So far I have been able to get PLA, ABS, and PETG all to stick to an unheated build plate by using plasti dip coating (I use the dip in a can vs the spray and just use $.30 paint brushes to apply). I was struggling to get prints to stick on this makerbot replicator+ unheated bed (and no good way to make a heated bed for it). After just about giving up, i threw some plasti dip on my kapton tape and BAM, perfectly stuck prints. Even the ABS stuck without rolling. When the print finished, it was easy enough to pop off the bed, then just light pressure on the plasti dip (rolling my fingers across the base) it came right off the print! I hope this helps someone and keeps them from smashing their head off of the closest wall while searching for something that will make it stick. Cheers!