Im trying to bond 2 relatively simple flatish carbon components together as part of an assembly. They have been infused with vinylester resin however when I try using vinylester resin to bond them firmly together they come apart with little force.
Would epoxy be a better to stick them? or perhaps I need to bond them together with vinylester while they are still a bit sticky?
did you try using a rough-grit sandpaper to scuff the surfaces?
I wonder if acetone or something similar would disolve the surface enough for you to pour on some resin and actually create a chemical bond.
the surfaces being bonded were straight off peel ply rough texture but I let the parts harden before bonding. The thing is I cant bond them together in the mould and if I attempt to take them out while still a bit green or soft then they would likely crease and mess up!
are you just using resin to bond??
Try using some cabosil or other type of filler to make the resin thicker so that it stays in contact with both surfaces.
I use epoxy and a layer or 2 of F/G (basically a wet layup on the bond line) to bond the parts I do like that.
It’s a well known fact in boatbuilding and repair businesses that vinyl or polyester resins don’t bond well to each other once cured. At best you’ll get a weak mechanical bond which as you’ve seen comes apart pretty easy. Epoxy is the best choice and in most instances the only choice for working with fully cured resins.
There are other polyurethane adhesives that work nearly as well but I have no experience with them. 3M makes a polyurethane adhesive called 5200 which will stick pretty much anything to anything else. If it’s not a cosmetic part it might work. Curing times are much longer for polyurethane adhesives than epoxies.
Cyanoacrylate’s are another option you could try.
The only time I’ve ever had to do such a repair I used Interlux 2-part epoxy filler and it works great.
yep was just using resin, no filler. I will give it a try. I have wet out some carbon fabric and done it like that before on bigger parts between the infusions but that was with epoxy.
Guess epoxy is the way if the ester parts are unavoidably fully cured. 
Resin is not for bonding.
You need a proper epoxy adhesive to join the parts.