1K Vs 2K adhesives; what is the difference, and which is best for you?

When you are analysing your adhesive options, you will likely come across the debate between 1K and 2K adhesives. 

Here at Forgeway, we are adhesive specialists. We manufacture over 3000 tonnes of 1K and 2K adhesives annually so we know the difference between the two. We’ve helped guide 100s of companies to find the best choice for their application and process. 

However, neither is absolutely better than the other. Whilst we can advise you on the best option, your choice should come down to which option works best for your application and process.

We wrote this article to inform you about the differences between 1K and 2K adhesives so you can form your own opinion about which is better. By the end of this article, you will understand the key characteristics of both. 

That will allow you to become an informed buyer and know which adhesive option will solve your bonding problems.

What is the difference between 1K and 2K adhesives?

First of all, we should establish what 1K and 2K adhesives actually are. These are adhesives that fall into one of two categories: structural adhesives and sealants. The ‘K’ stands for component, and the number (1 or 2) stands for the number of components there are. 

1K means there is one component. That means it will arrive ready to use as a single unit and will require an external factor (like moisture or heat) to initiate the curing process. 

MS polymer adhesive
One-part MS polymer adhesive

2K means there are two components. The two parts are often called ‘part A’ and ‘part B’ or ‘resin’ and ‘hardener’. They will mix together as you apply them triggering a chemical reaction which then starts the curing process.

Polyurethane adhesive
Two-part adhesive (1:1)

2K adhesives come in different ratios. Typically the ratio is 1:1 between parts A and B, but you can also get 2:1, 4:1, and 10:1. The reason these different ratios are available is simple; versatility. The formulation you want determines what mix ratio you have.

What are the advantages of 1K adhesives?

Now you have an idea of what a 1K adhesive is, you will want to know why you might want to consider choosing them.

1K adhesives are the ‘safer’ option

When there is just one part, there is a lot less that can go wrong. Any problems you have will typically be down to an issue with the product or improper application. A typical example of this is where you leave the adhesive too long and it has already started to cure. You don’t have to worry about ensuring the adhesive mixes correctly; the manufacturer takes care of that.

It is easier to apply 1K adhesives

This is similar to the previous point. Because there is so much less to go wrong, it is easier to train the person applying the adhesive. There is less to worry about when learning how to dispense 1K adhesives and they will not need to constantly quality check the adhesive after it has been applied.

Applying sealant to a bus

1K adhesives cost less

Whilst it is difficult to put numbers on the difference in cost, we can confidently say 1K adhesives will typically cost you less. You don’t need speciality equipment to ensure the adhesive mixes correctly. This keeps your cost down. You can also use foil packaging instead of plastic, which keeps the cost down due to it being cheaper. This will also cause less wastage.

What are the disadvantages of 1K adhesives?

Before you go racing ahead with using 1K adhesives, there are a few things you should be aware of first.

1K adhesives require the right conditions to cure

As we have already described, 1K adhesives require the external environment to cure. This can be a problem if you don’t have the right environmental conditions. Sufficient moisture and having the right temperature are the two main conditions you need to get right to ensure the cure will be effective. A prime example of this is MS polymer adhesives. They are one-component and require moisture to cure. If the climate in which they are curing is dry and lacks humidity, the cure will either take a lot longer or will be ineffective.

MS polymer adhesives require moisture to cure
1K adhesives will need external factors to start curing

You don’t have much versatility with 1K adhesives

1K adhesives will give you fewer options when it comes to tweaking characteristics (like strength or speed of cure). The reason for this is that you only have one part that can be adjusted. So if you want to adjust the cure speed or hardness, it is more difficult to do this with a 1K adhesive.

What are the advantages of 2K adhesives?

So you know the advantages and disadvantages of 1K adhesives, but what about 2K adhesives?

2K adhesives also have some advantages which might make them a suitable option for you.

You can adjust the adhesive’s characteristics

We already mentioned this as a disadvantage of 1K adhesives, but it is something you can do with 2K adhesives. The ability to adjust the formulation can allow you to tweak the adhesive to meet your characteristics. As an example, you can set the adhesive to have a very specific open time before getting it to cure very quickly.

You can adjust 2K adhesives formulation
Purok VX61-40 & Purok VX61-15 have different cure times

2Ks are traditionally stronger

You can get adjustments made to some high-strength adhesives which means you can get them as one-component. However, you will find that the stronger adhesives will be two-component.

You have more control of the cure of 2Ks

The versatility of 2Ks will give you the ability to increase/decrease the speed of the cure of 2K adhesives. However, you also don’t have to worry that the adhesive hasn’t ‘through-cured’. This is because 2K adhesives aren’t reliant on external conditions (like temperature and moisture) to start the curing process. The hardener part of 2K adhesives will start the curing process and will ensure it cures the whole way through the adhesive.

What are the disadvantages of 2K adhesives?

Like with 1K adhesives, there are several things that might suggest they aren’t a good fit for you.

2K adhesives cost are the riskier option

This is the main disadvantage to using 2K adhesives as it is very difficult to guarantee you will be able to get the application process right every time. The two components sometimes do not mix correctly as you apply them. When this happens, the adhesive will not form a sufficient bond, resulting in adhesive failure. None of the benefits we mentioned above will apply if the two components don’t mix effectively.

You need to train the operators on how to use 2Ks

As we were saying in the point above, there is a risk that the adhesives will not mix properly when you apply them. But in order to reduce that risk, you need to train the operators. There are processes the operative will need to follow so they can be sure the two components will mix.

‘Balancing’ the cartridge (getting parts A and B to come out at the same time) takes a degree of skill and is one thing you may need to train them on. It can be difficult to master but is essential if you want the adhesive to mix effectively.

2K adhesives mixing
2K adhesives require skill to mix them correctly

2K adhesives will cost you more

We mentioned the cost already, but we should perhaps explain why 2Ks will cost you more. The specialist equipment you will need to apply the 2K adhesive will cost more. The packaging that the 2K adhesive requires also costs more. And if you need to train your operatives, that is going to be an additional cost too.

1K or 2K adhesives; Which is best for you?

So neither 1K nor 2K adhesives are the perfect options, they both have drawbacks. How are you going to decide which one you should go with?

Here at Forgeway, we are specialists in all things adhesives. We would always advise you to go with a 1K adhesive. There is so much more that can go wrong with 2K adhesives. So we recommend you make sure 1K adhesives aren’t going to be a good fit before looking to use 2K adhesives.

But ultimately the decision lies with you. You need to decide what you want from an adhesive before choosing to go with 1K or 2K.

If you are still unsure about whether to choose between 1K or 2K adhesives, you can reach out to a member of our team who will be able to advise about your specific situation.

Or if you want to learn more about 2K adhesives, you can read our articles on epoxies and MMAs. These two articles will give you a better understanding of the two main 2K adhesives. 

However, if you want to find out why we would always advise going with a 1K adhesive, you can learn more by reading our blog on MS polymers. They are the main 1K adhesive and the article will show you why they are such a good adhesive option.

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