Hi
I have done a lot of testing in the past 3 weeks using all sorts of material combination to test rigidity, weight, resin usage and so on
The best 2 samples were with EasyCell75 and 3D Core

Easycell is PVC foam, so I guess I can join sheets with Solvent Cement or similar used for PVC pipes.
What can I use to join the 3D PET Core?
I'm infusing and the gabs between sheets are visible
thanks

Epoxy.

Thanks, should have thought about that
my brain is a bit slow today

Yes as said you can epoxy bond it. Or if the mould is a stable shape, just butt join the pieces of 3D core with the hexagons helping to ensure it stays where it is. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant