Epoxy Setting Speeds

Epoxy characteristics vary by formula. Some companies offer more than one hardener speed. Thorough mixing is key. December 2, 2006

There are generally two types of hardeners available in the market for epoxy adhesives, fast and slow setting. Do they give the same bond strength on drying? Can the fast and slow setting hardeners be mixed in definite proportions to give a specific or median drying time, so as to get a setting time of say 2 hours or 4 hours or 6 hours?

Forum Responses
(Adhesives Forum)
From contributor E:
That's going to depend on the type, or ratio of hardener to resin, and the formulator. The specs range all over the place on tensile strength, elasticity, chemical and water resistance, etc. Some require very careful measuring of ratios, some you can be a little sloppy with. Some you can vary ratios to change working properties and even mix slow and fast hardeners, and some you can't. The best thing is to talk to the manufacturer/dealer and tell them what you need the epoxy to do and what you desire for open time and clamping time, and let him tell you what he has that will meet it.

One thing to remember with epoxies is that the hardener and resin don't really like to mix easily. You need to follow the mixing times and procedures laid out by the formulator. Most people way under mix their epoxies and then complain about inconsistent results.

From contributor K:
I agree with all that contributor E said, and would like to add that time and temperature are dependent on the other. The warmer, the faster the cure, or shorter the pot-life. There are a lot more than two hardeners.

From contributor A:
The other guys have it about right. Epoxy resin needs specific resin/hardener ratios to maintain a complete chemical reaction. Most companies supply 2 to 5 or more hardener speeds. The older resin systems (like West System) have an incompatible hardener system. No mixing is allowed. Newer resin systems (like MAS, System Three) have hardeners that are mixable. The usually offer fast, medium, and slow. (The medium is simply a 50/50 ratio of fast and slow). Most people buy fast and slow and mix any ratio they prefer. I also prefer the MAS and System 3 resins because they also have two resins (thick and thin), which you can also mix in any ratio. They are mixed 2:1, so in large quantities it's easier to mix, versus West Systems 5:1 system.