The different Adhesive Testing Methods; Deciding which test method is best for you

You are reading this article because you want to ensure that the adhesive solution you are considering is actually going to work. Whether an adhesive supplier has suggested the solution or you believe it might be a good option, you still aren’t sure it is the best solution for you.

As adhesive specialists here at Forgeway, we know just how difficult it can be to have confidence in the solution. You feel like you need to test it so you can be sure it is the right option.

We have helped hundreds of companies in multiple industries with this exact issue. Knowing what test(s) you might need to do is difficult.

This article will go through why you need to test, the different testing methods, and what the outcome of the test should look like.

When you finish the article, you will have a greater understanding of adhesive testing and have a good idea of what test methods you may need to carry out. 

Why do you need adhesive testing?

Sometimes it can be unclear why you even need to test in the first place. Sound like you? Don’t worry, it’s a very common stumbling block in the buying process. 

I could go into great detail about how and why you can have ‘peace of mind’ and ‘rest assured’ that the product will work and how the solution is the best. But at the end of the day, that doesn’t really help anyone. There is still a valid reason our customers like to test. It comes down to proof.

How can you prove that the solution is going to work? This is where your journey as a buyer can become very frustrating.  Companies (like yourselves) rarely like to take the risk in changing from what they already know.  On top of that, how can they convince all relevant stakeholders that you are investing in the right solution?

It’s here, at this very point that we often see adhesive and sealant buyers wander off into the mysterious world of “testing”

Adhesive testing can be a challenging process if you don't know what you are doing

There is often a lack of clarity on what you could class as a ‘beneficial test’ and what a ‘successful outcome’ of the test would look like. A lot of companies invest time, resources, and money in finding potential solutions but get lost in this testing phase and never get the benefit of what a real solution could do for them. 

They feel as though the testing process will build trust internally and justify the decision to make the change. It should do this, but it can often not end up this way. 

So we understand how you need to be able to trust the product (by testing) before you go ahead with the change, but you need to get it right.

By the way, I’m not saying you don’t trust the supplier’s word about the quality of the product. Most adhesive suppliers are very reputable and are honest about the products they supply. They will tell you how you can have ‘peace of mind’ about their product, how you can ‘rest assured’ the product will be the solution and won’t fail. But we know it’s not always as easy as that.

You can’t ‘rest-assured’ or have ‘peace of mind’ until you know for sure that the product is going to work. This is why 90% of our customers like to test the product before they go ahead and purchase it.

Testing allows you to see the proof that the suggested product will work in your situation.

90% of our customers like to test the adhesive product before they go ahead and purchase it.

Bruce Ellis

What are the different types of adhesive testing?

Before going into the details about the different types of testing, you should have an idea of who you want to carry out the testing. 

You can test the products yourself. The supplier can test the products for you. You may even need the help of an independent test house.  Or you can have a mixture of all of these. This work doesn’t necessarily come for free, some adhesive suppliers will charge you extra for testing. You may want to make this decision after you understand which testing methods you will need. 
The following list will show you the most common testing methods. The list is in somewhat of a chronological order. The first methods are the ones you should typically consider first.

