonding adhesive, and what we would recommend as the best glass bonding adhesive.

Is it difficult to bond glass?

Yes, bonding glass is difficult. Glass is heavy and rigid, which means you can’t just use any adhesive.

On top of that, the adhesive is usually the only form of fastening used when joining glass. Mechanical fasteners are rarely used because they put stress on the glass and will require you to pre-drill holes. 

The other thing to remember is the threat the glass could pose if it were to come loose. Several countries have even gone so far as to introduce national standards to try and reduce this threat. 

The US, for instance, has introduced FMVSS212 which is specifically for windows in vehicles (cars, trucks, buses etc).

Germany has the DIN 6701 standard which is for all bonded joints in the rail industry but has also introduced DIN 2304 more recently which is for other sectors where there are bonded joints (construction, automotive etc).

The DIN standards state that glass bonding would typically qualify as high risk or sometimes very high risk. This means that you have to take extreme care when choosing the correct adhesive for bonding glass to ensure it meets these standards (depending on your national regulations of course). 

All these factors contribute to making glass bonding so challenging.

Where would you need to bond glass?

Some typical examples of bonding glass are:

• Windows and windscreens in vehicles, boats, aeroplanes, and trains.
• Bonding windows in construction
  
  

This article will be using the first example for demonstration purposes. All the different sectors face different challenges, and the adhesive you choose will have to be able to withstand those challenges.

For example, adhesives for bonding boat windows will have to withstand significant exposure to salt and UV. Whatever you are bonding, you will need to consider what other characteristics you need from your adhesive before deciding on the best option for you. 

But before that, you need to be sure that the adhesive is a suitable option for bonding glass in the first place.

What do you need from a glass bonding adhesive?

Bonding glass isn’t easy but there are a few characteristics that a glass bonding adhesive must have to be a suitable option:

• High flexibility combined with high strength: People often overlook flexibility as an important characteristic of an adhesive. When it comes to bonding glass, flexibility is essential. Nonetheless, you have to combine that flexibility with high strength otherwise you run the risk of the glass coming loose. A glass bonding adhesive must be flexible and strong.
• High grab with good extrudability: The adhesive must have the right balance between viscosity, grab, and extrudability. High grab means that the adhesive will help hold the glass in place while the curing process takes place. A highly viscous adhesive will provide the best grab but will be extremely difficult to work with. So the adhesive needs to be a good grab but have good extrudability too.
  
  

These characteristics above are essential in a glass bonding adhesive.

But there are a few other characteristics that are nice to have in a glass bonding adhesive:

• Long open time combined with fast cure time: Open time refers to how long you have before the adhesive forms a ‘skin’ that is unworkable. The adhesive ideally needs to have an open time of 15-20 minutes. This will allow you to allow the correct amount of adhesive and ensure the glass is properly in place before the curing process begins. After the glass is in place you need the glue to cure quickly. The fast cure is ideal because you don’t want to be waiting for ages for the glue to reach a sufficient strength to be put in use (handling strength).

• Primerless to save time: Most adhesives require extensive surface preparation to ensure the adhesive forms a strong bond to the glass. Sometimes primers are needed to paint on both the glass and the substrate it’s bonding to. A primerless adhesive also eliminates the need of removing any old adhesive, abrading, and priming the surface before bonding. 

The last two characteristics aren’t essential to a glass bonding adhesive though even though we would thoroughly recommend you choose an adhesive that meets these characteristics. 

You also need to decide what other characteristics you need from your adhesive (think UV resistance, no health risks etc).

Choosing the best glass adhesive for you

So, when it comes to making a decision, you face three potential adhesive solutions. Knowing what you need from your adhesive will help you decide which one is best for you.

Here at Forgeway, we manufacture both polyurethane and MS polymer adhesives. We know that silicones, polyurethanes, and MS polymer adhesives are all suitable options as glass bonding adhesives. 

As we mentioned already, polyurethanes are a very common choice when choosing a glass bonding adhesive. Their strength combined with their flexibility means they are a suitable option. However, they sometimes have limited flexibility, especially at high strengths.

Silicones are also an option for bonding glass. And although silicones are typically used as a sealant as they are extremely flexible. The strength is often where silicones lack. 

MS polymer adhesives are stronger than silicones and more flexible than polyurethanes. Whilst they don’t have as much strength as polyurethanes or as much flexibility as silicones, MS polymers combine the two to make the ideal glass bonding adhesive.

We would always recommend using an MS polymer adhesive for bonding glass. They are primerless, have high strength and flexibility, and have very good grab capabilities. If you are interested, check out our range of glass-bonding MS polymer adhesives.

Alternatively, if you want something that is higher strength, we would recommend you look at using a polyurethane adhesive. Silicones will provide you with more flexibility but shouldn’t be used for bonding larger and heavier glass items.

Still stuck? A member of our team can help you out if you still can’t decide which option would be best for you.