Hi guys...I'm messing around with hand layup of twill carbon in a complex three part mould. The three parts are laid up seperately and then joined with an inflation bladder. There is an advantage for me in letting the parts cure to B stage (not sure wha range of cure that covers) and then joining with fresh uncured epoxy. The question is what state can you let epoxy cure to before it needs sanding for good adhesion and what is the chemical process that stops expoxing adhereing well once cured?
Cheers...Chris

Once you go past the B stage and it begins to loose tack, you start to see a reduction in cross linking as the epoxy is getting closer to being cured. Realistically there will be some cross linking in a room cured epoxy even for  day or two after reaching demould hardness. However it won't be much hence the need to key the surface to aid with the mechanical adhesion to the resin.  You also find with a smooth surface, wet laying the next layer on without keying can lead it to fisheying off causing even more problems long before you get to potential delamination issues.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thanks Warren...so I'm assuming B stage is the classic tacky but not coming off on your finger that's displayed in some of your videos.