Rocketpoxy should last 1-1/2 years if stored correctly, What this means is to keep it sealed as much as possible ( don’t leave the lids open overnight or for long periods of time), try to keep it stored above 60 Deg. F ( try not to freeze it). Also after such a long time there could be some separation and settling of fillers, So if sitting for a very long time make sure to mix each side independently, that is A side and B side so the epoxy and fillers are fully mixed.
To answer Gregg about his Madcow mini screech failure, there are just so many variables here at work that it may be hard to nail it down. I know it is not the Rocketpoxy if mixed and used correctly. There has been way to much research and way too many high powered rockets using RP over many years ( estimate at least several thousand rockets have been built using Rocketpoxy including many university rocket teams) so Rocketpoxy is probably one of the most used and tested high strength epoxy for building HP rockets.
I have seen some unbelievable crashes where Rocketpoxy has held up where other epoxy would have just completely shattered. I personally had built a 8 inch diameter very heavy all fiberglass Gizmo rocket built like a brick house with Rocketpoxy that I had launched at a previous 2012 Midwest power10 drag race, the rocket came in ballistic from 6,000 feet, it was screamer, lots of high G forces when it hit the ground, I think if you Google this there are still videos floating around showing this, rocket was about 3 to 4 feet into the solid earth ( total core sample) , it was dug out and other than a shattered nose cone the rest of the rocket held together 100%, after replacing the nose cone and electronics, it was launched several more times successfully and I still have it and launch it to this day, in fact thinking about launching it at the next Michiana Rocketry launch at Three Oaks, MI on February 18th. But be realistic if your rocket comes in without a chute or ballistic with high G forces no epoxy manufacturer can guarantee nothing will fail and you shouldn't really expect this either.
But I will take a few guesses at some possible reasons that may have aggravated your situation. Don’t take any of this personally, and yes maybe you did most everything correctly, but I am looking at this forensically from your failure to diagnose this from just what little information I have to go on, and not being personally involved with the build it makes it even more guess work.
General assembly issues:
1) Was the mold release completely cleaned off all the surfaces
2) Did you use a 60 to 80 grit sandpaper to rough up all the bonded surfaces extremely well
3) Your external fillets seem to be extremely small and weak, consider making larger fillets
4) Did you do internal fillets correctly if not this may have helped the fin separation ( I would always recommend doing them on a fiberglass FW rocket), it sounds like you had no internal fillets at all because of the tight space, what I do in extremely tight situations is to mix ( I wait from 15 to 30 minutes after mixed so I have the viscosity I want, thicker for shorter pours or thinner for longer length fin pours), and simply pour the Rocketpoxy from the back open end of the airframe/internal fin area by tilting the rocket airframe/fin assembly nose cone end down so the RP will ooze down inside the joining crack area of the internal fillet, and using a small flashlight I observe where it is and using levels of airframe tilt to get it where I want it to be, then I level out the rocket and fixture in a position where the RP stays in the internal fillet area, and then be patient enough to let it cure before I rotate and do the remaining internal fillets. It really is quite easy and fast when you get the hang of it.
5) Were your fins buttered up with enough epoxy and correctly mounted square against the motor tube, was you motor tube sanded with 60 to 80 grit sandpaper where the fins attach
6) Were you patient when building and made sure RP had cured fully before assembling the next part, for example if you were doing internal fillets and buttering of fins and rotated rocket before it is cured some may have dripped off leaving a thinner weaker bond.
1) Sounds like it was sitting for a long time, you purchased in March 2015, built rocket in latter 2016 you do realize that was almost 1-1/2+ years ago because we probably made it several months earlier from when you received it as it takes time to ship to distributors and them to ship to you. C'mon Rocketpoxy states 1-1/2 years life, this could have been close or even past that limit, If I was building an expensive fiberglass Madcow rocket I would have sprung for a fresh 8 ounce RP kit for $12 just to be sure and not tried to use a 1-1/2 year old material.
2) Was the RP stored above 60 Deg F, it sounds like you had it in a garage maybe some night got very cold in there.
3) Did you thoroughly mix each side of the RP after it was sitting so long, if the fillers settled and/or separated out and wasn't fully mixed this may have caused some issues.
4) Was this the bottom of the RP jar, was the lid left off for extended times on previous builds, how well were the jars lids sealed
5) Of course there could be other issues as well, was it mixed at a 1 to 1 ratio, was it mixed fully, temperature when applied, how cured the epoxy was when applied, etc.
Photo on left is my 8 inch Gizmo that was built completely using Rocketpoxy right after the ballistic crash from about 6,000 feet, photo on right is after I spent an hour digging it out.
The next flight of the Gizmo a few months later after digging it out and replacing only the nose cone and electronics, no airframe or fin structure work had to be re-done thanks to the Rocketpoxy.