If you are using a tubed adhesive reccomended for the pvc panels, you will still need to let the render dry completely. this might take a bit of time. Get a bit of heat into the room, and ventilate it well to shift the moisture. Looks like you have some old skim on the walls, it might pay to seal the walls after the drying period. Use sbr, several coats. Drying could take anytime, but don't rush, that will lead to a cock up.
Hope this helps. There will be more advice from others later I'm sure.