1. Not using the correct mix ratio. For instance: if the mix instructions call for a 2:1 mix (that is, 2 parts of "A" with 1 part of "B"), DO NOT vary from this ratio! Some people are under the misconception that "if a little "B" is good, a little more is better". Not at all! Epoxies are formulated for a specific mix ratio, and that mix ratio needs to be maintained to ensure that the proper chemical reaction occurs between the two parts. Adding more "B" (a common mistake) may seem to make the cure progress faster, but at the expense of ultimate cured properties. Don't do it.
2. Not mixing the two parts thoroughly. Many people begin their fabricating careers with the unsaturated polyesters, then advance to the stronger and more versatile epoxies as they learn more about the relative performance capabilities of the two different chemistries. But, while it is somewhat OK to mix the polyester and cream hardener "with a lick and a promise" (the cure will still progress adequately, albeit slower), this cavalier attitude towards mixing will definitely NOT work with the epoxies: the "A" and "B" MUST be thoroughly mixed, again to ensure that the appropriate chemicals are in intimate contact to carry out the necessary cure reaction. Thorough mixing for 30-60 seconds, occasionally scraping the sides if the container, is usually sufficient. (Be careful, however, not to stir so vigorously that you whip sir bubbles into the adhesive).
3. Not following application instructions regarding limitations of the product, such as surface preparation, temperature issues, moisture concerns, etc. The data sheet lists specifics that must be complied with if proper performance of the adhesive is to be expected. A common issue is temperature: for instance, if the data sheet says to not use below 50 degrees F, then don't use the adhesive if the temperature is 35 degrees! The adhesive simply will not cure.
Pay attention to these 3 ways to abuse an epoxy and you’ll eliminate a lot of headaches!
