I've noticed on a couple of forums that people are under the impression that 5 minute epoxies are not waterproof, so aren't used for submarine model making or repairs.
I've been selling epoxies for over 25 years and I've only every encountered this on submarine forums, so I'm puzzled how this snippet of information came about. It seems to be 'cast in stone' these days.
The hardener in these epoxies is a mercaptan, and has a strong, garlic-like odor to it and is easily recognizable. It does not have the same adhesive strength as the slower curing materials, and it is usually a paste-like material, so I can imagine it letting loose on a plastic or very smooth surface, so maybe this is the reason some have had failures?
I've used 5 min epoxies in many underwater situations and never had any problems, so I'd like to hear from anyone who has, just to see what they did.
The base part of the resin system is usually the same material used in the slower curing resins, only the hardener being different, so the material is actually waterproof. Bond strengths are lower, but still strong enough for anything on a submarine model.