  1. Adhesion testing – This is the first test method you need to consider. There is little point in doing any other tests if you have issues with the product simply sticking to your substrates. Ribbon bead adhesion testing is a quick way to ensure the adhesive or sealant solution will stick to the substrate. We would also refer to this method as ‘cut and peel’. It is basically where the adhesive is applied to the substrates, left to cure, and is then cut at a 90° angle to the substrate. This test will take as long as it takes the adhesive to cure, which is typically 72 hours.
Cut and peel testing of adhesives
Cut and peel testing
  1. Cataplasma testing – This is similar to the ‘cut and peel’ test process, but still not exactly the same. This test will put the adhesive through a similar climate in which the end-product will likely be exposed. So, let’s say a caravan will be used in Canada. The adhesive on that caravan needs to be able to withstand the extreme cold. The climatic durability test will put the adhesive through similar conditions to that which it could be exposed. And then the cut and peel method will determine whether the adhesive has withstood that test.
  1. Strength & Flexibility Testing  – Determining whether the adhesive/sealant has enough strength and flexibility. You may be wondering why we have put strength and flexibility in the same test. This is because they are often interlinked. If you have an adhesive with high strength but limited flexibility, any significant movement in the structure you are bonding will cause the adhesive to crack. This is why flexibility and strength are tested in conjunction. The safety data sheet you will receive from the adhesive supplier will give you the details on the strength and flexibility, but it’s good practise to test the strength with your substrates on a tensometer.
Technician testing adhesives in laboratory
A tensometer is used to test the strength of an adhesive
  1. QUV Testing – This is to check whether the adhesive/sealant is durable when exposed to UV rays. This test is particularly relevant to sealants. It is mainly for when the end-product is likely to be exposed to high amounts of UV. The UV can cause yellowing and serious degradation over time, therefore breaking the intended seal/bond. The adhesive/sealant is exposed to high radiation levels of UV light in a test machine.
sealant that has yellowed
Sealant can turn yellow when exposed to UV
  1. Prototyping. This is usually the final test that the customer will conduct. It involves testing the adhesive/sealant solution on the end product for a prescribed period of time. The intended outcome is to see whether the adhesive/sealant fails when it is used in the situation it is intended to improve. A typical time period for this test is around four weeks, but it is totally up to you. We would often say that if all other relevant tests are done well, prototyping is not actually necessary. 

For highly demanding and high-risk applications in industries such as aviation and rail, there are many more types of testing that you may need to consider, including:

  • Fire retardence testing/Fire resistance testing. (Yes there is a difference).
  • Impact resistance testing
  • Chemical resistance testing  

Whilst these tests are more specific, you should approach them all with the clarity that we are discussing in this article.

What does a ‘good adhesive test result’ look like?

This is a very subjective part of the testing. ‘A good result’ will depend entirely upon what you want from the solution. Our definition of ‘good’ could look entirely different to your definition. Yes, we can offer guidance, but ultimately you are the one who decides what ‘good’ looks like. Adhesive suppliers will complete certain test standards, like DIN, ISO and ASTM methods. Interpretation of these results isn’t always easy. 

Having said that, any sort of testing should have a clear definition of ‘good’ before the testing begins, especially if there are no numerical ways to deem a pass or fail criteria.

One of the things that our customers usually look out for is ‘cohesive failure‘. This can be a good indication that the suggested solution is able to meet your needs as it shows the adhesive’s bond to the substrate is stronger than the adhesive itself. 

cohesive failure is where the bond to the substrate is stronger than the glue itself.
Cohesive failure with glue on both substrates/surfaces

Cohesive failure isn’t always the best way to define ‘good’ though. It often takes quite extreme force to cause cohesive failure. This extreme force is often not representative of the force the end product is likely to come under.

Therefore, cohesive failure does not always represent what your ‘good result’ should look like. 

Whatever you define your ‘good result’ as, you should define it before you commence the testing process.

What should you do once you have completed the testing process?

As soon as you have concluded your testing process, you’re going to want to analyse the results. This is a stage where some people get stuck. It can be difficult to decipher what the test results even mean.

However, this may not be you. The results might make complete sense to you and you are able to translate their meaning. If this sounds like you, the test results should have given you a good indication if the product is or is not a good fit for you. You will be ready to make your purchasing decision.

If you are struggling though, don’t worry. Whether you have done the testing process yourself or you got the adhesive supplier to do the testing for you, the test results may not be clear to understand. We regularly come across this issue and we always translate the results into an understandable language where possible.

But we know that this may not always be the case. We would suggest you contact the adhesive supplier and get them to translate the test results so that you are able to make the decision about whether the product is a good fit.

The testing stage should not be a stage that holds up the buying process but we know it so often is. We’ve explained why in this article, and you will now have a good idea of what you can do to stop testing from becoming a significant stumbling block. 

Nonetheless, you may still want the help of a professional to guide you through the testing process.

Or you may want to read about some of the different test methods in chapter 7 of our Ebook. You can download it by clicking the banner below.

Download the chapter 7 about test methods