It is a well known fact that the more surface area there is on an object, the stronger the bond will be if another object is adhered to it. I decided to apply this to the puzzle; sanding each face quite roughly so as to provide more area for the paint to ‘hold onto’.
Two thin coats were applied and I left the paint to dry for just over two days. I checked the paint periodically throughout this time and found that the paint was staying on the plastic by the end of the first day, but it still felt a little soft. It wasn’t until a whole week after spraying that the paint had dried properly.
I think sanding the faces and applying the paint in thin layers helped considerably, as the paint has dried and adhered well to all surfaces. However to further strengthen the paint, I will allow a few days drying time after each layer on any future projects.
Before assembling the puzzle, I tidied up the inner facing parts of the piece that had a little paint on them (in hindsight I should have covered those parts with masking tape before the spray painting process).
I think the puzzle looks really nice with the stone effect finish; natural to an extent and aesthetically pleasing in my opinion. It also works very well as a decorative piece both indoors and outdoors.