What To Know About Structural Adhesives And Time

Let's Talk Terminology

Despite the fact that adhesives are in most of the products we own, the average person rarely has to think about it beyond the craft glue they occasionally use. Phrases like open time or set time hold no meaning and have likely never crossed our minds. But for those who work with adhesives daily, knowing the difference matters.

So whether you're the authority on adhesives or new to glue, having a good understanding of product terminology can help prevent project hiccups and delays. That's where the experts at Gluegun.com come in. Read on for our comprehensive guide to the most common terms to know if you're wondering how much time you have to bond your parts and when they will be at full strength.

What Is An Adhesive's Open Time?

Because timing is so crucial in the world of adhesives, you'll frequently see the words open time used in product descriptions, technical data sheets (TDS), and more. Open time describes the maximum time that can pass between applying an adhesive to a surface and when it begins to cure. During this time, the substrates you use can be adjusted or repositioned before the adhesive starts to set or cure. 

When choosing your structural adhesive, you'll need to ensure that the open time corresponds to or is longer than the project's application time. If the adhesive's open time is only 30 seconds long, but it takes you that long to apply it to your substrate and another 30 seconds to form the bond, this can result in poor wetting of the second substrate. And subsequently, a weakened — if not failed — bond overall.  

In some cases, you'll see working time in place of open time. Used interchangeably, working time is another way of indicating the amount of time an adhesive remains workable once applied. 

Set time vs. Fixture Time

While set time and fixture time are another set of words that get lumped together, they have their own distinct meanings. Set time, as the term alludes to, refers to the time it takes for an adhesive to "set" or become stiff enough that it can no longer be manipulated or adjusted. It is also a measure of the adhesive's consistency and determines the point at which it becomes unworkable.

Fixture time, on the other hand, is the amount of time it takes for the adhesive to not only bond but also reach handling strength. Handling strength is the point at which full bond strength may not be in place, but the bond is strong enough to move the part freely with little risk of separation. All this to say that once the adhesive's recommended fixture time has lapsed, you can carefully move your substrates without disturbing the bond. 

How Is Cure Time Different?

Although it may seem like cure time is just another way to say set time, cure time is more than just the process of adhesive hardening. Depending on the adhesive and the conditions under which it is used, curing may still take place long after the adhesive stiffens. Think a few hours to possibly several days. During cure time, chemical reactions within the adhesive occur to make the adhesive stronger, harder, and more resistant to external factors.

An easy way to remember it all is to think of these terms like so: 

  • Open time - measures an adhesive's workable time before it sets.
  • Set time - measures an adhesive's inability to be adjusted.
  • Fixture time - measures an adhesive's time to reach handling strength.
  • Cure time - measures an adhesive’s time to reach full properties.

Please note that these terms may vary depending on the context or the specific adhesive used in your application. We recommend consulting the manufacturer's technical data sheet for more info on a product's properties and behavior. 

Factors Besides Time That Affects Bonding And Performance

Besides time, other factors can also affect bonding and performance. Here are some important ones to note: 

  1. Temperature: Higher temperatures generally accelerate the different times, while lower temperatures can slow them down.
  2. Humidity: Moisture-cure adhesives typically cure or set faster in high-humidity environments and slower in low-humidity environments.
  3. Mixing Ratio: Many adhesives require a specific mixing ratio to achieve the correct cure or set time. If the ratio is incorrect, the adhesive may not cure or set properly or may take longer to cure.
  4. Catalyst or Accelerator: Some adhesives require a catalyst or accelerator to initiate the curing process. If the correct amount is not used, the adhesive may not cure properly or take longer.
  5. Adhesive Type: Different types of adhesives have different properties and behaviors, some cure or set faster than others. 
  6. Application Thickness: The thickness of the application layer can also affect how long it takes for certain adhesives to stiffen up or cure. Thicker layers generally take longer than thinner layers.
  7. Surface Condition: The surface condition of the materials being bonded can also affect bond performance. For example, a rough or porous surface can yield better bond performance in some cases.

If possible, remember to account for all of these factors when considering and selecting an adhesive for your project. 

Additional Questions?

Now that we've given you a general overview of some of the terminology you'll see around structural adhesives, we hope you'll feel more confident navigating product descriptions and instructions. 

Should you still have questions after reading our guide, don't hesitate to contact one of our adhesives specialists. We're always happy to help clear up any confusion or advise you on a specific adhesive and application method. 

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