So now we have touched on what epoxies & polyesters are and their differences, you are all set and ready for gluing. So, you slap a little of the Part A into a cup, put in some of the Part B, stir, and you're off, right?
Is that all there is to it? Are you confident you've achieved the best that the adhesive is capable of delivering? You may be surprised...let's touch upon: mix ratio, and mixing thoroughness.
If you remember in our previous posts, we mentioned one main important difference in epoxies and polyesters is the mix ratio. In a typical polyester system usage is extremely simple: squirt some of the catalyst into the polyester, give it a "lick-and-a-promise" stir, and you're off! Mix ratios are not critical—use a little catalyst, it cures slowly; use a lot, it cures faster. And the catalyst does not need to be thoroughly mixed in with the polyester; a sloppy stir, and it will still cure just fine.
Epoxies are completely different, however. As is usual when working with a superior product, a little more care is required to achieve the ultimate designed properties. Here, the Part A and Part B MUST be combined in the exact mix ratio specified. Any deviation will adversely affect the ultimate cured properties. Don't be fooled into adding more Part B than recommended to try to speed the cure: it will indeed cure somewhat faster, but the result will be an inferior cure and poor adhesion and strength. And be sure to mix the Part A and B very thoroughly together—the only way to assure complete and proper cure is to be sure the two parts are mixed homogenously. A sloppy stir will result in sloppy cure, producing soft spots as well as "over-cured" and extremely brittle spots.
So pay attention to proper mix ratios and thorough mixing, and you will be rewarded with knowing your epoxy is performing as scientifically engineered to give you a tenacious adhesive bond and long term strength and durability.
