The internet is riddled with questions from ladies and gents who have had their epoxy repairs go awry. The time it actually takes for a putty or paste epoxy to set and harden – adequately – seems to be a great mystery, and is never as “cut and dry” as what the label says when you start out on your mission. So what to do?
There are many factors involved that can affect the cure time of epoxy, because there are complicated chemical reactions occurring during the process. Epoxy is not glue. But that’s a good thing – because at the end of the project, you will be getting a super-hero style bond, done properly. In some cases, the bond created through the use of epoxy polymers is much stronger than the original substrate. (Yes, we think that’s cool, and it’s why epoxy is always worth the effort!)
Things to remember about the hardening or “curing” rate of varying epoxies
- The time quoted on packaging is not necessary the actual cure time. This is the “working time” or “pot life” of the product after mixing, and it’s the point where the epoxy can no longer be deformed without structural damage. The working time will give you an idea of how much to mix for your application, and how fast you need to hustle to make a go of it.
- A slight temperature change can have exponential impact on cure time. Remember that the temperature of the materials being joined is even more important than the epoxy’s temperature! If you are in a warm room, but your surfaces to be bonded are bitter cold, there will be problems.
- Any surface contaminants on your project surface that are oil or solvent based will also affect the bond, or potentially cause it to never set at all.
- Cured epoxy, such as our PC 7 paste epoxy, will often produce a better bond strength at moderate heat cure, as compared to room-temperature cure. This is because of the better “wetting” of the substrate because both the surface energy and viscosity of the mixed epoxy is lower.
Protective Coating Company’s extra tips to give you the best epoxy repair results
- Always mix the appropriate ratios (usually a 50-50 mix). Changing the ratios even slightly can have very negative effects, or may cause your project not to harden at all. Don’t think that adding extra hardener will give you a stronger bond – this is not the case at all.
- If you need to clamp your project, don’t do it too tightly! You will squeeze out all the glue and the scales may pop off later. Clamp just snug enough to hold it in place (about the same as finger tight).
- You can warm your epoxy (gently) prior to use. Some folks have had success with a hot water bath to loosen up the epoxy and hardener before. It mixes beautifully, spreads very easily AND there are few if any bubbles.
- If you do end up with bubbles in your epoxy, use a hairdryer, with caution, until the bubbles dissipate.
- If working with small projects and you are in need of exact measurements, try using one ounce dosage cups to be sure of the ratios. The cups are disposable, cheap and readily available at your local hobby shop or drugstore.
Now you’re ready to a DIY epoxy weekend warrior!