It didn't come with any hardener? Well no, it won't harden. It might eventually go dry and crusty, but that depends on the resin, and it would be super brittle in that state anyway.
I had an experience once where I tried to make a shell out of fiberglass resin, correctly mixed with the hardener, but it still didn't set properly. Instead, I just got a bunch of goopy resin that I had to wad up and throw away. I don't know if the MEKP catalyst degraded over time, or if I just didn't mix things correctly, but that's the point when I gave up on fiberglass resin and used Sintra instead.
I doubt that you're going to be able to get the resin to harden up after the fact, even if you somehow mix the catalyst onto the goopy resin currently on the pepakura bio. From my limited understanding of polymerization (like from that Wikipedia link), it seems unlikely that trying to apply catalyst after the fact would result in all of the resin getting cross-linked and forming a solid structure. I think you'll have to reprint your pepakura model and do the paper folding again.
Oh, in that case, you should be OK. Yeah, get the catalyst that's recommended for the resin you're using, and everything should be fine.thanks elkman bro but i havent applied the resin yet thank god i dident even open it its just wen i read the back i found out u need to mix it with hardener then it all came back into mind
i resined my foam armour today, too be fair the first half i added too much hardner
it went hard in about 2 min....oooops
any way next time i added half the amount and it was spot-on
well i used it to harden the armour i made using vinmac's tutorials
the armour i had made i had already painted and coated in PVA glua
i will do another coat of resin tomorrow to the inside of the armour but it looks ok so far, i was worried that the resin would chew into & melt the foam
i dont know whether to use fibreglass resin matting on the inside on the armour to strengthen it more, as it seems ok so far and another god coat on the inside should make it pretty strong.....