November 17, 2021 by Brent Phillips
A combination of epoxy resin and a hardener incites an epoxy chemical reaction as it cures forming an epoxy coating. When it is fully cured, the resulting product is a durable coating with numerous desirable features. The base of the epoxy resin mixture, without any additives, which controls the epoxy mixture’s overall cure time is the cure speed of the hardener and maintenance of epoxy resin temperature.
Every hardener has a specific temperature range that encourages the epoxy to cure, just at different rates. The temperature and conditions of the worksite are vital factors in selecting the right hardener with enough time for application.
The temperature of curing epoxy controls how fast it cures as heat speeds up the chemical reaction of epoxy components. The temperature is a combination of two factors: the ambient temperature, like air and surface material temperature, and exothermic heat.
Exothermic heat is generated heat from the chemical reaction that cures epoxy. Depending on the amount of mixed epoxy in an area, the amount of heat produced from the chemical reaction changes. In a thicker mass, more heat is retained which causes a faster reaction while a thinner layer slows the curing process as it is less affected by exothermic heat.
While there are ways to increase the cure time to allow more time for application, there still is a countdown to cross the finish line before time is up. The countdown begins after mixing the resin and hardener to incite an epoxy chemical reaction.
The starting point of the cure time countdown is when the mixture is in an applicable liquid form. This is also the point in time for assembly and clamping to assure a dependable bond. To have more time available for coating, lay-up, or assembly, it is best to apply the mixture quickly.
As the epoxy is assembled and applied, it will start to solidify due to the generated heat from its chemical reactions. This initial cure phase when it begins to gel will change from a gummy consistency to the hardness of rubber. While the epoxy is no longer workable as a whole, it is still only partially cured. This means that a new application of epoxy will still chemically link with it, without forming any seams in its surface without special preparation.
Once the chemical reaction is complete, it can be dry sanded, shaped, and have the clamps removed. At this point, the product has reached about 90% of its ultimate strength and durability. It will still continue to harden at room temperature over the course of several days. If a secondary layer is needed, the new application of epoxy will not chemically link to the cured layer of epoxy. To achieve a secure secondary bond, the surface must be properly prepared and sanded before recoating.
There are lots of factors to keep in mind concerning creating an epoxy surface such as the resin/hardener combination, controlling the cure time, breathing the fumes from the chemical reactions, or even how to determine when the curing process is finished. If you are interested in epoxy surfaces but are unsure, just leave it to the professionals at Cunningham to get the job done right – hassle free. Here at Cunningham, our professional teams have a complete understanding of epoxy chemistry to recommend and plan the necessary steps to take to complete your project.