Nitro,
The type and speed of the epoxy has something to do with old joints that are "peeling" away. The longer cure time epoxy usually penetrates a lot better than the 5minute and 15minute. Five minute almost doesn't penetrate at all compared to the others, and 15 doesn't do half as good as 30. And that'll make or break the joint over time. It's good enough reason by itself to not use 5minute for any construction, and to not use 15minute if you've got 30minute available.

"make or break the joint"..... hmmmm is that a pun?